Tracing chameleon: thallium-201 SPECT/CT for pheochromocytoma

A 61-year-old woman, in receipt of haemodialysis for 11 years, was diagnosed with a high-grade papillary urothelial carcinoma of the urinary bladder. Thallium-201 single photon emission computed tomography/computed tomography (SPECT/CT) was performed during the cancer work-up (Figure 1). Unenhanced CT images of the SPECT/CT demonstrated a left adrenal mass (31.7 mm in size) with a homogeneous density of 62 HU. Scintigraphic SPECT images of the SPECT/CT showed an abnormal focus of increased radiotracer activity in the left upper quadrant of abdomen. The corresponding SPECT/CT fusion images confirmed the focus in the left adrenal medulla. The patient underwent a left adrenalectomy and the pathological findings indicated the histological characteristics of pheochromocytoma (Figure 2). Pheochromocytoma is a rare catecholamine-secreting tumour with a potential for cardiovascular devastation if the diagnosis is overlooked. The tumour may present with a diversity of imaging features that result from various histological degenerations including fibrosis, calcification, congestion, haemorrhage, necrosis and cystic change. Therefore, pheochromocytoma is often referred to as an epithet ‘imaging chameleon’ [1]. An adrenal mass with attenuation value >10 HU on CT usually suggests a radiological diagnosis of pheochromocytoma. Thallium201, a widely used radiotracer for myocardial perfusion scintigraphy, has been proved effective in the diagnosis