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Microsomia hemifacial. Revision de la literatura.

INTRODUCCION

La microsomia hemifacial (MHF) corresponde a un espectro de malformaciones congenitas craneofaciales caracterizadas por la hipoplasia de los tejidos derivados embriologicamente del primer y el segundo arcos branquiales. Su manifestacion es altamente variable, presentando defectos incluso a nivel cardiaco, vertebral y del sistema nervioso central.

Es la segunda malformacion craneofacial mas comun despues de la fisura de labio y paladar, con una incidencia estimada de 1/5.600 nacidos vivos. (1) Se presenta unilateral en un 70% de los casos, y cuando aparece en forma bilateral, se presenta en forma asimetrica, afectando mas a un lado que otro. (2)

Al ser una alteracion compleja y heterogenea, los pacientes con alteraciones pertenecientes a este espectro han recibido distintos diagnosticos, como Sindrome de Goldenhar, espectro oculo-auriculo-vertebral, sindrome del primer y el segundo arcos branquiales, microsomia craneofacial, entre otros. Aun no se ha establecido un criterio diagnostico comun para dicha entidad. (3)

Su patogenesis obedece a un caracter heterogeneo explicado por diferentes teorias. (4) Una de ellas es la propuesta por Poswillo, para quien la causa seria una disrupcion vascular que produce una hemorragia durante la formacion embriologica de la arteria estapedial, lo que se asocia con alteraciones en el desarrollo del primer y el segundo arcos branquiales. El tamano del hematoma y la lesion del tejido resultante explicarian la morfologia y las diferentes variaciones de MHF en los modelos experimentales, ya que, a mayor tamano, mayores alteraciones en el desarrollo de estos arcos branquiales. (5) Otra de las teorias es la postulada por Johnston, (6) para quien el factor causal seria una alteracion en la migracion de las celulas de la cresta neural hacia la formacion del ganglio trigeminal. Esta falta en la migracion, y por ende la ausencia de interaccion entre las celulas de la cresta neural y el mesenquima celular, tambien se ha asociado a otros problemas observados en pacientes con MHF, como la microdoncia y la hipodoncia, (7) la fisura palatina y problemas cardiacos. (8)

Otros autores sugieren esta relacion entre falta de migracion de las celulas de la cresta neural y MHF debido a que en ausencia de estas celulas existe menor factor de crecimiento vascular endotelial (VEGF, por sus iniciales en ingles). Este factor de crecimiento promueve la proliferacion del cartilago de Meckel y, en ausencia de VEGF, existe una correlacion con hipoplasia mandibular. (9)

Si bien aun no hay claridad sobre su etiologia, se han reconocido distintos factores ambientales y geneticos. Dentro de las causas ambientales, se han observado diversos factores de riesgo asociados a su presencia durante el embarazo, como el consumo de medicamentos vasoactivos, (10) sangrado vaginal durante el segundo trimestre, gestaciones multiples, (11) el uso materno de tecnologia reproductiva asistida (12) y diabetes preexistente o gestacional. (13, 14)

M. Werler ha publicado distintos estudios sobre la relacion entre MHF y el consumo de drogas vasoactivas por la madre durante el embarazo. Uno de ellos es un estudio retrospectivo de casos y controles, en el que se analizaron diversos factores a los que estaba expuesta la madre durante el embarazo, entre ellos drogas vasoactivas como la pseudoefedrina, la fenilpropanolamina, le aspirina y el ibuprofeno. Se encontro que el uso de medicacion vasoactiva en el primer trimestre, particularmente en combinacion con el consumo de cigarrillos, se asociaba con un aumento del riesgo de MHF; tambien se asociaron otros eventos como gestaciones multiples, diabetes, sangrado durante el segundo trimestre y fuerte consumo de alcohol. (15)

Dentro de las causas geneticas, si bien la mayoria de los casos son esporadicos, en algunos casos se ha observado un componente genetico autosomico dominante (asociado al cromosoma 14), (16, 17) un componente autosomico recesivo (18) y alteraciones cromosomicas, principalmente en los cromosomas 5 (delecion de 5p), 18 (trisomia) y 22 (delecion de 22q11.2), entre otros. (19, 20)

Clasificaciones

Las clasificaciones utilizadas en pacientes con MHF han evolucionado con el tiempo, abarcando cada vez mas los aspectos propios de la patologia.

1. Sistema de clasificacion de Pruzansky (1969)

La primera clasificacion utilizada en pacientes con MHF fue realizada por Samuel Pruzansky en 1969, (21) a partir de radiografias de mandibulas de pacientes con dicha condicion. En su clasificacion, Pruzansky observo tres tipos de hipoplasias mandibulares, desde una mandibula relativamente completa (Grado I) hasta una muy pequena y cuya deformidad empeoraba con el tiempo (Grado III) (tabla 1-A). Esta clasificacion cumple solo con la descripcion de la mandibula, por tanto, al ser utilizada en pacientes con MHF, quedan fuera muchos aspectos propios de la patologia.

2. Clasificacion de Pruzansky modificada por Kaban et al (1988)

En 1988, Kaban et al (22) modificaron la clasificacion de Pruzansky, anadiendo la descripcion de las deformaciones vistas en telerradiografias de la articulacion temporomandibular. La gran diferencia se observa en el Grado II, el cual presenta dos subclasificaciones dependiendo de la posicion de la cavidad glenoidea, la cual puede estar normal (IIA) o alterada (IIB) (tabla 1-B).

3. OMENS (1991)

Dada la gran variabilidad en la expresion fenotipica de esta malformacion, en 1991 se postulo la clasificacion OMENS, (23) hecha con base en tres criterios, pensando en que una clasificacion para MHF debia ser inclusiva y versatil, que los componentes anatomicos se analizaran por separado y que los datos se expresaran en escala numerica para que fuesen utiles clinicamente. La sigla OMENS corresponde a un acronimo de las siglas en ingles para las cinco principales manifestaciones de la MHF: O: Asimetria de la orbita (Orbit); M: hipoplasia mandibular (Mandible); E: Deformidad en el oido externo (Ear); N: Compromiso de los nervios (Nerve); S: Deficiencia en tejido blando (Soft Tissue) (tabla 1-C).

