Deep gluteal syndrome (DGS) is an underdiagnosed entity characterized by pain and/or dysesthesias in the buttock area, hip or posterior thigh and/or radicular pain due to a non-discogenic sciatic nerve entrapment in the subgluteal space. Multiple pathologies have been incorporated in this all-included "piriformis syndrome," a term that has nothing to do with the presence of fibrous bands, obturator internus/gemellus syndrome, quadratus femoris/ischiofemoral pathology, hamstring conditions, gluteal disorders and orthopedic causes. The concept of fibrous bands playing a role in causing symptoms related to sciatic nerve mobility and entrapment represents a radical change in the current diagnosis of and therapeutic approach to DGS. The development of periarticular hip endoscopy has led to an understanding of the pathophysiological mechanisms underlying piriformis syndrome, which has supported its further classification. A broad spectrum of known pathologies may be located nonspecifically in the subgluteal space and can therefore also trigger DGS. These can be classified as traumatic, iatrogenic, inflammatory/infectious, vascular, gynecologic and tumors/pseudo-tumors. Because of the ever-increasing use of advanced magnetic resonance neurography (MRN) techniques and the excellent outcomes of the new endoscopic treatment, radiologists must be aware of the anatomy and pathologic conditions of this space. MR imaging is the diagnostic procedure of choice for assessing DGS and may substantially influence the management of these patients. The infiltration test not only has a high diagnostic but also a therapeutic value. This article describes the subgluteal space anatomy, reviews known and new etiologies of DGS, and assesses the role of the radiologist in the diagnosis, treatment and postoperative evaluation of sciatic nerve entrapments, with emphasis on MR imaging and endoscopic correlation.

The ligamentum teres has traditionally been viewed as an embryonic remnant with no role in the biomechanics or vascularity of adult hips. However, the ligamentum teres is a strong intraarticular ligament that is anatomically and biochemically similar to the anterior cruciate ligament of the knee. It is composed of two bands that originate from the acetabular transverse ligament and the pubic and ischial margins of the acetabular notch. Among other functions, the ligamentum teres is an important stabilizer of the hip, particularly in adduction, flexion, and external rotation. Abnormalities of the ligamentum teres account for 4%-15% of sports-related injuries and should be considered in the differential diagnosis of patients with hip pain. Lesions of the ligamentum teres include partial or complete traumatic tears, degenerative tears, avulsion fractures of the ligament at its insertion into the fovea capitis femoris, and a congenital absence of the ligament. Magnetic resonance arthrography and computed tomographic arthrography are the preferred modalities for precise preoperative diagnosis of ligamentum teres injuries and may be used to rule out other associated intraarticular injuries. Treatment of these lesions is still evolving; at present, treatment of most injuries is limited to arthroscopic débridement.

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A Fig. 1.-Diagram shows site and extent of anterolateral impingement lesion (arrow).