SAT-481 - When the Adrenal Gland Is the Clue: Extramedullary Adrenal Plasmacytoma Masquerading as an Adrenal Incidentaloma

Adrenal masses are commonly encountered in endocrine practice and although with both imaging and biochemical workup mostly are benign adenomas or hormonically active tumors, there are rare instances where infiltrative malignancies may mimic typical adrenal pathology. Extramedullary plasmacytoma is a plasma cell neoplasm arising outside the bone marrow, usually in the upper aerodigestive tract, with adrenal involvement being exceedingly rare. For endocrinologists, recognizing non-endocrine causes of adrenal masses is critical, as misclassification may lead to unsafe biopsy, delayed diagnosis, or inappropriate surgical intervention. Systematic hormonal evaluation—particularly exclusion of pheochromocytoma, cortisol or aldosterone secreting adenomas, or adrenocortical carcinomas—remains a cornerstone of safe adrenal mass management.

We present a 67-year-old male with a history of Chronic Obstructive Pulmonary Disease, Type 2 Diabetes Mellitus and former smoker who presented with chest pain and dyspnea. A computed tomography angiography of the chest was performed to rule out pulmonary embolism which revealed a retroperitoneal soft tissue mass adjacent to the left adrenal gland and lytic lesions of the sternum. Subsequent non-contrast abdomen & pelvis CT demonstrated a rapidly enlarging left adrenal mass measuring 4.1 × 4.1 cm with an attenuation of 44 Hounsfield units. Notably, a low-dose chest CT scan performed four months earlier showed no adrenal lesion.

Given rapid growth, high attenuation, and concomitant lytic bone lesions, endocrinology and hematology-oncology were consulted. Comprehensive endocrine evaluation excluded functional adrenal disease, with normal plasma metanephrines, aldosterone–renin ratio, and cortisol testing. Concurrent hematologic evaluation revealed elevated serum free kappa light chains, kappa/lambda ratio of 4.22, and M-spike of 3.0 g/dL on protein electrophoresis. Bone marrow biopsy demonstrated high-risk multiple myeloma with 12% clonal plasma cells. Following biochemical exclusion of pheochromocytoma, adrenal biopsy was safely performed and confirmed extramedullary plasmacytoma with cytology showing sheets of atypical plasmacytoid cells, and tumor cells positive for CD38 and MUM1. After careful multidisciplinary evaluation, the patient initiated systemic chemotherapy.

This case illustrates a rare but clinically significant cause of an adrenal mass in endocrine practice. In patients with known or newly diagnosed malignancy, adrenal lesions should not be presumed incidental. Endocrinologists play a pivotal role in identifying imaging red flags, ensuring complete hormonal exclusion prior to biopsy, and guiding multidisciplinary decision-making. Extramedullary adrenal plasmacytoma represents a rare diagnostic pitfall that underscores the endocrinologist’s role as gatekeeper in adrenal mass evaluation.

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