An uncommon type of adrenal incidentaloma: a case report of a schwannoma of the adrenal medulla with cytological, histological, and ultrastructural correlation.

Benign nerve sheath tumors of the adrenal gland are an extremely uncommon cause of an incidentaloma. We report a case of a schwannoma of the adrenal medulla in an asymptomatic 51-year-old woman, which was discovered incidentally on a computed tomography scan after routine workup for her degenerative joint diseases of the lumbar spine. Because of the large size and unknown biologic nature of the tumor by clinical and radiographic studies alone, an adrenalectomy was performed. The gross specimen featured a well-circumscribed medullary based tumor with cystic degeneration. The diagnosis of a nerve sheath tumor was based on classic histological findings, supported by S-100 positivity, and ultrastructurally by the finding of typical Schwann cells. The cytological diagnosis from the fine-needle aspiration biopsy material obtained at the time of gross examination was much more challenging on retrospective review. The aspirated material showed a round- to oval-cell predominant smear with occasional striking anisonucleosis, intranuclear inclusions (so-called ancient change), and pigment deposition. A review of the histogenesis and differential diagnosis of this common nerve sheath tumor in this unusual location is discussed.