Chiari I Malformation: Clinical Presentation and Management.
Chiari I malformation is a herniation of the cerebellar tonsils into the foramen magnum. This herniation creates a crowding at the craniocervical junction. Clinical presentation of Chiari I malformation is highly variable. Radiographic and clinical criteria are utilized when determining the clinical significance of a patient's Chiari I malformation. Thus, timely recognition may be delayed if Chiari I malformation is not included in the differential diagnosis. Although the incidence of Chiari I malformation is unknown, it is not uncommon,is Therefore, a basic knowledge of Chiari malformations, their clinical presentations, and neurosurgical management issues is necessary for neuroscience nurses to provide optimal care and counsel to this patient population.
This article describes Chiari I malformation found in the adult, commonly associated syringohydromyelia (syrinx), presenting signs and symptoms, operative treatment, and nursing care. Chiari malformation types II-IV also are briefly described so that the differentiation can be appreciated.
In 1891, a German professor of pathological anatomy, Hans Chiari, wrote the paper "Concerning Alterations in the Cerebellum Resulting from Cerebral Hydrocephalus." Chiari described what is now known as a Chiari type I malformation as elongated, "pegged," cerebellar tonsils, displaced into the upper cervical canal. The hypothesis ascribing Chiari malformations to cerebral hydrocephalus was later proved wrong. Chiari's 1896 patient descriptions outlined three further degrees of cerebellar anomalies, which are now known as Chiari types II, III, and IV.
Neuroanatomy of the Foramen Magnum--An Overview
A complete discussion of the foramen magnum and the structures surrounding it is beyond the scope of this article. However, a brief overview of anatomical structures of the foramen magnum is warranted, so that the Chiari I malformation and its clinical effects can be better appreciated. The occipital bone surrounds the foramen magnum. The foraminal opening is oval-shaped, and it is wider posteriorly (Fig 1). The paired occipital condyles are lateral to the foramen magnum and articulate with the atlas. The alar ligaments attach the odontoid process to the medial side of each condyle and to the lateral masses of C1 (Fig 2). The atlas is ring-shaped and lacks a vertebral body and spinous process, making it different from all other vertebrae. The medial aspect of each lateral mass has a small tubercle for the transverse ligament to attach. The transverse foramen holds the vertebral artery. The vertebral arteries enter the dura behind the occipital condyles and ascend through the foramen magnum. The caudal part of the brainstem, cerebellum, and fourth ventricle, the rostral part of the spinal cord, and the lower cranial and upper cervical nerves are all located in the region of the foramen magnum (Fig 3).
Chiari Malformation Classification
Chiari I malformation consists of caudal displacement of the cerebellar tonsils into the upper cervical spinal canal, thus crowding the craniocervical junction. In type II malformations, the cerebellar vermis, brainstem, and the fourth ventricle extend through the foramen magnum. Type II malformations are almost always associated with myelomeningocele and hydrocephalus. Chiari III and IV malformations are rare. Chiari III malformation is the most severe form with cerebellar and brainstem tissue herniating through an upper cervical spina bifida forming an encephalocele. Type W is not considered by some to belong in the classification system because it is not a hindbrain herniation. It consists of cerebellar hypoplasia or aplasia. The only commonality among Chiari I-IV malformations is that they all involve the cerebellum. They have neither anatomic nor embryologic correlation. Table 1 compares Chiari I-IV malformations in terms of neuropathologic findings, clinical presentations and diagnosis, and treatment and outcomes.
