Magnetic resonance imaging in the diagnosis of subglottic cysts of infancy: case report and review. (Original Article).

Abstract

Subglottic cysts can cause stridor and respiratory distress in the infant. The diagnosis of subglottic cysts is often confirmed during direct laryngoscopy and bronchoscopy. We describe the case of a 6-month-old boy with bilateral subglottic cysts that were preoperatively diagnosed by magnetic resonance imaging (MRI). We also review the current literature on the diagnosis and treatment of subglottic cysts. Up until now, 63 cases of subglottic cysts were reported in the literature since 1966, and most were diagnosed by direct endoscopy. In this article, we describe a new case and we provide the first published report of the novel use of MRI in diagnosing this lesion.

Introduction

Advances in neonatology have led to an increase in survival among extremely premature infants. As a result, a growing number of children have a medical history significant for early intubation. Neonatal intubation is associated with the development of ductal cysts in the subglottic region.

Up until now, 63 cases of infantile subglottic cysts have been reported in the literature since 1966. (1-13) However, little was written in these articles about the preoperative evaluation of these patients other than the history, physical examination findings, and use of endoscopy. In this article, we present the first report of the use of contrastenhanced magnetic resonance imaging (MRI) in the preoperative diagnosis of subglottic cysts. Our use of MRI allowed for more effective preoperative counseling of the parents and enhanced our ability to choose an appropriate surgical procedure. We also review the relevant literature relating to subglottic cysts and their radiologic diagnosis.

Case report

A white boy born at 37 weeks' gestation had been intubated for 2 days during the neonatal period. When he was 2 months of age, he was taken to a pediatric pulmonologist for evaluation of stridor. He was treated with a course of steroids, and he showed improvement. When he reached 6 months of age, his symptoms slowly returned and he was again taken for medical care. Flexible bronchoscopy revealed the presence of bilateral subglottic masses in the posterolateral aspect of the subglottis. The family was resistant to any operative intervention, including tracheostomy to stabilize the child's airway before further management could be undertaken.

Reluctant to proceed with any surgery, the family sought consultation for less invasive management at the pediatric otolaryngology service of our institution. After examining the child, we obtained an MRI with gadolinium contrast to further evaluate the substance of the subglottic space and to assist in further counseling of the family regarding surgical management. MRI revealed the presence of two subglottic masses whose radiologic appearance was consistent with that of a cyst (figure 1).

The family was then counseled that tracheostomy would be performed only if rigid bronchoscopy revealed that a more conservative treatment would endanger the child. Direct laryngoscopy and bronchoscopy confirmed the presence of bilateral subglottic cysts (figure 2).

The cysts were successfully marsupialized with a pediatric Healy subglottiscope and a [CO.sub.2] laser (figure 3). Repeat bronchoscopy 2 months later showed that the airway was normal in caliber and appearance. The child remained asymptomatic at the 1-year follow-up.

Review of published cases

We conducted a Medline search to identify all case reports and other relevant articles on sub-glottic cysts in infants that have been published since 1966. Including ours, 64 cases were available for review (table). Whenever the information was noted in the original article, we recorded the number of days of intubation, the number of months postintubation until the patient was subsequently evaluated for cysts, the type of treatment, and the number of recurrences.

The number of days of intubation ranged from 1 to 90 (mean: 26.2). The number of months to postintubation cyst evaluation ranged from 1.5 to 25 (mean: 8). The vast majority of patients were diagnosed by direct laryngoscopy without the use of adjuvant imaging. Two reports mentioned the use of soft-tissue lateral neck x-rays to assist in the work-up. (1,12) No article reported the use of computed tomography (CT) or MRI to assist in the diagnosis.

Most subglottic cysts were managed endoscopically by direct rupture, laser excision, marsupialization, or removal with cupped forceps. Six of these patients (9.4%) underwent staged endoscopic procedures. (8,9) Thirteen patients (20.3%) required tracheostomy, (7,8,10,11,13) three patients (4.7%) underwent an anterior cricoid split, (7) and three others were treated with laryngotracheal reconstruction. (7,8) Six patients (9.4%) died; in three of them, the subglottic cysts were discovered for the first time at autopsy. (1,2,7,8,10) There were 11 reported recurrences (17.2%). (4,7,8,11,13)

Discussion

The incidence of subglottic cysts appears to be increasing. Our review of the English-language literature published from 1966 through 1989 found only 23 reported cases. Since 1990, the number of reported cases, including ours, is 41. This increase in the number of patients diagnosed with subglottic cysts is thought to be related to improvements in survival of very premature infants. Although the pathogenesis of subglottic cysts is not completely understood, it appears to be strongly associated with early intubation.

Intubation can lead to damage of the laryngeal, subglottic, and tracheal mucosa within only a few days. In a study of postmortem infants, Hawkins found that after as few as 6 days of intubation, 93% of examined airways showed signs of subglottic ulceration, squamous metaplasia, and resultant subepithelial fibrosis. (14) It is believed that this mucosal damage leads to scarring and eventual occlusion of the ducts of the submucosal glands. The occluded glands continue to produce mucus, which leads to the formation of retention cysts.