3.1 Modificaciones a la OMENS

* OMENS+ (1995): Postulada con el fin de ampliar la expresion fenotipica de los pacientes con MHF hacia las alteraciones extracraneales. (24)

* Representacion pictografica de la OMENS+: En 2007 se introdujo una representacion pictografica (de la OMENS+, (25) la cual fue luego modificada en 2011, (26)) con el fin de facilitar su comprension en la practica clinica, en la docencia y en la estandarizacion de la clasificacion de pacientes con MHF.

4. CFDS (Craniofacial Deformity Scoring) (27) (2001)

Corresponde a la suma de MDS-Mandibular Deformity Scoring (valoracion de la deformidad mandibular) + CDS-Cranial Deformity Scoring (Valoracion de la deformidad craneal). A traves del uso de tomografia computarizada, se analizan diferentes estructuras oseas y se les asignan valores de acuerdo con el grado en que estan comprometidas; los maximos valores son 16 puntos para MDS y 19 para CDS.

Caracteristicas clinicas

Al ser esta una anomalia del primer y el segundo arcos branquiales, la mayoria de las alteraciones estan asociadas a estructuras desarrolladas a partir de dichos arcos, (28) presentando una gran variacion fenotipica. Se puede observar compromiso de:

* Mandibula y ATM: Desarrollo asimetrico mandibular por hipoplasia, ausencia de estructuras mandibulares (condilo y rama), ausencia o anquilosis de la articulacion temporomandibular (ATM). Estudios publicados recientemente mostraron que los pacientes con MHF presentaron retrusion tanto de la mandibula como del maxilar, en comparacion con el grupo control, junto con un aumento del componente vertical; estos patrones fueron mas marcados en el lado afectado y aumentaron de acuerdo a la severidad. (29) La altura mandibular siempre fue menor a lo largo del crecimiento, pero el patron de crecimiento fue similar en ambos grupos. (30) En cuanto a la ATM, se ha visto que el grado de displasia de la mandibula no se corresponde con el grado de displasia del disco, los cuales varian entre cada individuo; mientras que el lado no afectado no presenta mayores alteraciones. (31)

* Orbita: distopia orbitaria (mala posicion), dermoides epibulbares, anoftalmia/microftalmia, blefaroptosis, coloboma retinal o coroidal, entre otras anomalias menos frecuentes. (32)

* Oidos: microtia, anotia, perdida de la audicion, hipoacusia, alteraciones del oido medio.

* Nervios craneales: compromiso del nervio facial y, en casos mas severos, de los nervios trigemino e hipogloso.

* Dental: agenesias, (7) hipoplasias dentales, (33) microdoncia y maloclusiones. Retraso en el desarrollo dental en pacientes con MHF tipo IIB y III, (34) siendo principalmente afectados los dientes mas posteriores. (35)

* Maxilofacial: fisura labio-palatina, (36) macrostomia, hipoplasia de los tercios faciales, inclinacion del plano oclusal (muy variable en angulacion), hipoplasia de los musculos masticatorios, (37) insuficiencia velofaringea. (38)

* Alteraciones extracraneales: principalmente a nivel renal, pulmonar, cardiaco, gastrointestinal, esqueletal y del sistema nervioso central (SNC). (24)

Debido a esto, en el diagnostico es necesario establecer el grado de compromiso de las estructuras involucradas, tanto anatomica como funcionalmente, para asi realizar las derivaciones en forma oportuna a los especialistas en cada una de las areas comprometidas. (Figura 1).

Se observan distintos pacientes con grados variables de MHF. En la imagen A, la paciente presenta una alteracion mandibular izquierda Grado I, con leve desviacion del tercio inferior. La imagen B corresponde a una alteracion Grado IIA, presentando alteracion de la simetria, tanto a nivel del tercio inferior como de las orbitas. En la imagen C se aprecia una alteracion del tercio inferior, con compromiso completo del pabellon auricular derecho, correspondiente a una paciente con anomalia tipo IIB. La imagen D corresponde a un paciente con alteracion tipo III del lado izquierdo.

Otros aspectos estudiados en pacientes con MHF hacen referencia a una mayor frecuencia en la internalizacion de problemas, competencias sociales pobres y menor aceptacion por los pares--lo cual se observo mas en las mujeres con madres jovenes al momento de nacer y con otras alteraciones ademas de la mandibula. (39) Tambien se ha visto una mayor frecuencia de ronquidos y otros sintomas de trastornos respiratorios del sueno. (40)

Si bien el diagnostico es principalmente clinico, diversos examenes complementarios permiten un mejor analisis de la patologia. La ortopantomografia (Figura 2) permite un analisis inicial de las estructuras mandibulares y maxilofaciales, evaluando ambos lados en una misma imagen. Una telerradiografia de perfil permite evaluar, a traves de la cefalometria, las relaciones entre maxilar y mandibula, mientras que una telerradiografia frontal permite observar el grado de asimetria y desviacion mandibular. Una radiografia oclusal otorga una vision apropiada de la boveda palatina en caso de fisura labio-palatina.

En las imagenes se observan ortopantomografias de pacientes con MHF, todas del lado derecho, pero con distintos grados de severidad (imagen A: Grado I; imagen B: Grado II e imagen C: Grado III). Se puede observar como, a medida que aumenta la severidad, la simetria entre las ramas y otras estructuras mandibulares se va reduciendo, y se pierde completamente la forma condilar en la imagen C.

Una forma alternativa de evaluar la MHF es a traves de la tomografia computarizada en 3D (TC3D). Si bien permite una vision mas realista y detallada, esta tecnica requiere aplicar una gran cantidad de radiacion sobre el paciente. Un estudio de Takahashi y colaboradores en 2013 sugiere el uso cuidadoso de ambos metodos (radiografia panoramica y TC3D), debido a que la primera tenia una buena fiabilidad en casos de pacientes con MHF Grado I de Pruzansky, mientras que en pacientes Grado II la fiabilidad era baja, por lo que el uso de TC3D era preferible. (41) Otra herramienta utilizada en pacientes con MHF es la fotogrametria, que permite una aproximacion no invasiva en la planificacion quirurgica. (42)

Los protocolos fotograficos tambien son utiles durante el diagnostico del paciente y en la evaluacion de los avances del resultado postratamiento. Un estudio publicado en 2013 por Birgfeld y colaboradores (43) arrojo que era factible establecer el fenotipo de pacientes con MHF tanto con imagenologia 2D como con 3D, las cuales presentaban diversas ventajas y desventajas. La fortaleza de las tecnicas 2D consistia en que para los clinicos era mas facil trabajar debido a su familiaridad con ellas; mientras que su debilidad era que dependia mucho de la cooperacion del paciente y de las habilidades del fotografo; ademas, no se podia girar y se necesitaba estandarizar correctamente las fotografias, debido a que las leves inclinaciones dificultaban determinar correctamente el grado de asimetria. La ventaja de las imagenes en 3D era que permitia girar las imagenes y ver el aspecto facial desde distintos angulos; ademas era mas rapido que seguir un protocolo fotografico. Su principal desventaja era la falta de definicion a nivel del oido y los parpados, y la interferencia del pelo, lo que se traducia en perdida de informacion.

