Received March 20, 2004; Revised May 12, 2004; Accepted May 13, 2004. Author to whom all correspondence and reprint requests should be addressed: Professor Dr. Vera Popovic, Institute of Endocrinology, Dr Subotica 13, 11000 Belgrade, Serbia. E-mail: popver@eunet.yu Retroperitoneal Malignant Fibrous Histiocytoma Mimicking Pheochromocytoma Sandra Pekic, 1 Svetozar Damjanovic, 1 Marina Djurovic, 1 Mirjana Doknic, 1 Milan Petakov, 1 Dragana Miljic, 1 Zorka Milovanovic, 2 Kalman Kovacs, 3 and Vera Popovic 1 1 Neuroendocrine Unit, Institute of Endocrinology, University Clinical Center, 2 National Institute of Radiology and Oncology, Belgrade, Serbia and 3 Department of Pathology, St Michael’s Hospital, University of Toronto, Toronto, Canada Endocrine, vol. 24, no. 1, 99–103, June 2004 0969–711X/04/24:99–103/$25.00 © 2004 by Humana Press Inc. All rights of any nature whatsoever reserved. 99 uptake adjacent to the adrenal has been reported in patients with obstructive hydronephrosis, dilated renal pelvis, renal failure, and unilateral renal artery stenosis (3,4). Malignant fibrous histiocytomas (MFH) are rare tumors, frequently associated with leukemoid reaction, attributed to tumor production of unidentified hematopoietic factors (5,6). We present the case of a 52-yr-old man with a large retro- peritoneal mass assumed to be a malignant dopamine-secret- ing adrenal tumor based on positive MIBG and elevated uri- nary dopamine levels. The mass was surgically resected and histology revealed malignant fibrous histiocytoma. Case Report A 52-yr-old man was admitted into our Institution with a large retroperitoneal mass thought to be an adrenal tumor. Initially he presented with abdominal pain, hypertension (up to 190/120 mmHg) with postural hypotension (100/70 mmHg), palpitations with tachycardia (up to 160/min), profuse sweating, pallor, nervousness and anxiety, inter- mittent fever (38–39°C), and severe weight loss (20 kg in 6 months). Laboratory findings where compatible with “inflamma- tory syndrome”: WBC 72.500  10 9 with granulocytosis (78% of neutrophils), high sedimentation rate, and elevated leukocytic alkaline phosphatase (APL; Table 1). Serum cortisol, T4, TSH, calcitonin, PRA, aldosterone, urinary nor- adrenaline, and adrenaline levels were within normal range (Table 1). Urinary dopamine concentrations were elevated two- to threefold (518–1005 µg/24 h, normal up to 300 µg/ 24 h). Serum NSE was elevated twofold. Ultrasonography and computed tomography (CT) scan of the abdomen dem- onstrated a 10  7.5 cm mass in the region of left adrenal (Fig. 1). After 1 mo, scintigraphy with 768 µCi [ 131 I]MIBG showed uptake in the region of left adrenal (Fig. 2). After pretreatment with phenoxybenzamine (4  10 mg) and meto- prolol (50 mg/d) for 2 wk the patient underwent surgery. Intraoperative findings confirmed hydronephrosis of the left kidney and compressed renal vessels due to compres- sion by the large retroperitoneal mass. Postoperative evalu- ation was not possible due to rapid clinical deterioration. Autopsy was not performed. We report the case of a 52-yr-old man with a mass in the area of the left adrenal. The clinical features, MIBG uptake, and elevated urinary dopamine levels sug- gested the diagnosis of pheochromocytoma. He pre- sented with unstable hypertension, tachycardia, weight loss, and the “inflammatory syndrome” (fever, leuko- cytosis, and high sedimentation rate). Clinical find- ings, preoperative radiographic (sonography, CT scan, [ 131 I]MIBG scintigraphy), and endocrine evaluations (elevated 24-h urinary dopamine) were suggestive of a dopamine-secreting adrenal tumor. The mass was resected and on histologic examination showed the characteristic features of a malignant fibrous histio- cytoma (MFH). The tumor cells were immunopositive for neuron-specific enolase (NSE), vimentin, CD-68, S-100, desmin, and immunonegative for chromogra- nin A, synaptophysin, neurofilament protein, and low- molecular-weight keratin, indicating that this tumor was not able to synthesize catecholamines. The pro- longed retention of the tracer (MIBG) was interpreted as a consequence of obstructive hydronephrosis, while elevated urinary dopamine levels were assumed to be due to compression of the renal vessels by the large retroperitoneal mass. Key Words: Malignant fibrous histiocytoma; [ 131 I]MIBG scintigraphy; dopamine pathology; retroperitoneal neo- plasm. Introduction Radiolabeled 131 I-metaoiodobenzylguanidine ([ 131 I]MIBG) scintigraphy is known for its high specificity (98.9%) in detecting pheochromocytoma and other tumors of neural crest origin (1). A misleading positive MIBG scan is very rare. There are data on adrenal adenomas and carcinomas with misleading positive MIBG scans (2). Focal [ 131 I]MIBG