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Case ReportsAbstract
Atypical cellular neurothekeoma (ACN) is a rare variant of cellular neurothekeoma (CN) that demonstrates cellular atypia, mitotic activity, larger size, and deep infiltration into surrounding tissue. CN classically occurs in young adults on the head and upper extremities and is considered a benign entity, with or without atypical features, with no risk of recurrence or metastasis following complete excision. This case report includes multiple recurrences of ACN arising in the right buttock of a now 81-year-old female with increasing aggressive features over the span of eleven years. In 2013, the patient presented with a 1.0-cm mass on the right buttock. The lesion demonstrated classic features of CN with focal areas of atypical spindle cells and rare mitoses. In 2017, the patient presented with a recurrent mass at the same site measuring 6.5 cm. Morphologically, the mass resembled the original but with more expansive areas of cellular atypia, increased mitotic activity, and infiltration into subcutaneous tissue. Margins were negative. In 2024, the patient presented a third time with a wound of the sacral area. Imaging revealed a 13.5-cm mass with extension through the skeletal muscle down to the level of the sacrum. Histologic examination demonstrated only infiltrative spindle cells with fascicular and plexiform architecture, cytologic pleomorphism, and easily identifiable mitotic figures, compatible with the atypical component of the previously diagnosed ACN. ACN is an uncommon variant of a rare cutaneous neoplasm that despite showing concerning histologic features has, up until now, had no documented cases of aggressive clinical behavior.