Hyperfunctioning Adrenal Medullary Neoplasms

1-Pheochromocytoma is a neoplasm of adrenal medulla.

2-They are typically unilateral and benign, but it could be bilateral and malignant in 10% of cases.

3-The tumor secretes catecholamines.

4-It causes hypertension.

5-Clinical diagnosis : younger patient with hypertension.

5-Laboratory diagnosis : Plasma catecholamine levels and 24-hour urine vanillylmandelic acid and metanephrine levels.

6-

When a pheochromocytoma is suspected on clinical and laboratory grounds, CT is the study of choice to confirm the diagnosis. Typically, an adrenal mass is identified at CT (Fig 4). Three-dimensional imaging and coronal reconstructions may be helpful to demonstrate adjacent vessels, particularly with the recent advent of laparoscopic adrenalectomy .

If an adrenal mass is identified at CT in a patient with a suspected pheochromocytoma, the treatment is surgical resection. 

If an adrenal mass is not seen, attention should be directed to the paraspinous region because 10% of pheochromocytomas are extraadrenal. Paraganglioma is the preferred term for such tumors, rather than extraadrenal pheochromocytoma.

The MR imaging appearance of a pheochromocytoma has typically been described as T2 hyperintense (Fig); however, not all pheochromocytomas have this imaging characteristic. 

MR imaging is useful for detecting extra adrenal paragangliomas and recurrences after resection, given their increased signal intensity on T2-weighted images. 

For patients in whom a pheochromocytoma is suspected and an adrenal mass is not identified at CT or MR imaging, nuclear medicine imaging can be used. 

I-131 MIBG and In-111 octreotide are the two radiopharmaceuticals used to evaluate for a pheochromocytoma. 

I-131 MIBG is a structural analog of norepinephrine, which is stored in neurosecretory granules of the adrenal medulla. Abdominal imaging is performed 24–72 hours after administration of the agent, and whole-body imaging should be performed to detect extraadrenal lesions. If there is a high clinical suspicion of a perivesicular paraganglioma, bladder catheterization may be necessary as the agent is excreted in the urine.

When pheochromocytoma is suspected, any focal uptake of I-131 MIBG in the adrenal gland is abnormal (Fig).

Pheochromocytoma in a patient evaluated with nuclear medicine imaging. Posterior image obtained 48 hours after intravenous administration of I-131 MIBG demonstrates increased activity in the right adrenal gland (arrow).

The reported sensitivity of I-131 MIBG for detection of a pheochromocytoma is 80%–90%, with a specificity of 90%–100%. 

I-131 MIBG scintigraphy is useful to detect the 10% of pheochromocytomas that are extraadrenal and to document metastatic disease or residual tumor after surgery. 

In-111 octreotide, the second agent used to detect pheochromocytomas, is a synthetic octapeptide analog of somatostatin that shows uptake in a variety of tumors that contain somatostatin receptors.

A total of 5 mCi (185 MBq) of In-111 octreotide is administered intravenously, and whole-body imaging is performed at 4 and 24 hours after injection. In-111 octreotide has a sensitivity of 75%–90% for detection of pheochro-mocytomas.

There is a complementary role for In-111 octreotide and I-131 MIBG, since 25% of pheochromocytomas are seen only with I-131 MIBG and another 25% are seen only with In-111 octreotide. The remaining 50% of pheochromocytomas are visualized with both agents. 

Pheochromocytoma in a 30-year-old man evaluated with CT. (a) Contrast-enhanced axial CT scan demonstrates an enlarged right adrenal gland with internal calcifications (arrow). (b) Coronal reformatted image from the axial data set demonstrates the relationship of the right adrenal pheochromocytoma (arrow) to the upper pole of the right kidney and the liver.