Case discussion
01Clinical context
A patient presents with localized left buttock pain along the course of the sciatic nerve. MRI of the pelvis was performed without intravenous contrast to evaluate the cause of pain.
02Key imaging findings
MRI shows prominent subchondral marrow edema on both sides of the left sacroiliac joint with trace joint effusion and minimal articular surface irregularity. Mild adjacent inflammatory soft-tissue edema is present anterior to the joint. The right sacroiliac joint is normal. No significant abnormalities in the hips or gluteal muscles and tendons are seen.
03Diagnostic reasoning
The diagnosis was established by identifying subchondral marrow edema on fluid-sensitive sequences centered on the left sacroiliac joint, accompanied by trace joint effusion and mild adjacent soft-tissue inflammatory changes. The absence of abscess or drainable collections was confirmed. The right sacroiliac joint and hips were evaluated and found normal, excluding bilateral involvement or alternative causes of pain.
04Questions for clinical practice
What is the likely cause of the active sacroiliitis? The report suggests clinical and laboratory correlation to differentiate inflammatory from infectious causes. How should the patient be managed? Management depends on the underlying etiology determined clinically. When should follow-up imaging be considered? Follow-up MRI may be warranted if symptoms persist or worsen despite treatment to assess response or progression.
05Teaching point
Active sacroiliitis can be identified on MRI by subchondral marrow edema, joint effusion, and adjacent soft-tissue inflammation. Recognizing these features is essential for diagnosing inflammatory causes of buttock pain and guiding further clinical and laboratory evaluation.
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.