Table 1. Indications, Diagnoses, Treatment, and Outcomes of Chiari Malformation, Types I-IV[13,18] Neuropathologic Clinical Presentation Treatment and Findings and Diagnosis Outcomes Chiari I * Caudal displacement * Typically present * If symptomatic of cerebellar tonsils with clinical symptoms hydrocephalus is into the cervical in young to middle present, canal, rarely below adulthood (35.9 ventriculo-peritoneal C2 [+ or -] 16.8) with a (VP) shunting is female preponderance done, usually * Associated syrinx alleviating most of in 65% of cases; is * Most common symptom patient's symptoms. most common in is pain (63%), cervical cord, but especially headaches * When hydrocephalus occasionally seen that increase with and basilar extending into more coughing, straining, invagination are distal cord exertion ruled out or treated, (Valsalva-inducing then a decompression * Hydrocephalus maneuvers). consisting of present in less than suboccipital 10% of cases * Three main patterns craniectomy with of clinical signs: duraplasty, C1 * Not usually laminectomy and associated with other 1. Brainstem possibly C2, C3 brain anomalies compression syndrome: laminectomy is done Ataxia, corticospinal to allow normal flow and sensory deficits, of CSF across the lower cranial nerve foramen magnum; palsies usually this procedure alone will 2. Central cord result in improvement syndrome (related to of the symptoms and syrinx): Dissociated resolve the syrinx. sensory loss of heat and pain, usually in * Rare mortality with chest or upper decompression extremities * Morbidity includes 3. Cerebellar bleeding, pharyngeal syndrome: Truncal and and vocal cord limb ataxia, dysfunction, nystagmus. On exam, meningitis, CSF upper greater than leakage, and lower extremity pseudomeningocele weakness with loss of formation. temperature and pain, usually in the * When a syrinx is cervical dermatomes. refactory despite the MRI is the diagnostic decompression method of choice procedure, then a because it can assess syrinx to the degree of subarachnoid space or herniation, determine syrinx to peritoneal if syrinx is present shunt may be and assess the attempted. response to surgical treatment. * The goal of surgical treatment is to stop symptom progression. Poor outcome is associated with long duration of symptoms or prior treatment. Chiari II * Inferior vermis, * Presentation most * Prior to medulla and fourth likely in neonate and decompression, the ventricle are child hydrocephalus must be caudally displaced treated with shunting into the cervical * In neonate, canal presentation often * Suboccipital accompanied by rapid craniectomy with * Myelomeningocele neurological cervical laminectomy present in deterioration related and dural patch essentially 100% of to brainstem grafting is treatment cases compression and of choice cranial nerve palsy. * Hydrocephalus * Technically present in most * Neonate may present challenging due to with dysphagia, poor highly variable * Associated with gag reflex, apneic anatomy multiple posterior spells, stridor and fossa and cerebral vocal cord paresis: * Surgical procedure anomalies often performed on 1. Brainstem seriously ill compression syndrome: neonates with Dysphagia, poor suck, medullary dysfunction aspiration * Outcomes in 2. Spinal cord cyst: newborns often poor Upper extremity due to other spasticity, neck pain, uncorrectable sensory loss (loss of anomalies temperature and pain) * Older children with * On exam, upper much better prognosis greater than lower after surgical extremity weakness treatment; most with with loss of complete or near temperature and pain, resolution of usually cervical symptoms dermatomal * Early recognition and prompt treatment is key Chiari III * Rare and most * Infants with this * Treatment often severe form anomaly are generally fraught with serious greatly neurologically technical and ethical * Displacement of compromised. dilemmas posterior fossa structure with * Often the anomaly * If surgery is cerebellum herniated may be incompatible undertaken, the sac through foramen with life. is excised and the magnum brain tissue is placed into the * Often with posterior fossa with encephalomeningocele dural graft and skin present (external sac coverage. containing brainstem and cerebellar components) Chiari IV * Many authors have * Surprisingly, many * No surgical therapy stopped including patients usually have this classification only mild to moderate since it is not a neurologic deficits. hindbrain anomaly. * Rather it is a very rare anomaly consisting of the cerebellar hypoplasia associated with a small posterior fossa. * Rare hydrocephalus
Radiographic Diagnostic Criteria and Associated Abnormalities
Chiari I malformation is a diagnosis made by radiographic criteria. Magnetic resonance imaging (MRI) is the diagnostic tool of choice.[3,4,19,24] The clinical significance of this diagnosis depends on the presenting signs and symptoms and, thus, degree of impairment and disability. The following criteria are used when radiographically determining the presence of a Chiari I malformation:[18,20,22]
* Caudal descent of the cerebellar tonsils at least 3-5 mm below the plane of the foramen magnum
* "Pegged or pointed" appearance of the tonsillar tips
* Crowding of the subarachnoid space in the area of the craniocervical junction.
