A 40-year-old male presented with right mid thigh swelling.
A 40-year-old male presented with right mid thigh swelling. There was no history of trauma or pyrexia. No significant past medical history could be elicited. Physical examination revealed a vague swelling at the ventral aspect of the right thigh that was soft to firm and non tender on deep palpation. The overlying skin appeared normal with no erythema or local rise in temperature. Plain radiographs of the thigh revealed a well defined soft tissue density mass in the thigh which was displacing the adjacent fat plane. There was no intralesional calcification or phleboliths. Subtle pressure remodelling of the underlying femoral shaft could be seen. However there was no periosteal reaction seen along the femoral shaft. He was further evaluated with contrast enhanced MRI of the thigh. MRI showed a well circumscribed, lobulated, homogeneous, intramuscular mass without significant surrounding oedema in the vastus medialis muscle of the thigh. It was homogeneously hypointense on T1-w and hyperintense on the T2-w images. The T1-w images showed a perilesional fat cap along the caudal margin of the lesion. This fat cap was also well visualised on the T2-w images. On post contrast scan the lesion demonstrated homogeneous enhancement. Adjacent bone demonstrated normal marrow signal intensity. Based upon the imaging findings of intramuscular location of a well-circumscribed fluid-signal-intensity mass with perilesional cap of fat and homogeneous contrast enhancement, the possibility of intramuscular myxoma was considered and confirmed on biopsy.
Intramuscular myxoma (IM) is a relatively uncommon benign tumour of connective tissue that presents as a slow growing intramuscular mass. These are thought to arise from modified fibroblasts which produce abundant mucopolysacharide. Macroscopically, IMs are well circumscribed, lobulated and gelatinous in morphology. On histopathology IMs are chiefly composed of polyhedral and stellate cells that are loosely embedded in an avascular myxoid or mucoid matrix, thereby resembling primitive mesenchymal tissue. At times, IMs can demonstrate areas of increased cellularity and vascularity that can lead to erroneous diagnosis of sarcoma, particularly myxofibrosarcoma/ fibromyxoid sarcoma/ or myxoid liposarcoma. The majority of cases are solitary, though multiple lesions may be encountered in patients with Mazabraud's or Albright's syndrome. These tumours typically present as a slowly increasing painless, deep-seated intramuscular mass involving the proximal thigh, gluteal region, upper limb, calf or the shoulder girdle. They are mostly encountered in fourth to sixth decades of life with a distinct female predilection.
On ultrasonography, IM is seen as a well circumscribed hypoechoic intramuscular mass with or without internal cystic areas. On CT, it is seen as a hypoattenuating mass without any calcification or heterogeneity. A variable amount of enhancement may be seen on contrast study. The juxtra-muscular fat planes appear normal. MRI features of IM are characteristic and reflect the high mucin and low collagen content of the lesion. IM is seen as a well circumscribed lobulated mass with sharply defined borders confined to a skeletal muscle. It demonstrates fluid signal characteristics on plain MRI i.e. signal intensity lower than skeletal muscle on T1-weighted images and brighter than fat on T2-weighted images. Mostly the signals are homogeneous on both T1 and T2-weighted images. A variable degree of lesion enhancement may be encountered mostly avid and heterogeneous owing to intralesional cystic areas. Similar signal characteristics may be encountered in other soft tissue masses such as ganglion, neurofibroma or myxoid liposarcoma. These are however located along the intermuscular plane rather than being intramuscular. Furthermore, Bancroft et al found that the identification of a perilesional fat rind on T1-weighted MRI and of increased signal intensity of the adjacent muscle on T2-weighted images increases the likelihood that a lesion is a myxoma and not a myxoid liposarcoma.
To conclude, a well-defined intramuscular lobulated mass demonstrating fluid signal intensity on T1-and T2-w images and a perilesional fat cap or perilesional T2-hyperintensity should suggest the diagnosis of intramuscular myxoma and prevent other erroneous diagnosis of myxoid liposarcoma.
Intramuscular myxoma of the vastus medialis
Based on the X-ray, MRI images, and clinical information provided by the patient, a clearly demarcated, lobulated soft tissue mass is observed in the deep soft tissue of the mid-right thigh. Key points are summarized as follows:
Taking into account the patient’s age (40 years), clinical symptoms (thigh swelling, slow progression), and imaging characteristics (high myxoid component, well-defined margin, high T2 signal, etc.), the following major considerations or differential diagnoses are presented:
Based on the patient’s age, clinical manifestations, and imaging features (intramuscular location, myxoid phenotype, clearly lobulated boundaries, heterogeneous enhancement, and intact perifascial fat), the most consistent diagnosis is:
Intramuscular Myxoma.
A definitive histopathological diagnosis can be established via ultrasound-guided or CT-guided biopsy if necessary, to exclude other types of soft tissue sarcomas.
Given that this lesion is located in the thigh muscle, the following rehabilitation and exercise principles are offered for reference:
Disclaimer: This report is a reference-based medical analysis and cannot replace in-person consultations or specialized clinical advice. If you have any doubts or changes in your condition, please consult a specialist or visit a healthcare facility promptly.
Intramuscular myxoma of the vastus medialis
