LATERAL NECK CYSTS - THE BRANCHIAL THEORY REVISITED - A CRITICAL-REVIEW AND CLINICOPATHOLOGICAL STUDY OF 97 CASES WITH SPECIAL EMPHASIS ON CYTOKERATIN EXPRESSION

Theories regarding the origin of lateral neck cysts (LNC) range from c ongenital branchial pouch abnormalities to acquired salivary gland inc lusions within lymph nodes. We analyzed 97 LNC histologically and eval uated their cytokeratin (CK) profile in a search for their derivation. 77/97 LNC were located in soft tissues, 20/97 within lymph nodes. LNC of young patients and of recent symptomatic presentation in older pat ients were lined by respiratory epithelium with scant lymphoid tissue, with expression of ''simple epithelial'' CK in ciliated cells and bim odal expression of ''simple'' and ''stratified-epithelial-type'' CK in basal cells. In longer standing symptomatic LNC, respiratory epitheli um alternated with transitional-type pseudostratified epithelium with intraepithelial Langerhans cells and lymphoid hyperplasia, or consiste d exclusively of squamous epithelium. We propose that respiratory epit helium is the ''native'' epithelium of LNC and squamous metaplasia res ults from inflammation induced stem cell hyperplasia in respiratory ep ithelium, evidenced by co-expression of ''simple'' and ''stratified-ep ithelial-type'' CK in all cells of transitional-type pseudostratified epithelium? the early stage in metaplastic transformation. Respiratory epithelium predominates in early LNC, lines pharyngeal tonsils and th e recessus tonsillo-tubalis, and is a minor constituent of palatine to nsil but is not present in salivary glands. None of the LNC contained dysplasia, atypia, or carcinoma, or were associated with a primary car cinoma of tonsils or head and neck. We demonstrate that LNC arise from developmental remnants (congenital) of the 2nd branchial pouch, which may lie dormant for many years. Symptomatic enlargement, squamous met aplasia and lymphoid hyperplasia ensue as a consequence of immunologic stimulation, a development reflected in hyperplastic palatine tonsils .