Associated abnormalities primarily occur in the spinal cord and skeletal system. A syrinx is present in 20%-40% of all patients with Chiari I malformations. However, 60%-90% of symptomatic patients have a syrinx. A syrinx usually involves only the cervical spinal cord; however, occasionally it involves the entire cord.[18,22] (The section on syringohydromyelia provides further details.)
Skeletal anomalies occur in approximately 25% of patients with Chiari I malformations.[18,20,22] These include
* Basilar invagination (25%-50%)
* Klippel-Feil syndrome (5%-10%)
* Atlanto-occipital assimilation (1%-3%).
These craniovertebral anomalies are highly correlated with Chiari I malformations. Basilar invagination is a prolapse of the vertebral column into the skull base. Klippel-Feil syndrome is associated with assimilation of the atlas, fused vertebrae, and spinal anomalies. Clinically, the patient will have a short neck, low posterior hairline, and limited neck range of motion. Other congenital anomalies usually are present. Atlanto-occipital assimilation is failure of segmentation between the fourth occipital sclerotome and the first spinal sclerotome.
In addition, in a study of 50 patients with Chiari I malformation, Dyste found 57% had scoliosis, 57% had a shallow posterior fossa, and 51% had a widened spinal canal. Milhorat, in a large prospective study of 364 symptomatic patients with Chiari I malformation, found that 65% had associated syrinx, 42% had scoliosis, and 12% had basilar invagination.
Signs and symptoms are usually attributed to either syringohydromyelia, compression of the brainstem, or cerebellar compression. Dysfunction of the spinal cord due to syrinx constitutes a large percentage of the signs and symptoms.[1,16,18,20,21] Patients may complain of weakness, pain, and/or sensory disturbances, most commonly in one or both upper extremities. Signs include scoliosis, sensory loss, dysesthesias, wasting of the hands or arms, lower extremity spasticity, urinary incontinence, or weakness. Brainstem compression may lead to headache or neck pain, downbeat nystagmus, hoarseness, impaired gag reflex, dysphagia, hiccups, severe snoring, respiratory dysrhythmias, facial numbness, drop attacks, or dysarthria.[15,18,20] Cerebellar compression can lead to ataxia and nystagmus.[18,20] The most common presenting symptom is headache.[1,6,10,15,23,24,26]
Syringohydromyelia (syrinx) is a term that refers to a cystic cavity of the spinal cord. The most common underlying etiology of syrinx is a Chiari malformation. It also can be caused by spinal cord trauma or tumor. There are several theories that postulate how a hindbrain herniation causes these spinal cord cysts to form.[8,9,20,21] The theories all apply to the pathologic flow of cerebrospinal fluid (CSF) that occurs with hindbrain herniations. Recently, Heiss concluded the cerebellar tonsils act as a piston on the partially occluded subarachnoid space. This creates pressure waves that compress the cord and, with each heartbeat, sends syrinx fluid caudally. This eventually leads to syrinx progression. Therefore, the pathologic flow of CSF that occurs with a posterior fossa herniation often is resolved with decompression.[11,14,21,22]
Asymptomatic patients require no specific treatment. In these patients, the Chiari I malformation is found incidentally. If at some point the patient becomes clinically symptomatic, surgical intervention can be discussed. In a symptomatic patient, a suboccipital craniectomy, cervical laminectomy, and duraplasty to decompress the Chiari malformation is the treatment of choice.[2,16] The laminectomy and duraplasty provide space surrounding the cerebellum and spinal cord. This, in turn, allows for decreased pressure on the cerebellum and normalization of cerebral spinal fluid flow. Some clinicians also advocate the use of a stent if a large syrinx is present.[12,19,27] However, the syrinx usually resolves without placing a stent.[7,21] In our experience, if symptomatic hydrocephalus is present, a ventriculoperitoneal shunt is usually the initial step.
