title: Imaging and histopathological evaluation of a cystlike formation in subchondral insufficiency fracture of the femoral head: A case report and literature review.
abstract: BACKGROUND
  In the majority of subchondral insufficiency fractures (SIFs) of the femoral head, T1-weighted magnetic resonance imaging shows an irregular, serpiginous, low-intensity band that is convex to the articular surface. We report a case of a cystlike formation in SIF of the femoral head in an elderly woman.
  
  
  METHODS
  A 71-year-old woman reported right hip pain without any history of antecedent trauma. The initial radiograph showed a slight narrowing of the joint space in the right hip. The patient was treated with conservative therapy for 2 months. Radiographs obtained 3 months after the onset of pain showed non-progressive joint-space narrowing. T1-weighted magnetic resonance images obtained 2 months after pain onset revealed a round, cystlike, low-intensity area just beneath the articular cartilage. The patient underwent total hip arthroplasty. Histopathological examination showed fracture callus and granulation tissue in the subchondral area, surrounded by vascular-rich granulation tissue and fibrous tissue, which corresponded to the round, low-intensity band observed on the T1-weighted image.
  
  
  CONCLUSIONS
  This case was a rare SIF of the femoral head which had a cystlike formation with a low signal intensity on T1-weighted images and a very high signal intensity on STIR sequences in the superolateral portion of the femoral head, surrounded by a pattern of edema in the bone marrow. To our knowledge, no similar cases were cited in the literature.
  
  
  CONCLUSIONS
  It is important for surgeons to keep in mind that sometimes SIFs of the femoral head can appear as a round cystlike formation.
authors.affiliation: Department of Orthopaedic Surgery, Kanazawa Medical University, Kahokugun, Japan. Electronic address: 66406kf@kanazawa-med.ac.jp.
authors.forename: Kiyokazu
authors.initials: K
authors.lastname: Fukui
authors.affiliation: Department of Orthopaedic Surgery, Kanazawa Medical University, Kahokugun, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Kaneuji
authors.affiliation: Department of Pathology and Medical Laboratory, Kanazawa Medical University, Kahokugun, Japan.
authors.forename: Mana
authors.initials: M
authors.lastname: Fukushima
authors.affiliation: Department of Orthopaedic Surgery, Kanazawa Medical University, Kahokugun, Japan.
authors.forename: Tadami
authors.initials: T
authors.lastname: Matsumoto
keywords: Femoral head; Histopathology; Subchondral insufficiency fracture