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

## TL;DR

A rare case of retroperitoneal paraganglioma was diagnosed through unexplained high vitamin B12 levels, showing the importance of investigating unusual lab results.

## Contribution

This is the first reported case linking hypercobalaminemia specifically to paragangliomas.

## Key findings

- A retroperitoneal paraganglioma was diagnosed in a patient with persistent hypercobalaminemia.
- The tumor was functioning, as evidenced by elevated normetanephrine levels.
- Hypercobalaminemia persisted after surgery, suggesting an unknown underlying process.

## Abstract

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.