Case discussion
01Clinical context
A young adult presented with swelling and pain in the right thigh with no clear precipitating cause. Contrast-enhanced MRI of the thigh was performed to characterise the soft-tissue process.
02Key imaging findings
STIR images showed diffuse hyperintense oedema within the intramuscular and myofascial planes of the anterior and lateral compartments, predominantly the vastus lateralis and vastus intermedius, extending into the posterolateral deep subcutaneous plane. Post-contrast imaging demonstrated heterogeneous enhancement with patchy confluent peripheral (rim) enhancement surrounding non-enhancing central hypointensities; the largest, in the myofascial plane of the posterior vastus lateralis, measured 24 × 18 × 60 mm (≈13 cc), favouring a possible abscess on a background of myositis. The femur showed normal marrow signal with no fracture, stress response or bone oedema, and there was no sinus tract or calcification.
03Diagnostic reasoning
The reading began on STIR, which showed the oedema was compartment-wide across the anterior and lateral thigh and tracked along myofascial planes into the deep subcutaneous fat — a distribution typical of myositis rather than a discrete mass. The pivotal step was the post-contrast series: most of the involved muscle enhanced heterogeneously, consistent with inflammation, but discrete foci showed peripheral rim enhancement around a non-enhancing centre, the pattern of a liquefied/organising collection rather than solid tumour or simple oedema. The largest such focus in the posterior vastus lateralis was measured (24 × 18 × 60 mm, ≈13 cc) and reported as a possible abscess. Absence of a sinus tract, absence of calcification, and normal femoral marrow signal with no bone oedema were documented to argue against a draining infection and against contiguous osteomyelitis.
04Questions for clinical practice
Is this definitely an abscess? The report favours a *possible* abscess based on the rim-enhancing, centrally non-enhancing focus; correlation with clinical picture and inflammatory markers, and aspiration if indicated, would confirm it. Does the femur being normal matter? Yes — normal marrow signal with no bone oedema argues against contiguous osteomyelitis, which changes the treatment duration and approach. What does the measured volume add? The 24 × 18 × 60 mm (≈13 cc) collection and its exact location give the referring team a concrete target should image-guided drainage be considered rather than antibiotics alone.
05Teaching point
In a painful, swollen limb, STIR maps the extent of myofascial and intramuscular oedema, but it is the post-contrast pattern that discriminates: diffuse heterogeneous enhancement supports myositis, while a rim-enhancing focus with a non-enhancing centre raises an organising abscess. Reporting the discriminating pattern, the exact site and the measured volume gives the clinician what is needed to decide between antibiotics alone and drainage, and a normal femoral marrow reassuringly argues against contiguous osteomyelitis.
Shown for education. De-identified — no identifiable patient data. A radiology report is a specialist opinion and must be read with the full clinical context by the treating physician.