Paraganglioma

Rebecca T Leibowitz, MD - Case Coordinator
Amy Ho Huang, MD - Radiology Discussion
Kimberley M Springer, MD - Pathology Discussion
Steven E Seltzer, MD - Attending Radiologist

December 8, 2003

Presentation

Imaging Findings

The single axial CT image (with oral but no intravenous contrast) demonstrates a well-circumscribed, 4-5 cm ovoid soft-tissue mass just anterior and superior to the iliac bifurcation at the expected location of the Organ of Zuckerkandl. The mass could be arising from sympathetic nervous system tissue or represent enlarged lymph nodes or a mass in the small bowel. It does not appear to invade adjacent structures.

Diagnosis

Discussion

The gross specimen is a delicately encapsulated, 6-cm mass. It is red-brown in color and has a somewhat cystic appearance. There is no necrosis and lymphovascular invasion is not definitively identifiable. Microscopsy reveals nests of lobular cells that, on staining, are positive for chomogranin and synaptophysin. Further staining for S100 protein highlights sustentacular cells. The mitotic rate is as high as 3:50 HPF (high-power field).

Radiology Discussion

Pheochromocytoma is an uncommon (prevalence 0.13%) neoplasm of chromaffin cells. The tumor secretes catecholamine; presenting symptoms include palpitations, diaphoresis and headache. It is often suspected in young hypertensive patients or in the presence of refractory/labile hypertension. Nearly 90% of these tumors originate in the medulla of the adrenal glands. The remaining 10% are extra-adrenal; the preferred term for extra-adrenal pheochromocytoma is paraganglioma. These usually arise in the organ of Zuckerkandl, located at the aortic bifurcation.

Pheochromocytoma is said to follow the “rule of 10s,” which states that 10% are extra-adrenal (aka paraganglioma), 10% are bilateral, 10% are extra-abdominal, 10% are malignant, 10% are familial (VHL, NF 1, MEN 2A/2B), 10% are pediatric, and 10% are not associated with hypertension.

The first-line clinical tests for the common presenting symptoms include plasma catecholamine levels and 24h urine vanillylmandelic acid and metanephrine levels. These tests are 89-100% sensitive. When pheochromocytoma is suspected on clinical and laboratory grounds, CT is the study of choice to confirm the diagnosis. The typical appearance on CT is a heterogeneously enhancing adrenal mass >3cm; calcifications are sometimes present. If an adrenal mass is identified on CT, treatment is surgical resection. If an adrenal mass is not seen, the paraspinous region should be investigated. Magnetic resonance imaging is useful for detecting extra-adrenal pheochromocytoma (paraganglioma) and recurrence after resection. The tumors tend to be hyperintense on T2-weighted images, though not all have this characteristic.

Nuclear Medicine is used when pheochromocytoma is suspected but no mass is identified on CT or MR. Two different radiotracers may be used. I-131 MIBG is an analog of norepinephrine, which is stored in the adrenal medulla. In this type of study, imaging is performed 24-72 h after radiotracer administration. Any focal uptake in the adrenal gland is abnormal. This study will also detect extraadrenal pheochromocytoma, metastases, and residual tumor after surgery. It is 85% sensitive and 96% specific. In-111 octreotide is an analog of somatostatin that shows uptake in tumors that contain somatostatin receptors. In this study, whole body imaging is performed 4-24 hours post injection. It is 75-90% sensitive. While 50% of pheochromocytomas can be detected by either type of study, 25% are revealed only with I-131 MIBG and 25% are seen only with In-111 octriotide.

References

Mayo-Smith WW, Boland GW, Noto RB, Lee MJ. State-of-the-art adrenal imaging. Radiographics 2001 Jul-Aug;21(4):995-1012.

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