Diagnostico diferencial

* Hipoplasia hemimandibular con colapso condilarcoronoideo: cuadro generalmente no diagnosticado al nacimiento, sin alteraciones de tejidos blandos y caracterizado principalmente por desviacion del menton por hipoplasia del condilo, proceso coronoides y rama mandibular, siempre en presencia de fosa temporal (cavidad glenoidea). (44,45)

* Sindromes: La MHF, al ser clinicamente variable, debe ser descartada por un genetista de sindromes que comprometen tambien el macizo maxilofacial. Sindromes como Treacher-Collins, Miller-Dieker, Townes-Brocks, CHARGE, branquio-oto-renal, Parry-Romberg, entre otros, presentan caracteristicas similares a la MHF, como alteraciones mandibulares, colobomas o alteraciones palpebrales y malformaciones del oido externo. (3)

Tratamiento

En general, se acepta que la mejor forma de tratar a pacientes con MHF es a traves de equipos interdisciplinarios, (46) cuya diversidad de especialidades permita, a traves de un trabajo conjunto, el tratamiento apropiado para cada paciente acorde a sus necesidades.

La planificacion del tratamiento se hara dependiendo del tipo de malformacion y la severidad en la expresion de esta, siempre tomando en cuenta las expectativas del paciente y la familia en cuanto a los resultados.

Con el tratamiento, principalmente de cirugia ortognatica/plastica y ortodoncia, se debe buscar mejorar la funcionalidad, junto con una simetria facial optima, con el fin de:47, 48

1. Aumentar el tamano del lado mandibular afectado y su tejido blando asociado.

2. Crear una articulacion que simule la ATM en los casos en los que esta este ausente.

3. Corregir deformidades secundarias en el maxilar.

4. Establecer una oclusion funcional, asi como una apariencia estetica facial y dentaria.

5. Mejorar y horizontalizar el plano de oclusion.

6. Obtener apertura bucal cuando esta se presenta limitada.

El tratamiento ortodontico convencional puede comprender inicialmente aparatologia funcional con el uso de activadores rigidos de acrilico, individualizados segun el caso. Estos aparatos permiten la expansion del tejido afectado, aprovechando el crecimiento fisiologico del paciente. En ocasiones pueden tener planos de altura en el lado sano, permitiendo la compensacion vertical de la zona afectada, siempre teniendo presente mantener centrada la linea media facial con la dentaria. Posteriormente se puede complementar con ortodoncia fija convencional.

Tratamiento quirurgico mandibular

Si bien la literatura es amplia en cuanto a tecnicas y tiempos quirurgicos, el tratamiento de los pacientes con MHF se puede dividir en dos grupos, segun la clasificacion de Kaban-Prusansky: los pacientes Grado I y Grado IIA se tratan de la misma forma, mientras que los pacientes Grado IIB y Grado III se tratan de manera similar entre ellos, pero distinta al primer grupo. (49) (tabla 2).

El manejo quirurgico mandibular es esencial, y la distraccion osea mandibular tiene diversas ventajas sobre el injerto costocondral. Entre ellas esta aumentar el largo vertical de la mandibula, mejorar la asimetria del tejido blando, producir menor perdida de sangre, tener un mejor control del vector de avance y obtener una mejora sustancial en la biomecanica de la mandibula. (50)

Mandibular surgery

While the literature is broad in terms of techniques and surgical times, the treatment of HFM patients can be divided into two groups, according to the classification by Kaban-Prusansky: Grade I and Grade IIA patients are treated in the same way, while Grade IIB and Grade III patients are treated similarly among them but different to the first group. (49) (table 2).

Surgical management of the mandible is essential, and mandible bone distraction has several advantages over costochondral graft. These include: increase mandible vertical length, improve asymmetry of soft tissue, produce less blood loss, have better control of progress vector, and obtain a substantial improvement in the biomechanics of the lower mandible. (50)

Grado de MHF (Kaban)

Procedimiento quirurgico

La distraccion osea se basa en el principio de tension-estres para permitir el alargamiento oseo y de tejidos blandos a partir de la separacion controlada de segmentos oseos (figura 3). Para ello existen diversos tipos de distractores, los cuales se pueden categorizar en dos areas. De acuerdo a su ubicacion, los distractores pueden ser extraorales e intraorales; mientras que, segun la cantidad de vectores con los cuales trabajan, estos pueden ser univectorial o unidireccional, o bidireccional (plano horizontal y vertical) o multidireccional (plano horizontal, vertical y transversal). (51)

En las imagenes se observan las ortopantomografias de una paciente de 3 anos de edad con MHF tipo II durante la distraccion osea con aparato extraoral. La imagen A corresponde a la radiografia inicial. La imagen B corresponde a la radiografia de control una vez instalado el distractor. La imagen C se tomo luego de un mes de distraccion. Notese el cambio de inclinacion del distractor, el aumento en la simetria mandibular y la mejor relacion de las piezas dentarias.

La eleccion del aparto de distraccion dependera de diversos factores, entre ellos la edad del paciente, el grado de severidad de la malformacion y la necesidad de movilidad de los segmentos. En general, los aparatos extraorales requieren una cirugia menos compleja, pueden lograr distancias de distraccion mas largas y permiten manejar la distraccion en los tres sentidos del espacio, pero dejan cicatrices en la piel, son mas visibles y pueden llegar a ser mas pesados, presentando molestias para el paciente. Los aparatos intraorales son menos visibles y no dejan cicatriz facial, pero tienen un limitado rango de movilidad en el espacio, y su cirugia es mas compleja tanto para su insercion como para su remocion. Recientemente se han desarrollado dispositivos reabsorbibles que permiten la distraccion mandibular en una etapa, logrando avances de entre 15 y 30 mm. (52) De todas formas, la simulacion quirurgica en un modelo solido puede ayudar a lograr mejor simetria mandibular, especialmente en distraccion osea con multivector. (53)

Es importante recalcar la necesidad de tomar en cuenta, mas alla del estadio del crecimiento del paciente, las necesidades de tratamiento que este tiene, ya que varian entre los pacientes, y por tanto cada caso debe ser analizado como unico.