No neurosurgical procedure is without risks. The patient must have a clear understanding of the risks, benefits, and alternatives. Risks include neurological compromise, CSF leakage, infection, a chance that symptomatology would not improve, vocal cord or swallowing difficulties, or both, severe blood loss, anesthesia complications, and even death. The benefit of the procedure is improvement in neurological findings. In some circumstances, the anticipated benefit is to prevent further clinical deterioration. For instance, the surgical goal for a patient with myelopathy is to stop the patient from becoming more myelopathic, but improvement would not be expected. An alternative to surgery is to follow the patient with repeat MRIs, with careful attention to worsening symptomatology. In severe cases, there may be no appropriate alternative.
In our practice, a neurosurgery nurse practitioner (NP) is responsible for preparing the patient for surgery. Included is all patient education, the preoperative history and physical, preoperative diagnostic testing and followup of those diagnostic tests, and contact with the local physician as needed. The NP collaborates with the anesthesia screening clinic to ensure the patient is medically ready to undergo the operation.
Preoperative patient education includes providing procedure-specific as well as general surgical information. The more prepared patients are for their procedure, the more they are able to actively participate in their care. Adequate preoperative instruction also prevents miscommunication and false expectations. Our patients are given a patient educational handout, Health Facts for You, on Chiari I malformation, as well as a patient educational book on having surgery at this institution.
The Operative Procedure
The operative procedure usually recommended for patients with a Chiari I malformation and syrinx would be a suboccipital decompression with a cervical laminectomy and duraplasty. Once in the operating room, the patient is placed in a supine position for intubation, then given a standard preoperative dose of antibiotics, 1 gm of intravenous (IV) cefazolin, at our institution. If allergic to penicillin, the patient is given IV vancomycin 1 gm. The patient is then placed in a three-point head holder and rotated into the prone position. All appropriate padding is added and further positioning is completed; the back of the head is shaved, prepped, and draped in sterile fashion.
A midline incision is made from approximately the inion down to the spinous process of C2. The incision is carried through the midline dorsal cervical fascia and paraspinal musculature until the occipital bone is encountered. A subperiosteal plane is created along this bone to raise the paraspinal musculature and tendon attachments laterally. As the incision deepens and proceeds more inferiorly, the spinous process of C2 is identified and musculature cleared off along its superior edge. The posterior arch of C1 is identified, and the dissection is carried down to this structure. The suboccipital skull, posterior arch of C1, spinous process and lamina of C2 are cleared of soft tissue. Burr holes are placed in the suboccipital region. The occipital bone is removed from the posterior aspect of the foramen magnum. The opening of the foramen magnum proceeds laterally in both directions until the occipital condyles are encountered and the posterior fossa defect is approximately 3.5 to 4.0 cm. Working more inferiorly, a plane is created between the dura in the posterior arch of C1 along its anterior cortical edge. The posterior arch of C1 is then removed. A more extensive laminectomy may be required and is contingent on the level of the cerebellar tonsils.
The dura is opened in an Y-shaped fashion, and the tonsils are identified. Usually the tonsils are indented bilaterally and oftentimes are obviously impacted behind the posterior arch of C1. The tonsils may be spread apart using blunt dissection, and the fourth ventricle is entered through the median aperture. The region of obex is explored for arachnoid adhesions, and this region is taken down sharply in order to allow free communication of the fourth ventricle with the subarachnoid space of the cervical spine. Copious irrigation should be used to flush out any bleeding that has tracked down into the intradural cavity. A piece of dural graft is then fashioned to fit within the dural defect. This is then sewn into place with continuous running sutures. The grafting material may be Gore-Tex, fascia lata, or pericranium. The wound is then closed. The patient is turned back to a supine position. The head holder is removed, and the patient is awakened, extubated in the operating room, and transferred into the recovery room.
