A Case of Incidentally Detected Silent Adrenal Pheochromocytoma, Mimicking as an Intraperitoneal Tumor With Unusual Computed Tomography Findings

Pheochromocytoma is a rare catecholamine secreting tumor arising from chromaffin cells (1). They are mostly benign with a prevalence of 0.2%–0.6% (2, 3). Signs and symptoms may vary; although, in more than 50% of patients with pheochromocytoma, high blood pressure is predominantly associated with secretion of norepinephrine (4, 5). A diagnosis usually starts with patient presenting with hemodynamic instability followed by biochemical examination and computed tomography (CT) of abdomen.

However, pheochromocytoma may be present as an asymptomatic adrenal incidentaloma and only detected by cross-sectional imaging (6). The term silent pheochomocytoma has been used for such clinical incidence (7, 8). In this report, we presented a case of incidentally found silent pheochromocytoma mimicking as an intraperitoneal tumor, such as gastric gastrointestinal stromal tumor-like appearance on CT scan, with accompanying tumor shrinkage during follow-up.

A 39-year-old female patient was referred to our center after failure to remove intra-abdominal tumor at another hospital. The patient initially presented with an acute abdominal pain. She had no history of underlying diseases, including hypertension and cardiovascular symptoms. An initial CT scan revealed an intra-abdominal tumor measuring 5.2 cm in the left abdomen (Fig. 1). Under the suspicion of gastric gastrointestinal stromal tumor, a diagnostic surgery was performed via laparoscopic peritoneal approach. However, at the beginning of the surgery, the patient experienced hemodynamic instability, with systolic blood pressure spiking up to 180 mmHg. After a brief inspection, the surgical team recognized that the tumor was located in the retroperitoneal space and terminated the surgery. Thereafter, the patient was referred to our center for further evaluation of the adrenal tumor 4 months postoperatively.

Fig. 1
Initial computed tomography scan revealing a 5.2 cm tumor.

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Upon arrival, she reported no abdominal pain. Laparoscopic surgical sites were well healed. The patient underwent a thorough biochemical evaluation associated with pheochromocytoma, including other adrenal functional tumors, yielding unremarkable results. Her hemodynamic status was stable, characterizing by pulse rate of 84/min and blood pressure of 110/66 mmHg. For further evaluation, a follow-up CT scan was performed, which revealed a decrease in the tumor size to 3.2 cm in the longest diameter (Fig. 2). Since hemodynamic instability was encountered during initial surgery at another hospital, we presumed that the patient might have silent pheochromocytoma and prescribed phenoxybenzamine hydrochloride 10 mg per day for a month followed by 10 mg twice a day for 2 weeks before surgery. She underwent retroperitoneal laparoscopic adrenalectomy at 7 months after the initial surgery.

Fig. 2
A follow-up computed tomography scan revealing a decrease in the tumor size to 3.2 cm.

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Second surgery was performed via laparoscopic retroperitoneal posterior approach. During intra-operative examination, a severe adhesion was observed between the adrenal tumor and surrounding tissues suggesting the possibility of adrenocortical carcinoma. Adhesion was particularly noticeable in the peritoneum posterior to the stomach (Fig. 3). The surgery went well with clear resection margins, except at the point of adhesion site having the uncertainty of resection margin safety. The patient’s hemodynamic status remained stable throughout the second surgery. The final pathology confirmed pheochromocytoma measuring 3.3 cm, confined within the adrenal gland, with negative tumor involvement at the resection margin (Fig. 4). Additionally, the pathologic biochemical profile was suggestive of non-secreting tumor. The patient was discharged on postoperative day 3 and is currently recovering without complication. A CT scan performed after the second surgery revealed no remarkable findings, and she is scheduled for a 1-year follow-up appointment at the out-patient clinic, with no medication required.

Fig. 3
(A) Laparoscopic retroperitoneal posterior adrenalectomy procedure and (B) severe adhesion is observed between the left adrenal tumor and peritoneum posterior to the stomach.

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Fig. 4
Specimen of the left adrenal tumor.

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Patients with pheochromocytoma usually present with signs and symptoms, such as headache, palpitation, and high blood pressure (9). However, this patient demonstrated an asymptomatic adrenal incidentaloma until she was prepared for the initial diagnostic surgery. Furthermore, her CT scan presented unusual findings such that initially, it presented as intraperitoneal tumor then during the follow-up, there was a definite size decrease without any hemorrhagic event or rupture of cystic portion. During the second surgery, severe adhesion was observed near the peritoneum posterior to the stomach that lacked an apparent reason to suggest such presentation.

Silent or asymptomatic pheochromocytoma is rare, accounting for 20%–30% of all diagnosed pheochromocytoma cases (10). This patient presented with high blood pressure only at the beginning of the initial diagnostic surgery, at the other hospital, with no other hyperadrenalgic signs or biochemical over-secretion, thereby making it unclear whether the tumor was definitely a pheochromocytoma. Since adrenal tumor larger than 4 cm size is recommended for diagnostic adrenalectomy to eliminate the possibility of malignancy, a second surgery was performed. Despite the absence of hypertensive symptoms, we prescribed adrenergic alpha-receptor blocker before the second surgery. A previous report indicated that a hypertensive crisis can develop even in the case of silent pheochromocytoma surgery when alpha-blocker is not administered; therefore, its preoperative usage still remains as a recommendation (11, 12).

Atypical presentation of silent pheochromocytoma can be encountered in various cross-sectional abdominal images.

Adrenal incidentaloma can be encountered via various cross-sectional abdominal images. When found, biochemical examination is recommended to evaluate the functional disease. Treatment of functional adrenal tumor is surgery. And, an adrenal tumor larger than 4 cm is also a candidate for surgery to eliminate the possibility of malignancy. Silent pheochromocytoma having atypical presentation is one of the candidates for surgical evaluation. When an adrenal incidentaloma having atypical CT scan is identified, surgery should be considered to provide an adequate treatment. Also, preoperative usage of antihypertensive medication should be considered when silent pheochromocytoma is suspected. Additionally, serial CT scans can support the surgeon’s decision of a surgical approach.