Complicaciones

Una revision de la literatura en 200954 comparo la estabilidad y las complicaciones de la distraccion osea y el injerto costocondral. Encontro que ambas tecnicas tienen una tasa de recidiva similar cuando se realiza un avance mandibular de entre 6 y 10 mm. Las principales complicaciones se muestran en la tabla 3. Dicha revision, si bien sugiere que la distraccion osea mandibular es menos susceptible a grandes complicaciones, es blanco de complicaciones menores que tambien causan morbilidad en el paciente, ademas de estar afectada por otros factores como la larga fase de consolidacion, el costo del distractor, el cumplimiento del paciente en activar el distractor y la necesidad de realizar una segunda cirugia para extraer el distractor.

Otras cirugias

Al ser una malformacion con gran variacion fenotipica, los pacientes con MHF pueden necesitar otras cirugias, dependiendo de las estructuras comprometidas. Una revision de la microsomia craneofacial realizada por Birgfeld y Heike en 2012 (55) muestra una linea de tiempo como guia en el manejo medico-quirurgico de los pacientes con MHF, propuesta por los miembros del Centro Craneofacial en el Hospital de Ninos de Seattle, contemplando su avance desde el nacimiento hasta la adultez. Dependiendo del paciente, puede ser necesario realizar:

Orbita: Puede involucrar cirugias de dermoides epibulbares y coloboma del parpado. En casos de alteraciones en tamano o posicion de la orbita, la reposicion se realiza alrededor de los 3 o 4 anos de edad.

Oidos: Tubos de ventilacion timpanica (colleras). En caso de alteracion del oido externo, la cirugia varia de acuerdo al compromiso del pabellon auricular, desde la remodelacion del cartilago en caso de hipoplasias leves, hasta la reconstruccion completa a traves de injertos autologos o aloplasticos, como el polietileno poroso de alta densidad. En pacientes con perdida auditiva, se debe evaluar la posibilidad de reparacion de atresia del canal auditivo.

Nervio facial: En casos de paralisis del nervio, se debe evaluar la zona y el grado de compromiso, que puede ser superior (afecta a la zona temporal y cigomatica), inferior (zona bucal, mandibular y cervical) o total. En caso de compromiso bucal, se debe evaluar la necesidad de realizar reanimacion facial. En caso de alteracion del movimiento palpebral, se debe considerar algun tipo de tratamiento con el fin de evitar queratitis corneal por exposicion.

Tejidos blandos: Cierre de fisuras orofaciales, correccion de via aerea, cirugia de aumento de tejidos blandos e injertos de grasa.

En Chile no existen protocolos de tratamiento publicados para la microsomia hemifacial, patologia que tampoco esta cubierta por el sistema publico de salud, por lo que la mayoria de los pacientes realiza sus tratamientos en forma privada, siendo condicionados por diversos factores como el acceso a especialistas con conocimiento en MHF, costo de los procedimientos, prevision de salud, entre otros.

En Latinoamerica solo existe un protocolo de seguimiento, (56) publicado en Argentina, pero no existe ningun protocolo de tratamiento.

CONCLUSIONES

La microsomia hemifacial es una enfermedad heterogenea, variable y de expresividad unica en cada sujeto, tanto en su etiologia, como en su severidad y por ende en su tratamiento. Al ser una alteracion en espectro, afecta diversas estructuras del individuo de acuerdo a su gravedad. Es por ello que en estos pacientes es de vital importancia el trabajo interdisciplinario muy bien coordinado, ya que pueden presentar incluso alteraciones psicosociales y extracraneales, que deben ser exploradas y tratadas a tiempo.

CONFLICTOS DE INTERES

Los autores declaran no tener ningun conflicto de interes.

CORRESPONDENCIA

Sebastian Veliz Mendez

(+5698) 166 6719.

sebastianvelizm@gmail.com.

Avenida La Paz No. 750, 2. piso, Oficina de Unidad de Malformacion Craneofacial

Santiago, Chile

SEBASTIAN VELIZ M [1], PAMELA AGURTO V. [2], NOEMI LEIVA V. [3]

[1] Cirujano dentista, Estadia en la Unidad de Malformacion Craneofacial, Facultad de Odontologia Universidad de Chile.

[2] Ortodoncista. Hospital Luis Calvo Mackenna, Chile.

[3] Profesor Asistente. Facultad de Odontologia Universidad de Chile. Ortodoncista. Hospital Luis Calvo Mackenna, Chile.

RECIBIDO: DICIEMBRE 3/2013--ACEPTADO: SEPTIEMBRE 15/2015

Leyenda: Figura 1. Diversidad de manifestaciones de la microsomia hemifacial

Figure 1. Diverse manifestations of hemifacial microsomia

Leyenda: Figura 2. Ortopantomografias de pacientes con microsomia hemifacial

Figure 2. Orthopantomograph of hemifacial microsomia patients

Leyenda: Figura 3. Distraccion osea en paciente con microsomia hemifacial Grado II

Figure 3. Bone distraction in patient with Grade II hemifacial microsomia
Tabla 1. Principales sistemas de clasificacion de pacientes con
microsomia hemifacial

A. Clasificacion de Pruzansky (21)

Grado I       Hipoplasia minima mandibular con todas las estructuras
                                    presentes.

Grado II     Condilo, rama y escotadura sigmoidea presentes, pero con
                      grosera alteracion en forma y tamano.

Grado III      Rama mandibular puede estar reducida a una pequena y
                      delgada lamina de hueso, o no existir.

B. Clasificacion de Pruzansky modificada por Kaban (22)

I                  Mandibula de morfologia normal pero pequena.

IIA         Rama mandibular corta de tamano anormal, cavidad glenoidea
                        en adecuada posicion y funcional.

IIB            Cavidad glenoidea en posicion alterada, en posicion
                           inferior, medial y anterior.

