CT imaging features of skeletal muscle metastasis

To define the computed tomography (CT) features common in skeletal muscle metastases and their prevalence and to identify the most commonly associated primary malignancy and the most common muscle groups in which skeletal muscle metastases are found.

Institutional review board (IRB) waiver for informed consent was obtained. A retrospective review was conducted of CT examinations from a single, large, academic centre picture archiving and communication system (PACS) database, performed from August 2009 to July 2013. All 10,426 examinations and 8,524 unique patients reviewed had a confirmed diagnosis of malignancy. The CT reports were screened manually to identify disease involving the skeletal muscles. Images of the 60 initial studies identified were then reviewed. Cases that showed direct invasion of the tumour into the skeletal muscles, and follow-up studies of the same patient were excluded. The 27 included cases were classified under five distinct patterns.

In the present study, the prevalence for skeletal muscle metastasis was 0.33% across all malignancies. The most common primary involved was breast cancer (25%). The most common pattern was focal intramuscular mass with homogeneous contrast enhancement. The most common sites of skeletal muscle metastasis were in the abdomen (43%) and thorax (33%) musculature.

Breast cancer was the most commonly associated primary malignancy and a focal, homogeneously enhancing intramuscular mass was the most common presentation. Although skeletal muscle metastasis remains a rare entity, its incidence rate should increase with the increased usage of whole-body PET CT for cancer staging.