# Somatostatin Receptor 2 Negative Pheochromocytoma Masked by Normal Adrenal Gland on Gallium-68 DOTATATE

## TL;DR

A rare case of a pheochromocytoma that was hard to detect using a common imaging technique due to low receptor expression and normal adrenal uptake.

## Contribution

Highlights limitations of 68Ga-DOTATATE imaging for small pheochromocytomas with low SSTR2 expression.

## Key findings

- The pheochromocytoma showed low uptake on 68Ga-DOTATATE imaging due to negative SSTR2 expression.
- Normal adrenal gland uptake masked the tumor in initial imaging, leading to delayed diagnosis.
- Small lesion size and low receptor expression can reduce the sensitivity of 68Ga-DOTATATE for tumor detection.

## Abstract

Gallium-68 DOTATATE (68Ga-DOTATATE) positron emission tomography/computed tomography (CT) is a somatostatin receptor (SSTR)-based imaging with high sensitivity that can be used for detection of pheochromocytomas and paragangliomas. We report a pheochromocytoma with negative SSTR2 expression and low uptake on 68Ga-DOTATATE, whose detection was masked by the uptake of normal adrenal tissue.

A 50-year-old man presented with a right adrenal incidentaloma. He had mildly elevated plasma normetanephrine levels of 194 pg/mL (ref. 0-145 pg/mL). Adrenal CT scan showed a right 1.9-cm lesion with unenhanced attenuation of 38 Hounsfield units. 68Ga-DOTATATE showed a 1.9-cm right adrenal lesion and reported diffuse uptake in the adrenal glands, with maximum standardized uptake value (SUVmax) of 17.23 on the right and SUVmax of 22.78 on the left. After a 2-year interval, plasma normetanephrine level increased to 420 pg/mL (ref. 0-136.8 pg/mL). Adrenal CT scan showed the right adrenal lesion increased in size to 2.6 cm. He underwent right adrenalectomy, and pathology reported a 2.3-cm pheochromocytoma. Subsequent review of the initial 68Ga-DOTATATE identified the pheochromocytoma as a photopenic area in the right adrenal gland with 7.73 SUVmax. Tissue staining was negative for SSTR2 expression. Genetic testing was negative for pheochromocytoma syndromes.

Although 68Ga-DOTATATE has strong affinity for SSTR2, some pheochromocytomas have low expression of SSTR2. The negative SSTR2 expression, small lesion size, and background uptake of the adrenal gland can affect the detection of pheochromocytoma.

68Ga-DOTATATE may have limitations when evaluating small pheochromocytomas or other neuroendocrine tumors with low SSTR2 expression.