Extracardiac abnormality on myocardial perfusion imaging - liver metastasis
Presentation
Chest pain.
Patient Data
Myocardial perfusion scan
Process short axis (SA), vertical long axis (VLA) and horizontal long axis (HLA) images show no stress perfusion defects or evidence of ischaemia.
Raw data reviewed for quality control shows an abnormally large photopenic defect in the right lobe of the liver (just lateral to the gall bladder).
A CT of the abdomen from 2 years prior (not shown) demonstrated no abnormality and hence further imaging was recommended.
Follow-up CT of the liver obtained 2 days later demonstrates multiple irregular hypodense lesions, some calcified, predominately in the right lobe, corresponding with an abnormality detected on preceding MPS. The lesions demonstrate enhancing walls and septations, most concerning for cystic metastases.
Case Discussion
The largest liver lesion was biopsied and found to be a mucinous gastrointestinal metastasis of unknown primary.
Numerous reports in the literature described the identification of lung cancer, breast cancer, lymphoma, thyroid neoplasms and thymoma as unexpectedly increased extracardiac radiotracer uptake on MPS exams. In contrast, this case demonstrates an occult extracardiac tumour identified due to the absence of normal radiotracer uptake on the MPS exam.
Myocardial perfusion scintigraphy agents are extracted from the blood pool by the liver and subsequently excreted into the biliary tree and bowel. Hence, there should be normal homogenous activity throughout the liver. An area of decreased or absent hepatic uptake should be noted and raises the possibility of a space-occupying lesion (SOL). While most of these will likely represent benign cysts, further imaging with US or other modalities may be warranted to definitively assess the abnormality.
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