Fine-needle aspiration cytology of metastatic squamous-cell carcinoma arising in a pilonidal sinus, with literature review.

Fewer than 50 cases of carcinoma arising in a pilonidal sinus have been reported, with only 5 patients having documented inguinal lymph node metastases. This is the first report of the fine-needle aspiration (FNA) diagnosis of this uncommon clinical situation of squamous-cell carcinoma arising in a pilonidal sinus, metastatic to an inguinal lymph node. We report on a 59-yr-old male with squamous-cell carcinoma arising in a pilonidal sinus who presented with inguinal adenopathy. FNA biopsy of a lymph node was performed, resulting in a diagnosis of metastatic squamous-cell carcinoma. FNA biopsy is useful in the evaluation of patients with inguinal adenopathy and a history of malignancy arising in a pilonidal sinus. The possibility of this rare complication should also be considered when metastatic squamous-cell carcinoma to an inguinal lymph node is diagnosed by FNA cytology in patients having an unknown primary except for a change in a long-standing pilonidal cyst.