III              Ausencia de articulacion temporomandibular (ATM)

C. OMENS (23)

O: Asimetria de la orbita (Orbit)

O0                    Orbita con tamano y posicion normales.

O1                          Tamano orbitario anormal.

O2             Posicion orbitaria anormal (colocar una flecha de la
              posicion, ej.: O2 [flecha superior] si es superior, O2
                        [flecha inferior] si es inferior).

O3                    Posicion y tamano orbitario anormales.

M: Hipoplasia mandibular (Mandible)

M0                              Mandibula normal.

M1            La mandibula y la fosa glenoidea son pequenas, con una
                                   rama corta.

M2A            La fosa glenoidea tiene una posicion anatomicamente
                    aceptable con referencia a la ATM opuesta.

M2B          La ATM esta desplazada inferior, medial y anteriormente,
M3           con un condilo severamente hipoplasico. Existe ausencia
                     completa de rama, fosa glenoidea y ATM.

E: Deformidad en el oido externo (Ear)

E0                                Oreja normal.

E1              Hipoplasia leve, pero todas las estructuras estan
                                    presentes.

E2              Ausencia del canal auditivo externo con hipoplasia
                              variable de la concha.

E3              Lobulo mal posicionado, con ausencia de oreja. El
            remanente lobular generalmente esta desplazado inferior y
                                  anteriormente.

N: Compromiso de los nervios (Nerve)

N0                   No existe compromiso del nervio facial.

N1           Compromiso superior del nervio facial (ramas temporal y
                                   cigomatica).

N2             Compromiso inferior del nervio facial (ramas bucal,
                              mandibula y cervical).

N3            Todas las ramas del nervio facial estan afectadas. Se
               pueden analizar otros nervios comprometidos, como el
            trigemino N V (sensorial), el hipogloso N XII, y al resto
               de los nervios craneales se los anota con su propio
                                     numero.

S: Deficiencia en tejido blando (Soft tissue)

S0           No existe deficiencia de tejidos blandos ni deficiencia
                                    muscular.

S1             Deficiencia minima de tejidos blandos y deficiencia
                                 muscular minima.

S2                  Moderada--entre los dos extremos, S1 y S3.

S3          Severa deficiencia de tejidos blandos debida a hipoplasia
                   del tejido celular subcutaneo y del musculo.

Tabla 2. Procedimiento quirurgico de acuerdo al tipo de microsomia
hemifacial segun la clasificacion de Kaban, segun Liu y
colaboradores, 2012 (49)

Grado       Alargamiento vertical mandibular (osteotomia
I y IIA                   e injerto) (SSMO)

                 Distraccion osea mandibular (vector
                vertical). Rama corta verticalmente.

Grado IIB     Injerto oseo de la rama y el condilo, con
                reconstruccion de cavidad glenoidea.

              Distraccion osea mandibular (DMO) (vector
                   oblicuo). Rama corta vertical y
                          horizontalmente.

Grado III     Injerto oseo de la rama y el condilo, con
              reconstruccion de cavidad glenoidea para
                         crear ATM funcional

            Distraccion osea mandibular (vector oblicuo)
                           e injerto oseo.

Tabla 3. Posibles complicaciones de la osteotomia bilateral sagital
de rama y de la distraccion osea mandibular

Procedimiento   Complicaciones

                Recaida   Temprana   Deslizamiento de la osteotomia.
                                     Hundimiento condilar sin
                                       contacto.
                          Tardia     Remodelado o reabsorcion del
                                       condilo.

BSSO            Alteraciones en el nervio alveolar inferior.

                Alteraciones temporomandibulares. Crecimiento y
                reabsorcion impredecible. Falta de tejido blando y de
                irrigacion vascular en la zona.

                Mordida abierta anterior.

                Quiebre o mal funcion del distractor.

DMO57           Incumplimiento del paciente en la activacion y en los
                cuidados.

                Infeccion.

                Ulceras en labio inferior por presion del distractor.
                En el caso de DMO temprana, solo se indica en casos de
                obstruccion severa de la via aerea, debido a la
                limitacion mostrada en el tiempo de mantenerse
                estable. (58, 59)


HEMIFACIAL MICROSOMIA. A LITERATURE REVIEW

INTRODUCTION

Hemifacial microsomia (HFM) corresponds to a spectrum of congenital craniofacial malformations characterized by hypoplasia of tissues embryologically originating from the first and second branchial arches. Its expression is highly variable, even with defects of heart, spine, and central nervous system.

It is the second most common craniofacial malformation after cleft lip and palate, with an estimated incidence of 1/5,600 births. (1) It appears one-sided in 70% of cases, and its bilateral form is usually asymmetrical, affecting one side more than the other. (2)

As a complex heterogeneous alteration, patients showing its wide manifestations have received various diagnoses, such as Goldenhar Syndrome, oculo-auriculo-vertebral spectrum, syndrome of the first and second branchial arches, craniofacial microsomia, and among others. There are no common diagnostic criteria for this disorder yet. (3)

Its pathogenesis responds to a heterogeneous character explained by different theories. (4) One of them has been suggested by Poswillo, who claims that the cause would be a vascular disruption causing bleeding during embryologic formation of the stapedial artery, accompanied with alterations in the development of the first and the second branchial arches. The size of hematoma and the resulting tissue injury would explain the morphology and different variations of HFM in experimental models, since the larger in size the larger the alterations in the development of branchial arches. (5) Another theory has been postulated by Johnston, (6) who claims that the causal factor would be an alteration in the migration of cells of the neural crest towards the formation of the trigeminal ganglion. This lack in migration, and therefore the absence of interaction between mesenchyme and neural crest cells, has been associated with other problems observed in HFM patients, such as microdontia and hypodontia, (7) cleft palate and heart problems. (8)

Other authors suggest this relationship between lack of migration of cells of the neural crest and HFM because in the absence of these cells there is less vascular endothelial growth factor (VEGF). This growth factor promotes the proliferation of Meckel cartilage, and the absence of VEGF creates a correlation with mandibular hypoplasia. (9)

While its etiology is still unknown, various environmental and genetic factors have been recognized. Within the environmental causes, there are various risk factors associated with its presence during pregnancy, such as vasoactive medications, (10) vaginal bleeding during the second quarter, multiple gestations, (11) use of assisted reproductive technology by the mother (12) and preexisting or gestational diabetes. (13, 14)

