A 4-year-old child presents with an enlarging subcutaneous swelling overlying the midline of the neck. The lesion is excised and the findings are illustrated below. Which of the following diagnoses is CORRECT?
A) Epidermal inclusion cyst
E) Thyroglossal duct cyst
Dermoid cysts are rare and result from aberrant sequestration of ectoderm into the dermis during embryogenesis. They present in children as enlarging subcutaneous swellings along an embryonic fusion plane. Commonly located around the eyes, they may erode into bone. Microscopically, they are lined by a thin stratified squamous epithelium, including a granular layer. They contain abundant loose lamellar orthokeratosis, as well as other normal cutaneous structures such as hair follicles, sebaceous lobules, eccrine glands, apocrine glands, or smooth muscle. The cyst lumen contains fragments of hair shaft.
Epidermoid cysts may occur anywhere on the body at any age. Like dermoid cysts, microscopically they consist of a stratified, squamous epithelium with a granular layer and abundant laminated orthokeratin within the cavity. Unlike dermoid cysts, however, epidermoid cysts lack skin appendages and hair shaft material. They may occasionally rupture inducing a foreign body giant cell reaction.
Branchial cleft cysts are found in the lateral neck along the lymph node chain, on the mandible, or preauricular region. Failure of a portion of the second branchial cleft to involute completely during development results in formation of an epithelium-lined cyst with or without a sinus tract to the overlying skin. This type of cyst may be lined by various types of epithelium (squamous, respiratory, stratified cuboidal). Lymphoid follicles are found within the wall, but true encapsulated lymph node architecture is not identified. They can become tender, inflamed, or develop abscesses, especially during periods of upper respiratory tract infection, due to the lymphoid tissue located beneath the epithelium.
Bronchogenic cysts arise from abnormal ventral budding of the tracheobronchial tree. They are most commonly located on the suprasternal notch, and rarely on the anterior neck and chin. A fistulous tract may attach to the epidermis. They are lined by pseudostratified ciliated columnar epithelium with interspersed goblet cells, and the cyst wall often contains smooth muscle and mucous glands, and, rarely, cartilage.
Bronchogenic cyst. High-power magnification shows cyst lining composed of ciliated pseudostratified epithelium with goblet cells. Focal areas of squamous metaplasia are present.