Intramuscular myxoma of the long adductor muscle of the thumb

Clinical History

A rare localization of intramuscular myxoma is decribed and surgically treated after Ultrasound investigation.

Imaging Findings

The authors report on a male patient with a rare localization of intramuscular myxoma (IM). The clinical examination found out a painless soft-tissue mass. The tumefaction was located near the distal insertion of the long adductor muscle of the left thumb. Ultrasound examination (15 Hz.) revealed an oval-shaped lesion, with dishomogeneous echostructure, clearly distinguished by surrounding normal muscular structures which sized 3.5 x 2.0 x 1.0 cm (Fig.1 arrows). Color Doppler US showed poor vascularity around the lesion. The iperechogenic line which corresponded to the proximal phalanx was regular and clearly posteriorly depicted. The lesion was excised surgically. At the operation the specimen appeared quite well circumscribed and lobulated. Histology examination showed uniform stellate-shaped cells, separated by an abundant myxoid matrix. These results led to a correct diagnosis.

Discussion

IM is a relative benign tumour of the soft tissues, whose origin is still unknown. One assumption is that it originates from fibroblasts which are not sufficiently differentiated and thus not able to sintetize collagen. Another hypothesis implicates mesenchymal pluripotent cells [1]. The common clinical form is a painless relatively large, slowly growing mass without anamnestic trauma. IM is well circumscribed, lobulated and gelatinous; its size may be up to 20 cm, but commonly <10 cm. IM is most usually found in the large muscles of the thigh and buttock, lower leg, shoulder and upper arm. Females are more frequently affected, especially between 4th and 7th decades of life. The peculiarity of our case is the localisation and the age of the patient (a 23 year old male) never before reported in literature. Histological areas of incresased cellularity and vascularity must be evaluated with precaution, to avoid misdiagnosis with the myxoid sarcoma, myxofibrosarcoma and low-grade fibromyxoid sarcoma [2]. Clinical examination is not specific and a definite diagnosis can be established only by accurate histological examination. US is a basic support, in making a quick differential diagnosis between solid and cistic lesions, defining dimensions, and is a useful mean in follow-up. Although in clinical practice , MR imaging allows better characterization and better local staging in muscle – skeletal lesions. The advantage of MR imaging represents the elective investigation to provide a valid diagnostic support thanks to its optimal soft tissue resolution, cross – sectioning and defines connections with nearby tissue.

Differential Diagnosis List

Final Diagnosis

Intramuscular myxoma

URL:	https://www.eurorad.org/case/1007
DOI:	10.1594/EURORAD/CASE.1007
ISSN:	1563-4086