An uncommon case of pheochromocytoma with positive biochemical workup and absence of tumor.

Summary: Pheochromocytomas are rare neuroendocrine tumors derived from adrenal chromaffin cells that result in hyperactivity of the sympathetic nervous system. We present the case of a patient with biochemical evidence of pheochromocytoma, but surgical pathology revealed absence of tumor. This is an 80-year-old female with a past medical history of metastatic follicular lymphoma and hypertension with an incidental 1.4 cm right-sided adrenal nodule noted on a PET-CT scan. Her hypertension was treated with three different antihypertensive agents. Subsequent imaging with non-contrast CT of abdomen and pelvis showed a right adrenal incidentaloma with 16 Hounsfield units. Abdominal MRI with and without contrast revealed atypical signal loss on the out-of-phase imaging. Plasma normetanephrines were approximately 2.4 times higher than the upper limit of normal. Her urinary normetanephrines were higher than the upper limit of normal, suggestive of pheochromocytoma. The patient proceeded with robotically assisted laparoscopic right adrenalectomy and postoperatively required vasopressors. Surgical pathology showed adrenal cortical hyperplasia and medullary infarction associated with fibrosis. However, the noted phases of necrosis with predominant fibrosis match the time interval between clinical diagnosis and surgical management. Postoperative metanephrines normalized 4 weeks after surgery, indicating successful surgical resection of autonomous secretion of metanephrines. This is the only known case of biochemical evidence of pheochromocytoma with no histologic evidence of tumor.

Learning points: Biochemical evidence, clinical presentation and imaging studies of pheochromocytoma are crucial for its diagnosis. Due to the vascular nature of pheochromocytoma, there is a potential for the tumor to infarct. Plasma normetanephrines of greater than twice the upper limit of normal have high specificity for pheochromocytoma.