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.