Weekly Case

Title : Case 631

Age / Sex : 49 / M

Chief complaint :

Mild firm and painful mass in left calf. (2 days ago)

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : 
Jang Gyu Cha, Soonchunhyang University Bucheon Hospital



Answer: Proliferative myositis




Lower leg MR;  

T2-weighted spin-echo MR images of the left lower leg show a hyperintense soft-tissue mass in the belly of the medial head of gastrocnemius muscle preserving the muscle fibers. T1-weighted MR image demonstrate intermediate to subtle high signal intensity and almost homogenous enhancement.  


Lower leg USG;

Irregular hyperechoic mass with intra-lesional hypoechoic line.


Differential Diagnosis:  


soft-tissue tumors, traumatic injury, myositis ossificans, muscle sarcoidosis, and various causes of infectious and inflammatory processes




Proliferative myositis(PM) is a rare benign inflammatory myopathy characterized by infiltration with basophilic giant cells and proliferative fibroblasts.


The keys to assigning the correct diagnosis are patient age, history of recent trauma, and a rapidly growing, firm and painful soft-tissue mass.  

-Clinically, it presents as a very rapidly growing solitary soft-tissue mass, with or without pain.

-The etiology is unknown, but there is often a history of local trauma.

-It occurs most commonly in adults (mean age, 50 years), although it has been described in children.

-It usually arises in the trunk, head and neck region or in the upper extremities.



Ultrasonography and computed tomographic (CT) findings are nonspecific. CT usually reveals a mass that is hypo- or isoattenuating relative to the skeletal muscle, and contrast enhancement may be homogeneous, heterogeneous, or absent.  

MR images of PM have been reported in several cases, with a hypo- or isointense T1 signal compared with that of muscle and homogeneous enhancement. T2-weighted MR images typically demonstrate a hyperintense soft-tissue mass.


Once the diagnosis has been established, the recommended follow-up strategy is no specific treatment, since PM may disappear spontaneously. Excision may be preferred to establish a diagnosis and for cosmetic reasons. Recurrence is extremely rare.




Radiology 2007; 244:613– 616. Case 118: Proliferative Myositis.

Skeletal Radiol. 2004; 33(4):237-240. Proliferative myositis in a patient with AIDS.

Correct Answer
Total applicants 32 Correct answers 2
Name Institution
장민영 국민건강보험공단 일산병원, 전문의
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