The presacral space is a clinically important space that is relevant to multiple disciplines and lies at the intersection of the axial skeleton, neural axis, and pelvic soft tissues. A wide variety of benign and malignant conditions may derive from its various elements. An appropriate differential diagnosis may be formulated from a more comprehensive list by considering the specific imaging features of a given case: In particular, involvement of the sacrum (either remodeling or destruction) and the presence or absence of a solid, soft-tissue component may help narrow the differential diagnosis. Typically, osteochondral and neurogenic tumors remodel or destroy the sacrum, whereas sacral involvement is less common in patients with a mesenchymal tumor. Ewing sarcomas and chordomas are typically associated with a large soft-tissue mass. Demographic features are also important: Typically, congenital and developmental tumors occur in younger patients, and chondrosarcomas occur in older patients (mean age, 45 years). Finally, specific imaging features may help establish the diagnosis. For instance, an osseous or chondroid matrix is indicative of osteosarcoma or chondrosarcomas; neurofibromas may have a target appearance at magnetic resonance (MR) imaging; hemangiomas have areas of increased signal intensity on T1-weighted MR images, a result of fat and hemorrhage; and myeloplipomas contain macroscopic fat.

Background: Iliopsoas tenotomy is a treatment for snapping hip. Does this surgical procedure change the surrounding muscle and tendon anatomy? Questions/ Purposes: This study seeks to evaluate the changes in the MR appearance of the hip muscles and iliopsoas tendon in patients following arthroscopic iliopsoas tenotomy. Methods: One hundred sixty-nine consecutive adults were evaluated after iliopsoas tenotomy at the lesser trochanter. Each MR exam was evaluated independently by three radiologists for muscle edema, atrophy (grade 0-4), compensatory hypertrophy, signal within the iliopsoas tendon (increased on T1 or T2 sequences), and iliopsoas tendon morphology (distorted or disrupted) above, at, and below the iliopectineal eminence. A finding was considered positive if reported by two or three of the radiologists. Results: Twenty subjects met the inclusion criteria. Muscle edema was present in 15% (3/20) of subjects within the iliacus, psoas, and quadratus femoris. The majority of postoperative symptomatic patients has atrophy of the iliacus and psoas muscles and distortion and disruption of the iliopsoas tendon and should be recognized as a normal imaging appearance following iliopsoas tendon release.

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