PAT-7. Squamous epithelium-lined cystic lesion with cytologic atypia in benign inguinal lymph node.

Epithelial inclusions in lymph nodes are rare. Squamous inclusions in lymph nodes are problematic. In some instances distinction between a benign inclusion and metastatic well-differentiated squamous cell carcinoma cannot be resolved. A 56-year-old male with a long history of smoking and a prior history of sarcoidosis presented for evaluation of a left inguinal mass. The initial clinical diagnosis was inguinal hernia. A CT scan showed a mass lesion that was interpreted as a possible lymph node. The mass was excised and sent for surgical pathology examination. The excisional biopsy consisted of a 5 X 3.5 X 3.5 cm. encapsulated tan-white round soft mass filled with tan-white, soft, grumous material. Microscopic sections showed an intranodal cystic lesion lined by squamous epithelium, which had a prominent granular layer and abundant keratin formation. In some areas the epithelium was attenuated with significant enlarged, hyperchromatic nuclei and a somewhat disorganized pattern of growth. Mitotic figures were seen in all levels of the epithelium. Focally, the squamous epithelium was more thickened with an invasive pattern of growth including some islands of squamous epithelium non-contiguous with the squamous cyst. Pigmentation was seen, with numerous pigmented dendritic melanocytes within the squamous epithelium. A microscopic cystic lesion lined by well-differentiated squamous epithelium in the lymph node can be a diagnostic problem. The presence of cytologic atypia, mitotic figures, and an infiltrative growth pattern makes it difficult to exclude a well-differentiated metastatic squamous cell carcinoma. Cases of squamous inclusion cysts with this appearance in the lymph nodes have been reported in the axilla, peripancreatic region and para-aortic nodes. To our knowledge, this is the first case that is found in the inguinal lymph node.

S.S. Lim, MD, K. Hewan-Lowe, MD, and L.J. Dobbs, MD, PhD. Pitt County Memorial Hospital/Brody School of Medicine, East Carolina University, Greenville, NC.