Acellular pale fluid is seen within irregular dilated lymphatic channel. Note the presence of valves, a helpful clue to identification.
Bland endothelial cells line the ectatic lymphovascular spaces.
Lymphangiomas of the skin can be broadly divided into superficial or deep types. The superficial type (lymphangioma circumscriptum) usually appears during infancy and forms small fluid-filled vesicles on the skin, so-called "frog spawn". The deep form (cavernous lymphangioma) is congenital or appears in infancy, usually in the head and neck area.
Note that cystic hygroma is a variant of cavernous lymphangioma most often associated with Turner syndrome and is usually located on the neck or axilla (Busam, Rapini).
Histologically, the superficial form is composed of ectatic lymphovascular spaces with papillary projections (valves); the vascular spaces are centered in the superficial dermis and may extend into the epidermis.
The deep form is located in the dermis or subcutis and similarly, is composed of ectatic lymphovascular spaces. One may see eosinophilic proteinaceous material and scattered RBCs in the lumina. The lining of the these channels are bland endothelial cells. The overlying epidermis may be hyperplastic.
The differential diagnosis includes hemangiomas (numerous RBCs and lack of valves), patch stage of Kaposi sarcoma (cytologic atypia), and angiosarcoma (cytologic atypia). In the latter two entities, the clinical context should also be quite different (Busam).
Complete excision when possible. Application of intralesional OK432 (Picibanil) is a new and effective treatment for macrocystic lesions.
May recur if incompletely excised, but these are benign, with no risk of malignant transformation.
Busam KJ. Dermatopathology: Foundations in Diagnostic Pathology 1st Ed. Philadelphia, PA: Elsevier; 2010: 551-2.
Rapini RP. Practical Dermatopathology. Philadelphia, PA: Elsevier; 2005: 332.