Fatima Soliman MD, PhD, Presenter: Nothing to Disclose

Sinchun Hwang MD, Abstract Co-Author: Nothing to Disclose

Jonathan Landa DO, Abstract Co-Author: Nothing to Disclose

Robert Andrew Lefkowitz MD, Abstract Co-Author: Nothing to Disclose

David M. Panicek MD, Abstract Co-Author: Nothing to Disclose

To determine the prevalence of an unusual, infiltrative pattern of primary carcinoma metastatic to muscles of an extremity, which sometimes mimics myositis at MRI.

This retrospective study was IRB and HIPPA compliant. The reports of extremity MRI exams of 907 patients with a proven diagnosis of carcinoma from a recent two-year period were reviewed to identify those that mentioned muscle metastasis or myositis in an extremity. Pathology reports, follow-up imaging, and clinical records were used to confirm the diagnosis of metastasis. MR images from each patient with muscle metastasis then were reviewed by two radiologists in consensus to record whether the metastases manifested as discrete masses or as an infiltrative process (i.e., carcinomatosis).

36 (4%) of 907 MRI reports described muscle metastases (n=18) or myositis (n=18), in 25 males and 11 females (mean age, 64 yrs; range, 33-83 yrs). After review of the medical records, three cases reported as myositis were found to actually represent muscle metastases. Metastases manifested as discrete masses at MRI in 16 (76%) of 21 patients; in each of the remaining 5 (24%), the metastases showed extensive infiltration of multiple muscles. All five (100%) cases of carcinomatosis of muscle were caused by primary esophageal (n=3) or gastric (n=2) cancers. One such case was proven by biopsy; in the other four patients, the lesions were determined to represent metastases based on follow-up imaging and clinical course. Only two of the five cases were correctly diagnosed as carcinomatosis of muscle in the original MRI report; the other three cases of carcinomatosis had been misdiagnosed as myositis. The most common types of primary carcinoma resulting in discrete muscle metastases were lung (4/21=19%) and kidney (4/21=19%).

Muscle metastases usually manifest as discrete masses at MRI, with primary lung or renal cancers being the most common sources. An infiltrative pattern, representing carcinomatosis of muscle, is uncommon; typically results from primary esophageal or gastric cancers; and may mimic myositis at MRI.

Esophageal and gastric cancers uncommonly metastasize to multiple muscles of an extremity as infiltrative carcinomatosis, which may be misdiagnosed as myositis at MRI.

Soliman, F, Hwang, S, Landa, J, Lefkowitz, R, Panicek, D, Carcinomatosis of Muscle: A Potential Mimic of Myositis.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14006981.html