Presentation
Left lateral upper thigh lump with slight pain and tenderness with a history of trauma of 4 weeks prior.
Patient Data
A lateral oblique radiograph of the pelvis demonstrates periarticular faint, nodular calcifications with an incomplete ring-like appearance. There is central radiolucency and the noted absence of any osseous connection to the adjacent iliac bone.
By ultrasound, at the lateral aspect of the left hip joint, there is an intramuscular, mass-like lesion (measuring 6 x 5 x 3 cm) with peripheral discontinuous curvilinear calcifications causing distal shadowing with central cystic-like changes.
Scout radiograph of the pelvis, at the level of the left anterior inferior iliac spine and lateral femoral head and neck demonstrates a faint focal lesion with serpiginous calcifications.
Pre-contrast study of the lesion shows linear calcifications at the insertional tendon of rectus femoris and a continuous intramuscular oval mass lesion with central hypodensity of cystic content. There are peripheral discontinuous eggshell-like calcifications or circumferential peripheral calcifications separate from the underlying bone, as well as peripheral rim enhancement on the venous phase with no heterogeneous soft tissue enhancement.
In the bone window, the calcifications appear like an ossification of an osteoid matrix with a corticated wall.
Case Discussion
Based on the clinical history of the patient and multimodality radiological imaging findings, features are suggestive of myositis ossificans.
The condition of post-traumatic myositis ossificans passes through stages starting from the organising of granulation tissue formation and reaching to ossification of an osteoid matrix with central collagen fibrous tissue in which the calcifications start in the periphery with rim peripheral enhancement wand no visualised heterogenous enhanced tissue to consider sarcomatous soft tissue. The peripheral calcifications appeared faint by radiograph at 4 weeks duration, as shown in our case to become more obvious by radiograph with ossification at about 3 months after the onset of the initial formation of a lesion.
The ossification of the proximal rectus femoris tendon from the anterior inferior iliac spine and the proximal part of the rectus femoris muscle is caused either by chronic tendinopathy including calcific tendinitis or injury.
It's a cause of pain, some limitation of joint mobility, and additional complicated arthropathy.
Co-author: Dr Ahmed Elfakih (radiologist)
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