Even only 1 or 2 days of intubation can be sufficient to lead to the development of subglottic cysts. Smith et al," Toriumi et al, (7) and Tierney et al (13) reported that subglottic cysts had developed in children who had been intubated for only 1, 2, and 3 days, respectively. Moreover, in their report of 11 patients with subglottic cysts, Smith et al found no relationship between the duration of intubation and the severity of the cysts. (11)

As is the case in most infants with airway distress, an accurate diagnosis is drawn from the history, physical examination, and an appropriate level of suspicion. A diagnosis of subglottic cysts should be considered in all patients who have a history of intubation, regardless of its duration. The definitive diagnosis is made during direct laryngoscopy and bronchoscopy. Children with suspected pathology below the level of the true vocal folds should undergo endoscopy because it is considered to be part of the complete physical examination of the airway.

Our review of the literature provided little information about the role that imaging might play in the preoperative assessment of these patients. Reed and Myer published one of the few articles that discussed the use of radiography to assist in the diagnosis of subglottic cysts prior to endoscopy. (12) They discussed plain soft-tissue radiographs of the neck, but made no comment on the role of CT or MRI.

On MRI, subglottic cysts have distinct characteristics that help differentiate them from other subglottic pathology. MRI appears to be superior to CT in the evaluation of cystic and soft-tissue pathology of the larynx because of its multiplanar capability, contrast resolution, and ability to demonstrate the full extent of the mass and its relationship to vascular and soft-tissue structures in all compartments of the neck. On T2-weighted images, the signal intensity is high (figure 1, A). On T1-weighted images, the fluid content of the subglottic cysts has a low signal intensity, similar to that of water. Following the administration of gadolinium to our patient, there was no enhancement of the cysts (figure 1, B).

The characteristic appearance and location of subglottic cysts on MRI helps to distinguish them from thyroglossal duct cysts, branchial cleft cysts, cystic hygromas, dermoid cysts, and other neck pathologies. Hemangiomas can mimic subglottic cysts, but on MRI they appear as soft-tissue masses and are characterized by intermediate signal intensity (related to muscle) on T1-weighted imaging and by high signal intensity on T2-weighted imaging. Also, MRI can demonstrate multiple areas of signal void in the hemangiomas, which represent vessels. After the administration of gadolinium contrast, these masses enhance homogenously. Soft-tissue stenosis of the subglottic region appears as areas of narrowing, without associated mass effect or abnormal enhancement.

The importance of radiologic preoperative assessment cannot be overstated. Most subglottic cysts can be treated endoscopically without the need for open tracheal reconstruction or tracheostomy. Two of the three patients in our review who underwent laryngotracheal reconstruction had been diagnosed with soft-tissue subglottic stenosis. (8) In both cases, the cysts were discovered during the reconstruction. The authors made no mention of the role that imaging might have played in helping differentiate subgiottic stenoses from subglottic cysts. Unlike subglottic cysts, soft-tissue stenoses more often require temporary tracheostomy and subsequent tracheal reconstruction. The distinct imaging characteristics of soft-tissue stenoses and subglottic cysts on MRI aid in their differentiation. Again, the use of MRI can help determine which type of procedure should be performed and whether a tracheostomy will be necessary.

The character of subglottic cysts can usually be appreciated on direct endoscopy. These cysts can appear singly or multiply in a variety of locations in the subglottis. Nevertheless, it is important to remember that subglottic cysts are not always obvious during endoscopy, and those that occur deeper in the submucosal tissues can be missed. To date, four cases of subglottic cysts that were not initially recognized on initial endoscopy have been reported. (7,8,13) Each of these patients underwent tracheostomy for what was believed to be a soft-tissue subglottic stenosis. The cysts were later recognized during laryngotracheal reconstruction (2 patients), on direct micro-laryngobronchoscopy (1 patient), and at autopsy (1 patient). The realization that subglottic cysts can be missed during endoscopy adds support to the use of MRI in selected cases as an adjunct to preoperative evaluation.

With regard to the treatment options at the time of endoscopy--direct rupture, laser ablation, marsupialization, removal by cupped forceps, and occasionally tracheostomy--our review did not find that one was superior to any other, nor did we find an association between the particular type of surgical procedure and the incidence of recurrence. Likewise, the use of staged endoscopic procedures also had no affect on the recurrence rate. We advocate that follow-up endoscopy be performed to rule out recurrence and to evaluate the patency of the patient's airway.

In conclusion, our investigation should not be interpreted as an endorsement for replacing pediatric bronchoscopy with MRI. However, our work does indicate that the use of MRI in selected patients can confirm the diagnosis of subglottic cysts preoperatively and help differentiate them from other subglottic pathology. This should allow for a more informed parental counseling and a more directed formulation of a surgical plan. The clinician is encouraged to consider MRI whenever there is a reluctance to proceed to the operating room or whenever the etiology of subglottic pathology is not certain.

