1. INTRODUCTION
Intramuscular myxoma (IMM) are benign soft tissue that account for 0.1
to 0.13 per 100,000 populations (1). Various theories have been
described regarding the mechanism of IMM occurrence. Some researchers
suggest that the reason is fibroblasts (unable to synthesize collagen
fibers) that are not well differentiated from mesenchymal stem cells,
which cause the synthesis of myxoid stroma without reticular fibers.
Others consider the etiology of IMM to be caused by traumatic mechanisms
or the growth of polysaccharide-producing cells in the neoplastic
process (2). IMM is rare and can occur in the buttocks, thigh, upper
extremities and shoulder muscles. Epidemiologically, its occurrence rate
is higher in women (70%), increases with age (6th and 7th decade of
life) and the most common sites of IMM is upper extremities muscles
(50%-60%) (3). According to the location of the masses, soft-tissue
myxomas are classified into superficial angiomyxoma, intramuscular
myxoma, nerve sheath myxoma and aggressive angiomyxoma. From the
clinical point of view, IMM is a palpable mass, painless, without
inflammatory secretions and symptoms, which has no contractile
properties and no stretch-contraction changes during flexion-extension
of the adjacent muscles (4).
From a diagnostic point of view, IMM is observed as a non-calcified mass
in plain radiograph, which is seen in the supplementary findings with
the help of ultrasonography as echogenic cystic lesions among the muscle
tissue. The most important diagnostic method of IMM from other soft
tissue lesions is magnetic resonance imaging (MRI), which can be seen as
hypointense homogeneous mass in T1-weighted sections and hyperintense in
T2-weighted sections (5). In case of edema with IMM in MRI sections
(T1-weighted sections), it should be differentiated from other
fluid-containing lesions (such as cystic teratoma, hematoma, myxoid
sarcoma, cystic hygroma and even normal lymph nodes). Also, IMM should
be differentiated from proliferative lesions, other myxoid neoplasms,
myxochondroma, myxochondroma and myxoid liposarcoma (6).
Cytology-histopathology findings with the help of intraoperative frozen
section and needle biopsy help the information of MRI sections in the
diagnosis of IMM. Density and ratio of cells/ collagen fibers, mucoid
material secretion, nodular-vesicular pattern and fat density in
histopathological sections contribute to IMM (7). In the present case,
forearm intramuscular myxoma was observed inter-supinator muscle.