A 48-year-old woman complaining of non-painful tumoration at her left thigh.
A 48-year-old woman complaining of non-painful slowly enlarging tumoration at her left thigh. She was submitted to magnetic resonance imaging (MRI). MRI examination revealed that tumor was located in the left lateral vastus muscle. The tumor was essentially isointense on T1weighted images and markedly hyperintense on Proton Density Fat Sat images. A prominent enhancement effect with intravenous gadolinium administration was detected. After surgical resection, the pathological diagnosis confirmed an intramuscular myxoma.
Primary myxomas are rare, benign mesenchymal neoplasms. The vast majority of cases arose in the intramuscular compartment (82%) of the thigh (51%), upper arm (9%), calf (7%), or buttock (7%) (1). Only a small number of cases were intermuscular (9%), subcutaneous (9%), or juxtaarticular (7%) (1). The most common clinical history was that of a slowly enlarging soft-tissue mass (1). The tumors can be seen at any age, occurring most commonly during the fifth and sixth decades of life, and there is a slight female predominance (2). The plain film can be normal, show a soft tissue mass or, rarely, show calcifications within it (3). Due to its hypovascular nature, IM shows a mild uptake on scintigraphic studies and either poor or moderate vascularity on angiography , although a moderate vascularity has been related to an increase in the cellularity (3). A well-demarcated hypoechoic or anechoic mass with multiple cystic areas or fluid-filled clefts in an intramuscular location is the typical presentation on ultrasound (3). On computed tomography, IM is shown as a well-defined, homogeneous mass with attenuation values between those of water and muscle (3). In clinical practice, MR imaging findings raise the suspicion of IM in cases of an intramuscular mass with a very sharply defined contour and cystic appearance on unenhanced sequences, with peripheral and a variable degree of internal enhancement on post-contrast images, and possibly the identification of intratumoral cystic areas. The most distinctive features of IM are the identification of a perilesional fat ring and the presence of edema in adjacent muscles (2, 3,4). Intramuscular myxomas have frequently been misdiagnosed as malignant soft tissue tumors (5), because of the rareness, deep localization, greater mass than 3 cm diameter, and histological similarity to myxoid liposarcoma, or myxoid malignant fibrous histiocytoma (MFH), sometimes rhabdomyosarcoma, although the duration of the clinical symptoms are usually longer than one year (5). The differential diagnosis (1) of a lesion with imaging findings of a soft-tissue mass and high water content that mimics a cyst includes the following: synovial cyst, bursa, ganglion, neurogenic neoplasms, myxoid liposarcomas, and myxoid MFH (1). The vast majority of synovial cysts, bursae, and ganglia occur in well-recognized locations and are intermuscular masses, whereas most soft-tissue myxomas are intramuscular (1). In contradistinction to myxoma, these lesions represent truly cystic masses that can be recognized by the abscence of internal enhancement or by their anechoic appearance at US (1). Neurogenic neoplasms, both benign and malignant, are also typically intermuscular lesions. Unlike soft-tissue myxoma, myxoid liposarcoma is also usually an intermuscular lesion and often contains a small amount of intrinsic fat. Myxoid MFH, like soft-tissue myxoma, is typically an intramuscular lesion; however, myxoid MFH usually has a far more heterogeneous appearance at imaging, with areas of hemorrhage and solid nodular regions that may reveal prominent contrast enhancement (1). The association of myxomas with fibrous dysplasia is known as Mazabraud’s syndrome and has led to the proposal that there is an underlying localized error in connective tissue metabolism (1).
Intramuscular myxoma
Patient Information: 48-year-old female with a painless mass in the left thigh.
Based on the provided MRI images and the patient's description, the main radiological features are as follows:
Taking into account the imaging features and the patient’s history, the following are potential (differential) diagnoses:
In summary, the patient is a 48-year-old female presenting with a slowly enlarging, painless mass within the left thigh muscle. The imaging features suggest an intramuscular lesion rich in myxoid components without obvious malignant enhancement or hemorrhage. Based on literature and typical presentations, the most likely diagnosis is “Intramuscular Myxoma.”
For a definitive diagnosis, a biopsy or surgical excision followed by pathological examination is recommended, in order to rule out myxoid liposarcoma and other malignant soft tissue tumors.
If surgery is undertaken, postoperative rehabilitation will focus on minimizing local swelling, restoring muscle strength, and maintaining joint range of motion. If conservative observation is chosen, moderate muscle exercises can help maintain lower-limb function. Adhering to the “FITT-VP” principle is advisable for a gradual progression:
Note: After surgery, strengthening exercises should start only after sutures are removed and adequate tissue healing is confirmed to avoid tension or wound dehiscence.
This report is based on the limited information provided, and it serves as a reference for analysis only. It does not constitute a legally valid diagnosis or treatment prescription. A definitive diagnosis and treatment plan require an in-person clinical evaluation, necessary laboratory and pathological examinations, and the guidance of a specialist physician.
Intramuscular myxoma