Table

Summary of the 64 cases of subglottic cysts reported since 1966

                                          Days     Months to
Author                        No. pts.  intubated  evaluation

Wigger and Tang, 1968 (1)        1         36          ?
Chamberlain, 1970 (2)            1          ?          ?
DeSanto et al, 1970 (3)          1          ?          ?
Couriel and Phelan, 1981 (4)     3       8 to 49   3.5 to 24
Fan, 1984 (5)                    1          ?          14
Mitchell et al, 1987 (6)         4          ?        2 to 6
Toriumi et al, 1987 (7)          12      2 to 60    2 to 11


Smith et al, 1990 (8)            9       5 to 90   1.5 to 18

Triglia et al, 1991 (9)          1         15          ?
Downing et al, 1993 (10)         13      7 to 53    3 to 15
Smith et al, 1994 (11)           11      1 to 24    3 to 25
Reed and Myer, 1995 (12)         1         75         5.5
Tierney et al, 1997 (13)         5       3 to 14    9 to 18
Mobley et al, 2002 (+)           1          2          2

                                  Open
Author                         procedures (*)  Recurrences

Wigger and Tang, 1968 (1)
Chamberlain, 1970 (2)
DeSanto et al, 1970 (3)
Couriel and Phelan, 1981 (4)                        1
Fan, 1984 (5)
Mitchell et al, 1987 (6)
Toriumi et al, 1987 (7)       ACS (n = 3),          4
                              LTR (n = 1),
                              Trach (n = 3)
Smith et al, 1990 (8)         LTR (n = 2),          1
                              Trach (n = 3)
Triglia et al, 1991 (9)
Downing et al, 1993 (10)      Trach (n = 3)
Smith et al, 1994 (11)        Trach (n = 3)         2
Reed and Myer, 1995 (12)
Tierney et al, 1997 (13)      Trach (n = 1)         3
Mobley et al, 2002 (+)

(*)ACS = anterior cricoid split; LTR = laryngotrachel reconstruction;
Trach = tracheostomy.

(+)Present case.

References

(1.) Wigger HJ, Tang P. Fatal laryngeal obstruction by iatrogenic subglottic cyst. J Pediatr 1968;72:815-20.

(2.) Chamberlain D. Congenital subglottic cyst of the larynx. A case report. Laryngoscope 1970;80:254-93

(3.) DeSanto LW, Devine KD, Weiland LH. Cysts of the larynx--classification. Laryngoscope 1970:80:145-76.

(4.) Couriel JM, Phelan PD. Subglottic cysts: A complication of neonatal endotracheal intubation? Pediatrics 198l;68:103-5.

(5.) Fan LL. Transnasal fiberoptic endoscopy in children with obstructive apnea. Crit Care Med 1984:12:590-2.

(6.) Mitchell DB, Irwin BC, Bailey CM, Evans JN. Cysts of the infant larynx. J Laryngol Otol 1987;l0l:833-7.

(7.) Toriumi DM, Miller DR, Holinger LD. Acquired subglottic cysts in premature infants. Int J Pediatr Otorhinolaryngol 1987;14:151-60.

(8.) Smith JD, Cotton R, [Myer] CM III. Subglottic cysts in the premature infant. Arch Otolaryngol Head Neck Surg 1990:116:479-82.

(9.) Triglia JM, Portaspana T, Cannoni M, Pech A. Subglottic cyst in a newborn. J Laryngol Otol 1991;105:222-3.

(10.) Downing GJ, Hayen LK, Kilbride HW. Acquired subglottic cysts in the low-birth-weight infant. Characteristics, treatment, and outcome. Am J Dis Child 1993;147:971-4.

(11.) Smith SP, Berkowitz RG, Phelan PD. Acquired subglottic cysts in infancy. Arch Otolaryngol Head Neck Surg 1994;120:921-4.

(12.) Reed JM, Myer CM III. Radiographic evaluation of a subglottic cyst in an infant. Am J Otolaryngol 1995;16:329-30.

(13.) Tierney PA, Francis I, Morrison GA. Acquired subglottic cysts in the low birth weight, pre-term infant, J Laryngol Otol 1997; 111:478-81.

(14.) Hawkins DB. Hyaline membrane disease of the neonate, prolonged intubation in management: Effects on the larynx. Laryngoscope 1978;88:201-2.

From the Department of Otolaryngology, College of Medicine, University of Illinois at Chicago (Dr. Mobley), the Department of Radiology, Miami Children's Hospital (Dr. Pacheco), and the Department of Pediatric Otolaryngology-Head and Neck Surgery, Nemours Children's Clinic, Jacksonville, Fla. (Dr. Josephson).

Reprint requests: Gary D. Josephson, MD, Associate Chief, Pediatric Otolaryngology-Head and Neck Surgery, Nemours Children's Clinic, 807 Nira St., Jacksonville, FL 32207. Phone: [phone]; fax: [phone]; e-mail: [e-mail]

Originally presented as a poster during the annual meeting of the American Academy of Otolaryngology-Head and Neck Surgery; New Orleans; Sept. 27, 1999.