Typically, patients are monitored in either the neurosurgical intensive care unit or the intermediate care unit for 1 night. Postoperative patients receive neurological checks with vital sign monitoring every hour for the first 8 hours. The lower brainstem is close to the operative site. If complications develop, there is a high probability they will be exhibited in lower cranial nerve (CN) dysfunction. For example, dysfunction of CNs IX and X (glossopharyngeal and vagus) would affect gag and swallowing. Hypotension also might be exhibited. Dizziness, nystagmus, and difficulty hearing would indicate CN VIII (acoustic) dysfunction. Respiratory depression and apnea also are associated complications; respiratory status must be closely monitored. As always, it is extremely important to know the patient's preoperative baseline neurologic status.
Headache and posterior neck pain are expected and can be managed with either IV hydromorphone or morphine via patient-controlled analgesia. Usually by the second postoperative day, oral narcotics are tolerated. The narcotic strength needed is extremely variable. It can range from acetaminophen with hydrocodone to oxycodone, one to two pills every 4 to 6 hours. By 2 weeks postoperatively, many patients will require narcotics only at bedtime. As with all postoperative pain management, it needs to be patient-centered. The degree of pain after this surgery is greater than after a supratentorial craniotomy. Because of the large posterior cervical incision, there is a great deal of posterior neck pain and stiffness.
The dressing is observed for any sign of a CSF leak. The dressing is removed on postoperative day 3. Incision care takes place after dressing removal. The incision is left open to air, unless there is concern about CSF drainage. If there are no concerns, the patient may shower the following day (postoperative day 4). The shower should not beat on the incision, and the incision should not be submerged, as in a tub bath. After showering, the incision should be patted dry with a clean towel. Sutures typically are left in approximately 2 weeks. Incision care can vary by surgeon or institution.
Diet and Prevention of Constipation
If able to swallow safely, patients may have clear liquids the evening of surgery. Diet is advanced the next day as tolerated. If nausea and emesis are an issue, IV antiemetics are used. Constipation prevention is initiated when the patient is able to tolerate oral medications, because narcotic pain medications are extremely constipating. Docusate sodium along with a high-fiber, high-oral-fluid intake and activity will prevent most constipation problems. If constipation continues to be a problem, magnesium citrate can be purchased over the counter. Straining to defecate after this surgical procedure increases headache and causes general discomfort. It also can contribute to CSF leakage. Giving patients preprinted written instructions for avoiding constipation is extremely helpful.
Deep breathing with an incentive spirometer, when the patient is able to do so, should be done on an hourly basis. This promotes lung re-expansion and helps prevent atelectasis. Vigorous coughing also is avoided, as this may contribute to a CSF leak.
Deep Vein Thrombosis Prophylaxis
Thigh-high sequential compression stockings are placed in the operating room to prevent deep vein thrombosis (DVT). These are left on until the patient is ambulating on a regular basis. No other DVT prophylaxis is routinely used.
Physical therapy and occupational therapy are consulted only if the patient's neurological status warrants. In addition, a swallowing evaluation and subsequent speech and swallowing consultation are utilized, if indicated. If the patient has had significant preoperative symptomatology, a short inpatient rehabilitation course may be indicated.
Most patients are able to sit at the bedside the evening of surgery. Activity is getting up and out of bed on postoperative day 1 and gradually increasing the amount of walking. Increased activity also helps prevent constipation. After a Chiari I decompression, patients are instructed to avoid bending, straining, or lifting more than 10 lb for 6 weeks.
Discharge planning begins during the preoperative clinic visit. The patient's resources for home care after discharge need to be in place prior to undergoing surgery. The total hospital stay is typically 3 nights. Patients are not allowed to stay alone for several days following their procedure. In some circumstances, occupational or physical therapy may be consulted. They may not drive while on narcotics. Counsel your patients not to drive while their necks are too stiff to do so safely. Patients may be ready to return to sedentary work as soon as 2 weeks postoperatively. On the average, most people are not ready to return to work or school after 4-6 weeks. After a major neurosurgical procedure, postoperative healing needs to take place. Some patients have the advantage of being able to work from home or work a partial day. It is in the patient's best interest to have some agreement with his or her employer prior to surgery. Return to heavy-lifting occupations may not be until 8-12 weeks after surgery.
