Pathology of the Head and Neck

266 M. A Luna · K. Pineda-Daboin9Fig. 9.2. Branchial cleft cyst. Wall lined with stratified squamousepitheliumchial cleft cysts constitute approximately 75–80% of allbranchial anomalies, and fistulae and sinuses togetheraccount for 15–20% of all such malformations [1]. Insome series, external fistulae, sinuses and skin tags aremore common than cysts [57].Of all branchial anomalies, 92–99% are associatedwith the second branchial clefts apparatus, probably becauseit is deeper and longer than the others [8]. Use ofthe name “branchial cyst” without further qualificationgenerally refers to a cyst of second branchial origin. Cystsare three times more common than sinuses and fistulaein this apparatus. They typically occur along the anteriorborder of the sternocleidomastoid muscle from the hyoidbone to the suprasternal notch, but have infrequentlybeen described in the midline, just as a thyroglossal ductcyst may occur laterally, as bilateral branchial cleft cysts,or even in the lateral wall of the nasopharynx [8, 85].Branchial cleft anomalies have no gender preference.Most patients (75%) are aged 20–40 years at the time ofdiagnosis. Since fewer than 3% of cysts are found in patientsolder than 50 years, the pathologist must be carefulin making this diagnosis in this age group; a metastaticcystic squamous cell carcinoma in a cervicallymph node may masquerade as a branchial cleft cyst.On pathologic examination the cysts are unilocular,usually between 2 and 6 cm in diameter, and lined withstratified squamous epithelium (90%), respiratory epithelium(8%), or both (2%; Fig. 9.2). Lymphoid aggregateswith or without reactive germinal centres beneaththe lining epithelium are found in the majority of cysts(75–80%). Acute and chronic inflammation, foreignbody giant-cell reaction and fibrosis are the secondarymicroscopic changes in the wall of the cyst. In exceptionalcases, heterotopic salivary tissue may even befound in the wall of the cyst [111]. Carcinoma in situ hasseldom been described in the lining of the cysts [132].Regauer et al. have postulated that the cysts are initiallylined with the endodermally derived pouch type of respiratoryepithelium, which is replaced by squamous epitheliumthrough an intermediate stage of pseudostratifiedtransitional-type epithelium [95].Fistulae and sinuses are more often found at birthor in early childhood than cysts. The external opening,when present, is usually located along the anterior borderof the sternocleidomastoid muscle at the junction ofits middle and lower thirds. The tract, if there is one,follows the carotid sheath; it crosses over the hypoglossalnerve, runs between the internal and external carotidarteries and ends at the tonsillar fossa [122].Thymic cyst and cystic low-grade mucoepidermoidcarcinoma with prominent lymphoid stroma are considerationsin the differential diagnosis. The cyst’s benignlining distinguishes it from metastatic cystic squamouscarcinoma.Complete surgical excision of the cyst, sinus, or fistulais indicated. In a review of 274 patients with branchialremnants treated at the Mayo Clinic, the recurrence ratewas only 2.7% for patients with no history of surgery orinfection, 14% in those with a history of infection and21.2% in those who had undergone prior attempts at surgicalremoval [28].Anomalies from the first branchial arch accountedfor only 8% of all branchial cleft anomalies at the MayoClinic [82]. Of these, 68% were cysts, 16% sinuses and16% fistulae. These anomalies occur predominantly infemales and are found in all age groups. In general, sinusesand fistulae tend to develop in infants and children,whereas cysts are more common in older groups.Clinically, they may masquerade as parotid tumours oras otitis with ear drainage [82].Disorders of the first branchial cleft are classified intotwo types [119]. Type I are those that embryologically duplicatethe membrane (cutaneous) external auditory canal.Accordingly, only ectodermal components are observedunder the microscope. On histologic examinationthey are often confused with epidermoid cysts, for theyare lined solely by keratinised, stratified squamous epithelium,with no adnexal structures or cartilage. Characteristically,they are located medial, inferior or posteriorto the concha and pinna. Drainage from cysts or fistulaemay occur in any of these sites. The fistula tract or sinusmay parallel the external auditory canal and ends in ablind cul de sac at the level of the mesotympanum.Type II deformities are composed of both ectodermaland mesodermal elements and therefore contain,in addition to skin, cutaneous appendages and cartilage(Fig. 9.3). Patients with this defect usually present withan abscess or fistula at a point just below the angle of themandible, through the parotid gland, toward the externalauditory canal. Type II defects are therefore more intimatelyassociated with the parotid gland than are type Idefects. Sometimes an anomaly cannot be distinguishedas type I or type II. In those instances, Olsen et al. suggestedthat the abnormality be classified only as to whetherit is a cyst, sinus, or fistula [82]. Complete excision is