Sustentaculoma of the Adrenal Medulla in a Young Japanese Male Patient Observed for an Extended Period After Surgery

This report describes an exceptionally rare case of sustentaculoma, a morphologically distinctive neoplasm of the left adrenal medulla, in a 39-year-old Japanese male. No hormones showed abnormal elevation. There were no signs of hyperglycemia or hypertension, and his medical and family history showed no significant findings. Abdominal computed tomography (CT) and magnetic resonance imaging (MRI) revealed a well-defined, smoothly bordered left adrenal tumor measuring 3.3 × 2.3 cm. Macroscopically, the neoplasm presented as a well-defined solid mass measuring 3.5 × 2.7 × 2.5 cm, exhibiting a grayish-white coloration. Histologically, it was encapsulated by a thin fibrous capsule. The neoplasm comprised irregularly sized solid nests and collagenous fibrosis in the stroma; the neoplastic cells featured round nuclei and eosinophilic cytoplasm with indistinct cellular boundaries. Immunohistochemical staining revealed positivity for vimentin, S-100 protein, CD56 (NCAM), CD45 (LCA), and CD68 (KP-1). Electron microscopy showed numerous spherical mitochondria within the cytoplasm, interspersed with pseudomesaxons among the cells. The patient has been closely monitored in the urology outpatient department, and as of 16 years post-surgery, no recurrence or metastasis has been observed. This case is particularly rare; to our knowledge, it represents the second reported instance globally.