Peritheliomatous pattern: A diagnostic clue for diagnosing metastatic melanoma in cytology

A peritheliomatous pattern (PP) in tumors is characterized by a sheath of viable tumor cells closely surrounding a central blood vessel. In the authors' cytology practice, such a PP has been recognized in several metastatic melanoma specimens. The aim of this study was to evaluate the frequency of a PP in cytology samples of melanoma in comparison with other tumors.

Eighty archival fine-needle aspiration (FNA) cases of metastatic melanoma were compared with 65 control cases (35 poorly differentiated/metastatic carcinomas, 15 lymphomas, and 15 recurrent/metastatic/high-grade sarcomas). Cytologic findings were correlated with corresponding histologic specimens, which were available for 44 cases (55%) in the melanoma group and for 23 cases (35.38%) in the control group. All slides were examined for a PP and were semiquantitatively graded for comparison.

A PP was present in 51.3% of the cytologic preparations (n = 41) among the melanoma group cases, whereas in the control group, a PP was present in only 3.1% of the cases (n = 2). A PP was present in 65.9% of melanomas with available histologic sections (n = 29) and in 8.7% of tissue samples from the control group (n = 2). A PP was seen more often in cell blocks than direct smear preparations (51.3% vs 40.0%) from patients with melanoma.

The presence of a characteristic PP can be helpful in diagnosing melanoma in FNA samples because it was present in almost half of the metastatic melanoma cases in this study and was rarely present in other tumor types. A PP is easier to recognize and more often presents in cell blocks than aspirate smears. Ancillary studies such as immunohistochemistry are helpful for excluding other entities that may exhibit a PP.