title: MR imaging findings in transient osteoporosis of the hip.
abstract: OBJECTIVE
  The authors sought to describe the magnetic resonance (MR) imaging findings including perfusion imaging, in association with the course of acute bone marrow oedema syndrome (aBMEs), in a group of patients with acute hip pain and a final diagnosis of transient osteoporosis of the hip (TOH).
  
  
  METHODS
  From 217 patients referred with a probable diagnosis of avascular necrosis (AVN) of the femoral head, we identified 42 patients who had clinical and radiographic findings not relevant to AVN. MR imaging examinations were performed on a 1.0T scanner. Perfusion imaging was performed in 20 patients. The bone marrow oedema (BME) was classified in four stages. In addition, the presence or absence of oedema in the subchondral area and the presence of other subchondral lesions were recorded. Acetabular bone marrow was also assessed for the presence of oedema. The quantitative measurements included: maximum size of the effusion, percentage of enhancement (PE) and time of peak enhancement of abnormal marrow compared to the first pass, on the perfusion images.
  
  
  RESULTS
  Osteopenia was present on plain radiographs in 87% of cases. The most common pattern of BME was extending to the femoral head and neck. Acetabulum was involved in 16.6%. In 22.6% the BME spared the subchondral region of the femoral head. There were two cases (4.7%) with subchondral changes. A joint effusion was noted in 33 of the 42 patients. On perfusion imaging, a delayed peak enhancement was noted in 20 patients between 40 and 65 s after the first pass of contrast. No patient had any evidence of femoral head collapse or change in sphericity on follow-up MRI. None of the patients developed avascular necrosis in a time frame of 18 months from the onset of the acute hip pain.
  
  
  CONCLUSIONS
  The aBMEs MR imaging pattern varies and is most commonly appearing on X-rays as osteopenia. Absence of subcondral lesions, delayed peak enhancement of the abnormal marrow on perfusion images, and sparing of subchondral zone from marrow oedema are MR imaging findings highly correlated to TOH.
authors.affiliation: Department of Orthopaedic Surgery, School of Health Sciences, University of Thessaly, 22 Papakiriazi Street, Larissa 412 22, Greece. kmalizos@otenet.gr
authors.forename: Konstantinos N
authors.initials: KN
authors.lastname: Malizos
authors.forename: Aristidis H
authors.initials: AH
authors.lastname: Zibis
authors.forename: Zoe
authors.initials: Z
authors.lastname: Dailiana
authors.forename: Michael
authors.initials: M
authors.lastname: Hantes
authors.forename: Theophilos
authors.initials: T
authors.lastname: Karachalios
authors.forename: Theophilos
authors.initials: T
authors.lastname: Karahalios
authors.forename: Apostolos H
authors.initials: AH
authors.lastname: Karantanas
mesh_terms: D000328:Adult; D000368:Aged; D001855:Bone Marrow Diseases / Q000150:complications; D003937:Diagnosis, Differential; D004487:Edema / Q000150:complications; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging / Q000473:pathology; D005271:Femur Head Necrosis / Q000175:diagnosis; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010024:Osteoporosis / Q000175:diagnosis*; D010146:Pain / Q000209:etiology; D011859:Radiography; D013997:Time Factors