Differential diagnosis
Differential diagnosis of forearm mass in MRI evaluation with high water content (mimicking a cyst) include synovial cyst, ganglion, bursa, neurogenic tumor, myxoid liposarcoma, and malignant fibrous histiocytoma. The majority of synovial cysts, bursae, and ganglia occur at typical locations such as the popliteal fossa and dorsal aspect of wrist. These lesions typically are seen in intermuscular planes, whereas most soft tissue myxomas are intramuscular in location. Also, as compared to intramuscular myxoma, these lesions show a cystic nature with peripheral rim enhancement and delicate septae only seen on postcontrast computed tomography and MRI images. Ultrasonography, these lesions show an anechoic component as compared to IMM, which are hypoechoic in echotexture, with posterior acoustic enhancement and no anechoic component. Neurogenic tumors are also typically located in the intermuscular compartment. A nerve entering and exiting the lesion is usually appreciated at the margins of the lesion. These imaging findings are not seen in IMMs. Similarly, myxoid liposarcomas are usually intermuscular lesions developing in the subcutaneous fatty tissue, unlike soft tissue myxomas. In addition, myxoid liposarcomas usually contain small amounts of intrinsic fat. In this respect, the IMM may have some imaging features similar to myxoid liposarcoma. Myxoid malignant fibrous histiocytomae are intramuscular lesions similar to myxomas, however these lesions show far more heterogenous appearance on imaging, with areas of hemorrhage. These lesions also show some solid nodular component with prominent contrast enhancement, whereas the myxomas show moderate, relatively homogenous enhancement.
During surgery, a longitudinal incision was made in the anterior area of the elbow joint on the supinator muscle at the site of the tumor lesion and the encapsulated mucoid-gelatinous gray myxoid mass 3.5 × 2.5 × 2 cm was removed from the muscle.