Recurrent malignant pheochromocytoma with unusual omental metastasis: ⁶⁸Ga-DOTANOC PET/CT and ¹³¹I-MIBG SPECT/CT scintigraphy findings

A 49-year-old male who had undergone right adrenalectomy for pheochromocytoma 8-years ago presented with impaired glucose tolerance with diabetes and hypertension since 1 year. His 24 h urine vanilylmandelic acid was elevated in range of 233 mg/24 h (normal: 0-13.6 mg/24 h). His computed tomography (CT) abdomen revealed multiple intra-abdominal masses in right suprarenal, perirenal, retrocaval, peripancreatic, and in omentum with vivid arterial enhancement. The patient was referred for ⁶⁸Ga-labeled [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-NaI3-octreotide (DOTANOC) positron emission tomography (PET)/CT study for restaging purpose. ⁶⁸Ga-DOTANOC PET/CT revealed large aortocaval lymph nodal mass (6.4 × 5.3 cm) with area of necrosis and DOTANOC uptake in non-necrotic part (SUV max-3.1). Multiple peripancreatic, mesenteric, and retroperitoneal lymph nodes were noted with increased tracer uptake. It also showed multiple omental deposit with increased tracer uptake (SUVmax-2.5) [Figure 1]. ¹³¹I-metaiodobenzylguanidine (MIBG) planer whole body scintigraphy was performed to evaluate the therapeutic potential of ¹³¹I-MIBG in view of the metastatic nature and inoperability of the disease. ¹³¹I-MIBG study showed increased tracer uptake in upper and mid abdomen regions. Single-photon emission computed tomography (SPECT)/CT study revealed MIBG concentrating lesions involving aortocaval, multiple peripancreatic, mesenteric and retroperitoneal lymph node, and omental deposits suggestive of recurrent disease [Figure 2]. Ultrasound-guided aspirate from right suprarenal lesion and omental lesion showed cytomorphological feature compatible with pheochromocytoma [Figure 3]. As the lesions were showing more ¹³¹I-MIBG uptake than ⁶⁸Ga-DOTANOC uptake, the patient was taken for ¹³¹I-MIBG therapy.

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Figure 1 ⁶⁸Ga-DOTANOC PET/CT revealing large aortocaval lymph nodal mass (6.4 × 5.3 cm) with area of necrosis and DOTANOC uptake in non-necrotic part (a-c, arrows). It also showed an omental deposit with increased tracer uptake (a, d, e, dotted arrows). ⁶⁸Ga-DOTANOC = ⁶⁸Ga-labeled [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-NaI3-octreotide, PET = Positron emission tomography, CT = Computed tomography

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Figure 2 ¹³¹I-MIBG planer whole body scintigraphy anterior (a) and posterior (b) images showing increased tracer uptake in upper and mid abdomen regions. SPECT/CT study revealed MIBG concentrating lesions involving aortocaval lymph node (c and d, arrows) and a omental deposit suggestive of recurrent disease (e and f, dotted arrows). ¹³¹I-MIBG = ¹³¹I-metaiodobenzylguanidine, SPECT = Single-photon emission computed tomography, CT = Computed tomography

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Figure 3 Ultrasound-guided aspirate from right suprarenal lesion and omental lesion (a) (×10), (b) (×20), (c) (×40) shows groups of cell in nesting pattern with abundant eosinophilic cytoplasm and rounded nuclei showing mild nuclear pleomorphism compatible with pheochromocytoma

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Pheochromocytomas are rare catecholamine-secreting tumors derived from chromaffin cells. In all, 10-50% of intra-abdominal extra-adrenal paraganglioma are malignant.[1] Metastatic spread is the only reliable criterion for the diagnosis of malignant pheochromocytoma. In 7% of the cases, metastasis occurred in more than one organ.[23] The most common sites of metastasis are lungs, liver, lymph nodes, and bones. Previous studies with ¹¹¹In-Octreotide have shown higher sensitivity for detecting metastatic pheochromocytoma than for detecting benign pheochromocytoma.[4] ⁶⁸Ga-DOTANOC PET/CT showed high sensitivity for both phaeochromocytoma and paragangliomas. This is partly because of wide spectrum of affinity of ⁶⁸Ga-DOTANOC for SSTR subtypes. On the other hand, uptake of ¹³¹I-MIBG is dependent on the expression of vesicular monoamine transporters (VMAT 1, 2). Expression of VMAT is high in benign phaeochromocytoma but is reduced in malignant phaeochromocytoma and paragangliomas.[5] In our case study, ¹³¹I-MIBG scintigraphy and ⁶⁸Ga-DOTANOC PET/CT both showed increased tracer uptake in metastatic pheochromocytoma. This case demonstrates unusual site of omental metastasis in malignant pheochromocytoma. Occurrence of the extra-adrenal paragangliomas outside the normal distribution of the paraganglionic tissue can probably be explained by the migratory property of the neural crest cells during embryogenesis.[67] These cells can form collection of paraganglionic tissue and give rise to paragangliomas. The recurrent lesions in our case were positive both on ¹³¹I-MIBG scintigraphy and ⁶⁸Ga-DOTANOC PET/CT. But ¹³¹I-MIBG was strongly positive, which altered the patient management, and the patient was taken for ¹³¹I MIBG therapy.