M. Werler has published several studies on the relationship between HFM and the consumption of vasoactive drugs by the mother during pregnancy. One of them is a retrospective study of cases and controls discussing several factors to which the mother is exposed to during pregnancy, including vasoactive drugs such as pseudoephedrine, phenylpropanolamine, aspirin, and ibuprofen. The use of vasoactive medication in the first quarter, particularly in combination with smoking, was found to be associated with an increase in the risk of HFM; other factors were also associated, such as multiple gestations, diabetes, bleeding during the second quarter, and intensive alcohol consumption. (15)

Within the genetic causes, even though most cases are sporadic, in some cases there has been an autosomal dominant genetic component (associated with chromosome 14), (16, 17) an autosomal recessive component, (18) and chromosomal alterations, mainly in chromosomes 5 (5p deletion), 18 (trisomy) and 22 (22q11.2 deletion), among others. (19, 20)

Classifications

The classifications used in HFM patients have evolved over time, covering more pathological aspects each time.

1. Classification system of Pruzansky (1969)

The first classification used in HFM patients was done by Samuel Pruzansky in 196921 using x-rays of the jaws of patients with this condition. In its classification, Pruzansky observed three types of mandibular hypoplasias, from a relatively full mandible (Grade I) to one very small and whose deformity worsened over time (Grade III) (table 1-A). This classification includes only the description of the mandible, therefore, when used in HFM patients, it leaves out many aspects of the pathology.

2 Pruzansky's classification modified by Kaban et al (1988)

In 1988, Kaban et al (22) changed Pruzansky's classification by adding the description of deformations seen in temporomandibular joint teleradiography. The greatest difference appears in Grade II, which presents two sub-classifications depending on position of the glenoid cavity, which may be normal (IIA) or altered (IIB) (table 1-B).

3 OMENS (1991)

Given the abundant phenotypic variability of this malformation, in 1991 the OMENS classification was proposed (23) based on three criteria, considering that an HFM classification should be inclusive and versatile, that the anatomic components should be separately analyzed, and that data should be expressed in a numerical scale to make them clinically useful. The OMENS abbreviation corresponds to its acronym for the five main manifestations of HFM: O: asymmetry of the orbit (Orbit); M: mandibular hypoplasia (Mandible); E: Deformity in the outer ear (Ear); N: Nerve involvement (Nerve); S: Deficiency in soft tissue (Soft Tissue) (table 1-C).

3.1 Amendments to the OMENS

* OMENS+ (1995): It was postulated in order to expand the phenotypic expression of HFM patients to extracranial alterations. (24)

* Graphic representation of the OMENS+: a graphic representation of the OMENS+ was introduced in 200725 and later modified in 2011, (26) in order to facilitate its understanding in clinical practice, teaching and the standardization of classification of HFM patients.

4. CFDS (Craniofacial Deformity Scoring) (27) (2001)

This corresponds to the sum of MDS (Mandibular Deformity Scoring) + CDS (Cranial Deformity Scoring). Through the use of computed tomography, different bone structures are analyzed and assigned values according to the extent to which they are involved; the maximum values are 16 points for MDS and 19 for CDS.

Clinical features

As this is an anomaly of the first and second branchial arches, most alterations are associated with structures developed from these arches, (28) presenting wide phenotypic variation. The following structures are involved:

* Jaw and TMJ: asymmetrical mandibular development for hypoplasia, absence of mandibular structures (condyle and ramus), absence or ankylosis of temporomandibular joint (TMJ). Recently published studies showed that HFM patients presented both mandibular and maxillary retrusion in comparison with the control group, along with an increase in the vertical component; these patterns were more marked in the affected side and increased according to severity. (29) Mandibular height was always lower along growth, but the growth pattern was similar in both groups. (30) In terms of TMJ, it has been observed that the degree of mandible dysplasia does not correspond to the degree of disk dysplasia, which vary among individuals; while the unaffected side does not present major alterations. (31)

* Orbit: orbit dystopia (bad position), epibulbar dermoid, anophthalmia/microphthalmia, blepharoptosis, retinal or choroidal coloboma, among other less frequent anomalies. (32)

* Ears: microtia, anotia, loss of hearing, disorders of the middle ear.

* Cranial nerves: involvement of facial nerve and, in more severe cases, of the trigeminal and hypoglossal nerves.

* Dental: agenesis, (7) dental hypoplasias, (33) microdontia, and malocclusions. Delayed tooth development in HFM patients type IIB and III, (34) with the most alterations in posterior teeth. (35)

* Maxillofacial: labio-palatal fissure, (36) macrostomia, hypoplasia of the facial thirds, occlusal plane inclination (highly variable in angle), hypoplasia of masticatory muscles, (37) velopharyngeal insufficiency. (38)

* Extracranial changes: primarily in kidney, lungs, heart, gastrointestinal, skeletal, and central nervous system (CNS). (24)

Because of this, it is necessary to establish the degree of involvement of the affected structures, both anatomically and functionally, in order to make timely referrals to the specialists in each of the involved areas. (figure 1).

The photographs show patients with varying degrees of HFM. In image A, the patient presents a Grade I mandibular disorder, with slight deviation of the lower third. Image B corresponds to a Grade IIA alteration, presenting alteration of symmetry, both at the lower third and the orbits. Image C shows an alteration of the lower third, with full involvement of the right auricle, corresponding to a patient with a Grade IIB anomaly. Image D corresponds to a patient with a Grade III alteration of the left side.

Other aspects studied in HFM patients refer to an increased frequency in internalizing problems, poor social skills, and less acceptance by pairs--most commonly observed in women with young mothers at birth and additional alterations besides the mandibular--. (39) An increased frequency of snoring and other sleep disorder symptoms has also been observed. (40)

Although diagnosis is mainly clinical, various complementary tests allow a better analysis of this pathology. Panoramic radiography (figure 2) allows an initial analysis of the structures of mandibular and maxillofacial structures, evaluating both sides in the same image. A profile teleradiography allows evaluating, through cephalometric analysis, the relations between maxilla and mandible, while front teleradiography allows observing the degree of asymmetry and mandibular deviation. An occlusal x-ray offers a clear view of the palatal vault in case of labio-palatal fissure.

These images show radiographs of HFM patients, all on the right side but with varying degrees of severity (Image A: Grade I; image B: Grade II, image C: Grade III). It can be observed that as severity increases, the symmetry between the rami and other jaw structures reduces, with total condyle loss in picture C.

