Demonstration of the use of SPECT-CT in a case of pheochromocytoma

Clinical History

The patient had a diagnosis of adrenal pheochromocytoma confirmed by 123I-mIBG SPECT-CT prior to surgical resection.

Imaging Findings

Our 50 year old patient, who was suffering from hypertension and type II diabetes requiring insulin, was found to have a 8.2cm, well defined, mixed echogenicity, partly cystic left suprarenal mass on abdominal ultrasound. Subsequent contrast-enhanced arterial and renal parenchymal phase helical CT revealed that the mass was related to the adrenal gland. Chemical shift MRI excluded an adrenal adenoma. Due to raised urinary catecholamines and vanillylmandelic acid (VMA) the mass was strongly suspected to be a pheochromocytoma. Subsequently, SPECT-CT was performed (Siemens SymbiaT 2-slice, dual scintillation detector). 370MBq of 123I-metaiodobenzylguanidine (mIBG) was administered with SPECT-CT carried out at 4 hours post injection, at 5mm slice thickness and 128 frames at 20 seconds/frame on a 128x128 acquisition matrix, and whole body planar imaging at 24 hours. Intense uptake of mIBG by the adrenal mass confirmed the diagnosis. No extra-adrenal lesion or metastases were identified.

Discussion

Pheochromocytoma is a rare tumour of neural crest origin which occurs mainly in adults. 85-90% arise from the adrenal medulla. Whether benign or malignant, surgical resection is the only cure and accurate pre-operative staging is mandatory. Current recommendations for imaging of pheochromocytoma takes account of the difficulty in predicting its malignant potential and should include anatomical delineation by CT and functional imaging to identify unsuspected metastases. [1]
mIBG is an analogue of a noradrenaline precursor stored in the cells of organs with rich adrenergic innervation. Labelled with an iodine radioisotope it provides an ideal marker for the identification of pheochromocytoma and other tumours of neural crest origin. 123-I has more favourable characteristics as a radioisotope in nuclear imaging than 131-I with regard to image noise, dosimetry and scan timing.
Standard planar mIBG scintigraphy has a sensitivity of 87.5% and specificity of 99% in the detection of pheochromocytoma. [2] A previous study has demonstrated increased diagnostic accuracy using SPECT/CT versus standard planar mIBG scanning in detecting these tumours. [3] Contrast enhanced CT reportedly has a sensitivity of 92% and specificity of 80% in diagnosis of pheochromocytoma. A further study recently demonstrated that SPECT/CT provided additional information in 53% of cases of pheochromocytoma or neuroblastoma compared to CT alone. [2]
Overall, SPECT/CT has emerged as a dual modality technique which is becoming widely accepted as having multiple clinical applications. It allows tomographic scintigraphic and CT images, acquired sequentially on a hybrid scanner, to be co-registered allowing direct correlation between the high resolution morphological detail of CT and the pathophysiological state of the lesion in question. In the case of an adrenal lesion it can differentiate between a functioning and non functioning mass and in our case, using a 123I-mIBG tracer, allowed confident confirmation of an adrenal pheochromocytoma while excluding concurrent extra-adrenal lesions or metastases.

Differential Diagnosis List

Final Diagnosis

pheochromocytoma confined to the adrenal gland

URL:	https://www.eurorad.org/case/7213
DOI:	10.1594/EURORAD/CASE.7213
ISSN:	1563-4086