MR imaging of the ischiopubic synchondrosis A.M. Herneth a, *, S. Trattnig a , T.R. Bader a , A. Ba-Ssalamah a , W. Ponhold a , K. Wandl-Vergesslich b , L.S. Steinbach c a Department of Radiology, AKH - 7F, University of Vienna, Austria Wahringer Gurtel 18 –20 A–1090 Wien, Austria b Department of Pediatrics, University of Vienna, Austria Wahringer Gurtel 18 –20 A–1090 Wien, Austria c Department of Radiology, University of California San Francisco 505 Parnassus, Room M-392 San Francisco, CA 94143, USA Received 14 December 1999; accepted 12 February 2000 Abstract The ischiopubic synchondrosis (IPS) is a temporary joint, occurring in childhood prior to fusion of the ischial and pubic bones. On conventional radiographs this tumor-like appearance is a well known normal anatomic variant, however, there are no reports in the literature of the appearance of IPS on MRI. Therefore the purpose of this study was to evaluate typical magnetic resonance features of the IPS. All pelvic MRIs from 1/1992 to 4/1998 of children ranging in age from 4 to 16 years, who were scanned for reasons other than bone disorders, were retrospectively investigated. Twenty-eight children were included and the morphologic appearance of IPS on MRI was evaluated. Seventeen (61%) of these 28 children had the following findings of IPS on MRI. Listed in order of frequency we found signal alteration of the ischiopubic fusion zone [hyperintense on T 2 with fat-saturation (89%) or STIR (74%), hypointense on T 1 (71%)], fibrous “bridging” (68%) [hypointense band on all sequences in perpendicular orientation to the axis of the inferior pubic ramus], fusiform swelling (68%), signal alteration of the adjacent soft tissue (57%) and irregular margins (56%). In 10 children contrast enhanced scans were available for evaluation, showing contrast enhancement of the bone marrow in 83.3% and of the adjacent soft tissue in 66.7%. Fusiform swelling of the ischiopubic fusion zone, signal alteration and contrast enhancement of both the bone marrow and the adjacent soft-tissue are characteristic features of the IPS on MRI, which may be due to mechanical stress at this temporary joint. These features are nonspecific and may resemble tumor, infection or trauma. Fibrous “bridging” was the only finding on MRI, which has not been described for any other entity and thus, it seems to be a characteristic MRI-feature. © 2000 Elsevier Science Inc. All rights reserved. Keywords: Pelvis; MRI; Normal variant; Children; Musculo-skeletal 1. Introduction Synchondroses are temporary joints that exist almost uniquely during skeletal maturation and are composed of hyaline cartilage [1]. With skeletal maturation, synchondro- ses become thinner and usually obliterate by bony union or synostosis. The time of closure is somewhat variable, but typically begins in early childhood and is completed before puberty [2,3]. The IPS, which is considered to be a normal variant, can frequently be seen on conventional radiographs, where it appears as a tumor-like fusiform radiolucent area at the ischiopubic fusion zone [1]. Despite of its typical appear- ance the IPS can resemble neoplasia, post-traumatic osteol- ysis, osteomyelitis and a stress fracture leading to continu- ous reports in the literature of problems in the differential diagnosis, which then may lead to invasive and extensive work-up [1,4,7,8]. The clinical appearance of the IPS is nonspecific and does not help in the differential diagnosis of equivocal findings on conventional radiographs. In general the fusion of the ischial and the pubic bones causes no symptoms, whereas in some children it is accompanied by pain in the groin and restriction in the movement of the hip joint [1,4 – 6]. Because neoplasia and osteomyelitis may be present without causing symptoms, equivocal findings of the IPS on conventional radiographs may cause problems in the differ- ential diagnosis in both symptomatic and asymptomatic children [9]. Other diagnostic tools such as computed tomography (CT), scintigraphy, or laboratory tests are nonspecific and are not helpful in the differential diagnosis of this tumor- * Corresponding author. Tel.: +43-1-40400-7620; fax: +43-1-40400- 4898. E-mail address: andreas.herneth@univie.ac.at (A. Herneth). Magnetic Resonance Imaging 18 (2000) 519 –524 0730-725X/00/$ – see front matter © 2000 Elsevier Science Inc. All rights reserved. PII: S0730-725X(00)00138-7