An alternative way of evaluating HFM is through TC3D. While it allows a more realistic and detailed view, this technique requires applying a large amount of radiation on patients. A study by Takahashi et al in 2013 suggests careful use of both methods (panoramic radiography and TC3D), since the first had good reliability in cases of HFM patients in Grade I of Pruzansky, while reliability was low in Grade II patients, so the use of TC3D was preferable. (41) Another tool used in HFM patients is photogrammetry, enabling a noninvasive approach in surgical planning. (42)

Photographic protocols are also useful in diagnosis and in evaluation of post-treatment advances. A study published in 2013 by Birgfeld et al (43) showed that it was feasible to establish the phenotype of HFM patients with both 2D and 3D imaging, which had several advantages and disadvantages. The strength of the 2D techniques was that clinicians find them easier to handle due to familiarity with them, while their weakness was that they were highly dependable on patient cooperation and photographer skills; in addition, they could not be rotated and needed proper photograph standardization, since slight inclinations made it difficult to correctly determine the degree of asymmetry. The advantage of 3D images was that they allowed rotating images and seeing the facial appearance from different angles; it was also faster to follow than a photographic protocol. Their main disadvantage was the lack of definition at the level of ear and eyelids, and hair interference, which resulted in loss of information.

Differential diagnosis

* Hemimandibular hypoplasia with condylarcoronoid collapse: a condition not usually diagnosed at birth, with no soft tissue alterations and mainly characterized by chin deviation for hypoplasia of condyle, coronoid process, and mandibular ramus, always in the presence of temporal fossa (glenoid cavity). (44, 45) * Syndromes: being a clinically variable condition, HFM mustbe discarded by ageneticist of syndromes involving the maxillofacial complex. Syndromes such as Treacher-Collins, Miller-Dieker, Townes-Brocks, CHARGE, branquio-oto-renal, Parry-Romberg, among others, have similar characteristics to HFM, such as mandibular disorders, colobomas or eyelid malformations and abnormalities of the outer ear. (3)

Treatment

In general, it is accepted that the best way to treat HFM patients is through interdisciplinary teams (46) whose diversity of specialties allows, through a joint effort, the appropriate treatment for each patient according to individual needs.

Treatment planning depends on type of malformation and severity in its expression, always taking into account patient and family expectations in terms of the results.

Mainly through plastic/orthognathic surgery and orthodontics, the treatment seeks to improve functionality, along with optimum facial symmetry, in order to: (47, 48)

1. Increase the size of the affected mandibular side and its associated soft tissue.

2. Create a joint simulating the TMJ in cases where it is absent.

3. Correct secondary deformities in maxilla.

4. Achieve functional occlusion, as well as aesthetic facial and dental appearance.

5. Improve and horizontalize the occlusal plane.

6. Achieve mouth opening if it is limited.

Conventional orthodontic treatment may initially include functional appliances with the use of rigid acrylic activators, which are individualized according to each case. These devices allow for expansion of affected tissue, taking advantage of patient's physiological growth. Sometimes they can have height planes on the healthy side, allowing for vertical compensation of the affected area, always bearing in mind that facial midline should be centered with tooth midline. This can later be complemented with conventional fixed orthodontics.

Bone distraction is based on the principle of tension-stress to allow elongation of bone and soft tissue from the controlled separation of bone segments (figure 3). There are different types of distraction, which can be classified into two areas. According to location, distractors can be extraoral and intraoral; while, according to the amount of vectors with which they work, they can be univectorial or unidirectional or bi-directional (horizontal and vertical plane) or multidirectional (horizontal, vertical and transversal plane). (51)

Orthopantomographs of a 3-year-old patient with Grade II HFM during bone distraction with headgear. Image A corresponds to the initial x-ray. Image B corresponds to control x-ray after the distractor had been installed. Image C was taken one month after distraction. Note the change in distractor inclination, the increase in mandibular symmetry and the improved teeth relations.

The choice of distraction appliance depends on various factors, including patient's age, the degree of malformation severity and the need for mobility of segments. In general, extraoral appliances require a less complex surgery, can achieve longer distraction distances, and allow handling the distraction in the three directions of space, but they leave scars on the skin, are more visible, and may be heavier, presenting patient discomfort. Intraoral devices are less visible and don't leave facial scars, but have a limited range of motion in space, and their surgery is more complex for both insertion and removal. Re-absorbable devices have recently been developed, allowing for mandibular distraction in a single stage, and achieving progress of 15 to 30 mm. (52) In anyways, the surgical simulation in a solid model can help achieve better mandible symmetry, especially in bone distraction with multivector. (53)

It is important to stress the need to take into account, besides patient's growth state, his or her treatment needs, since they vary among patients, and therefore each must be analyzed as a unique case.

Complications

A 2009 literature review (54) compared the stability and complications of bone distraction and the costochondral graft. It found out that both techniques have a similar relapse rate when performing mandibular advancement of 6 to 10 mm. The main complications are shown in table 3. While this review suggests that mandibular bone distraction is less susceptible to major complications, it also points out the it may produce minor complications that also cause patient morbidity, in addition to being affected by other factors such as a long phase of consolidation, distractor cost, patient compliance in activating the distractor and the need for a second surgery to remove the distractor.

Other surgeries

Being a malformation with abundant phenotypic variation, HFM patients may need other surgeries, depending on the involved structures. A review of craniofacial microsomia performed by Birgfeld and Heike in 2012 (55) shows a timeline as a guide in the medical and surgical management of HFM patients, proposed by members of the Seattle Children's Craniofacial Center, monitoring its progress from birth to adulthood. Depending on patient, it may be necessary:

Orbit: It may involve surgeries of epibulbar dermoid and eyelid coloboma. In cases of changes in size or position of the orbit, the replacement is done around the age of 3 to 4 years.

Ears: Tympanic ventilation tubes (clamps).

In case of alteration of the outer ear, surgery varies according to the involvement of pinna, from remodeling cartilage in the event of slight hypoplasias to the complete reconstruction through autologous or alloplastic grafts, such as porous high-density polyethylene. In patients with hearing loss, the possibility of repairing atresia of the auditory canal should be evaluated.

