Hypercobalaminemia Leading to the Diagnosis of Retroperitoneal Paraganglioma: A Case Report.

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors with heterogeneous clinical presentations, ranging from classic catecholamine-related symptoms to incidental imaging findings. Hypercobalaminemia is most commonly associated with hematologic disorders, liver disease, or solid malignancies, and has been described in association with neuroendocrine tumors; however, a specific association with PPGLs has not been previously reported. We describe the case of a 47-year-old normotensive woman referred for evaluation of persistently elevated serum vitamin B12 levels. Apart from intermittent abdominal discomfort, she was otherwise asymptomatic. After exclusion of common causes of hypercobalaminemia, abdominal imaging revealed a retroperitoneal para-aortic mass. Histopathological and immunohistochemical analyses were consistent with PPGLs, and biochemical testing demonstrated elevated plasma and urinary normetanephrine levels, supporting the diagnosis of a functioning paraganglioma. 68Ga-DOTATOC positron emission tomography (PET) confirmed somatostatin receptor expression without evidence of additional disease, and the patient underwent complete surgical resection. This case illustrates an atypical diagnostic pathway in which isolated hypercobalaminemia prompted further investigation and led to the diagnosis of a retroperitoneal paraganglioma. It reinforces that PPGLs may occur without classic catecholamine-related symptoms and highlights the clinical relevance of unexplained hypercobalaminemia as a laboratory finding warranting further evaluation. Persistent elevation of serum vitamin B12 levels following tumor resection suggests an incidental finding or a possible association with another, as yet unidentified, neoplastic process, emphasizing the importance of continued follow-up.