Discharge instructions also include observing the incision for any drainage or redness, tense fluid collection at the operative site, severe unrelenting headache, or fever greater than 101.5 [degrees] F, increasingly severe neck stiffness, or lethargy. If not contraindicated, nonsteroidal anti-inflammatory medications can be extremely effective for postoperative headache and neck stiffness. A postoperative MRI is obtained at 3 months if a syrinx was present. If signs and symptoms resolve, most do so by approximately 3 months, although there may be continued resolution for an extended time.
CH is a 19-year-old male who presented with acute onset, after sneezing, of persistent numbness and burning in his right shoulder, face, and neck area 3 months prior to seeing a spine surgeon. He also related that he experienced relatively severe headaches (typically located in the suboccipital and bifrontal regions) over the past several years. His headaches worsened with Valsalva maneuver and playing musical instruments. He denied any diplopia, swallowing problems, or gait abnormalities.
History and review of systems are as follows:
* Social history. On initial consultation, the family car was packed to take CH to college. He was planning to begin his freshman year. He is an active 19-year-old who exercises by running and weightlifting. He does not smoke or drink alcoholic beverages.
* Past medical history. Reye's syndrome, 1981
* Medications. He takes no medications.
* Allergies. He has no known drug allergies.
* Review of systems. Unremarkable.
On neurological examination, his pupils were equal, round, and reactive to light. Extraocular muscular movements were intact, without any vertigo or nystagmus. Mental status was normal. Speech was without evidence of dysarthria or aphasia. Strength was full throughout. Deep tendon reflexes were normal and symmetric throughout. Toes were downgoing. Sensory examination was intact to joint position, vibratory sensation, and light touch throughout. Decreased pinprick and temperature sensation were noted over the right face, side of neck, and shoulder. Intact temperature and pinprick were noted below the T1 level. Coordination and gait were normal. An MRI scan demonstrated a Chiari I malformation with syrinx in the cervical cord, which extended to at least the T3 level. There was no evidence of basilar invagination (Fig 4).
CH underwent a posterior fossa decompression and C1 laminectomy with duraplasty. He experienced significant postoperative nausea and vomiting; this was treated with antiemetics. He was discharged 4 days postoperatively. CH underwent a repeat MRI 4 months after his surgery. It showed complete resolution of the syrinx (Fig 5). He was neurologically intact and doing very well. CH had complete resolution of his symptomatology and was anxious to start college.
Chiari first described in 1891 an entity that is recognized today as Chiari I malformation. The radiographic diagnostic criteria used today are a mirror image of what Chiari described more than 100 years ago, even with our advanced technologic capabilities. Chiari I malformations often have an insidious onset. The patient may present with an array of symptoms that can cloud the diagnostic process. For symptomatic patients, a surgical decompression has a high probability of ameliorating their symptomatology. Heiss has shown that relieving the crowding from the cerebellar tonsils at the foramen magnum will take away the pulsatile CSF activity. Nursing involvement is pivotal in the care of this patient population. Neuroscience nurses are responsible for coordinating care and ensuring that patients are well informed about their plan of care. It is key to ensure that patients really understand their diagnosis, treatment plan, surgical procedure (if indicated), and postsurgical outcome expectations.
I would like to acknowledge my colleagues Jane Noyes, Joan Kutz, and Denise Brost who with me co-authored the original poster presentation for the 1997 Annual Meeting of the American Association of Neuroscience Nurses. My gratitude also goes to Dr. Gregory Trost and Dr. Bermans Iskandar for their thoughtful review of this manuscript. Lastly, I sincerely thank Pat Giuliani for her editing and Nancy Massey for preparing the table.
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Questions or comments about this article may be directed to: Andrea Strayer, MS RN CNRN, Department of Neurological Surgery, University of Wisconsin Hospital and Clinics, K4/844 CSC, 600 Highland Avenue, Madison, WI 53792. She is an adult/geriatric nurse practitioner.
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|Publication:||Journal of Neuroscience Nursing|
|Date:||Apr 1, 2001|
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