Facial nerve: in cases of nerve palsy, the area and degree of involvement should be evaluated; this involvement may be upper (affects the temporal and zygomatic area), lower (buccal, mandibular and cervical area), or total. In the case of oral involvement, the need for facial reanimation should be evaluated. In case of alteration of eyelid movement, some type of treatment should be considered in order to prevent corneal keratitis by exposure.

Soft tissue: Closure of orofacial fissures, correction of airway, surgery of soft tissue augmentation, and fat grafts.

In Chile there are no published treatment protocols for hemifacial microsomia, a pathology that is not covered by the public health system, so most patients have their treatments in privet offices and therefore are conditioned by various factors such as access to specialists with knowledge in HFM, cost of procedures, or health prevision, among others.

In Latin America there is only one follow-up protocol (56) published in Argentina, but there is no treatment protocol.

CONCLUSIONS

Hemifacial microsomia is a heterogeneous, variable disease of unique expression in each subject, both in its etiology and severity and therefore in its treatment. Being an alteration of wide spectrum, it affects various structures of the individual according to its severity. This is why a very web-coordinated interdisciplinary work is vital in these patients, since they may even have psychosocial and extracranial alterations which should be timely explored and treated.

CONFLICTS OF INTEREST

The authors declare not having any conflict of interest.

CORRESPONDING AUTHOR

Sebastian Veliz Mendez

(+5698) 166 6719.

sebastianvelizm@gmail.com.

Avenida La Paz No. 750, 2. piso, Oficina de Unidad de Malformacion Craneofacial

Santiago, Chile

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SEBASTIAN VELIZ M [1], PAMELA AGURTO V. [2], NOEMI LEIVA V. [3]

[1] DDS, Intern in Craniofacial Malformation, Universidad de Chile School of Dentistry.

[2] Orthodontist. Hospital Luis Calvo Mackenna, Chile.

[3] Assistant Professor. Universidad de Chile School of Dentistry. Orthodontist. Hospital Luis Calvo Mackenna, Chile.

SUBMITTED: DECEMBER 3/2013--ACCEPTED: SEPTEMBER 15/2015
Table 1. Main classification systems of hemifacial microsomia patients

A. Classification of Pruzansky (21)

Grade I     Minimum mandibular hypoplasia with all structures present.

Grade II      Condyle, ramus and sigmoid notch are present, but with
                      serious alteration in shape and size.

Grade III    Mandibular ramus can be reduced to a small thin layer of
                             bone, or does not exist.

B. Classification of Pruzansky modified by Kaban (22)

I                   Mandibular morphology is normal but small.

IIA          Mandibular ramus is short but of abnormal size; glenoid
                     cavity in right position and functional.

IIB           Glenoid cavity is in an altered position, in inferior,
                          medial, and anterior position.

III                  Absence of temporomandibular joint (TMJ)

C. OMENS (23)

O: Asymmetry of the orbit (Orbit)

O0                     Orbit with normal size and position.

O1                            Abnormal orbital size.

O2           Abnormal orbital position (place a position arrow, e.g.:
               O2 [up arrow] for upper, O2 [down arrow] for lower).

O3                     Abnormal orbital size and position.

M: Mandibular hypoplasia (Mandible)

M0                               Normal mandible.

M1            The mandible and glenoid fossa are small, with a short
                                      ramus.

M2A         The glenoid fossa has an anatomically acceptable position
                       with reference to the opposite TMJ.

M2B         The TMJ is displaced in a lower, medial and anterior way,
                       with a severely hypoplastic condyle.

M3           There is a complete absence of ramus, glenoid fossa and
                                       TMJ.

E: Deformity in the outer ear (Ear)

E0                                 Normal ear.

E1               Mild hypoplasia, but all structures are present.

E2             Absence of the external auditory canal with variable
                             hypoplasia of the shell.

E3          Lobe poorly positioned, with absence of ear. Lobar remnant
              is generally moved towards a lower anterior position.

N: Nerve involvement (Nerve)

N0                    There is no facial nerve involvement.

N1          Upper involvement of facial nerve (temporal and zygomatic
                                      rami).

N2          Lower involvement of facial nerve (buccal, mandibular and
                                 cervical rami).

N3          All rami of facial nerve are affected. Other nerves can be
             involved, such as trigeminal NV (sensory), hypoglossal N
                XII, and the rest of cranial nerves with their own
                                     numbers.

S: Deficiency in soft tissue (Soft tissue)

S0               There is no deficiency of soft tissue nor muscle
                                   deficiency.

S1              Minimal soft tissue and minimal muscle deficiency.

S2                 Moderate--between both extremes, S1 and S3.

S3                      Severe soft tissue deficiency due
                 to hypoplasia of subcutaneous tissue and muscle.

Table 2. Surgical procedure according to hemifacial microsomia type
following the classification by Kaban, according to Liu et al,
2012 (49)

Degree of                  Surgical procedure
HFM (Kaban)

Grade I       Vertical mandible lengthening (osteotomy and
and IIA                       graft) (SSMO)

              Mandible bone distraction (vertical vector).
                         Ramus vertically short.

Grade IIB         Bone graft of ramus and condyle, with
                    reconstruction of glenoid cavity.

                Mandible bone distraction (MBD) (oblique
               vector). Ramus vertically and horizontally
                                 short.

Grade III         Bone graft of ramus and condyle, with
               reconstruction of glenoid cavity to create
                             functional TMJ.

               Mandible bone distraction (oblique vector)
                             and bone graft.

Table 3. Possible complications of bilateral sagittal osteotomy of
ramus and mandible bone distraction

Procedure   Complications

            Relapse   Early   Sliding of osteotomy.
                              Sinking of condyle without contact.
                      Late    Remodeling or resorption of condyle.

BSSO        Alterations in the inferior alveolar nerve.

            Temporomandibular disorders. Growth and
            unpredictable reabsorption. Lack of soft tissue
            and vascular irrigation in the area.

MDO (57)    Anterior open bite.

            Breakage or malfunction of distractor.

            Patient failure to activate and provide care.

            Infection.

            Ulcers in lower lip by pressure of distractor. In
            the case of early DMO, it is only indicated in
            cases of severe obstruction of airway, due to
            limitations to remain stable over time. (58, 59)
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Author:Veliz M., Sebastian; Agurto V., Pamela; Leiva V., Noemi
Publication:Revista Facultad de Odontologia
Article Type:Ensayo
Date:Jul 1, 2016
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