title: Understanding the natural history of focal nodular hyperplasia in the liver with MRI.
abstract: OBJECTIVE
  To determine the incidence of natural growth or regression of focal nodular hyperplasia (FNH) in the liver.
  
  
  METHODS
  We retrospectively included 120 consecutive patients who were diagnosed to have FNH on MRI. The mean follow-up duration was 19 months (range: 6-64 months). There were 25 men and 95 women (age range: 18-80 years; mean: 45 years). There were 167 FNH lesions in the 120 patients. MRI images were retrospectively reviewed for interval growth or regression of FNH. The maximum size of the lesions was measured on axial arterial-phase images of the initial and the last MRI examinations. An interval increase or decrease in diameter of over 10% of the initial diameter was considered as positive growth or regression, respectively. The use of Oral contraceptives was also documented.
  
  
  RESULTS
  Interval growth was seen in 25/167 nodules (15%) over 7-48 months (mean: 21 months), with increase in size of 0.2-1.7 cm (mean: 0.6 cm) and percentage change of 10.5-340% (mean: 64%). Interval regression was seen in 13/167 (8%) of nodules over 7-63 months (mean: 22 months), with decrease in size of 0.2-0.9 cm (mean: 0.5 cm) and percentage change of 10.4-60% (mean: 24%).Five of 17 (29%) female patients with growing FNH and 25/78 (32%) female patients with non-growing FNH had a history of intake of oral contraceptives (P=0.83).
  
  
  CONCLUSIONS
  Although FNH is benign and of no clinical significance, a substantial percentage of FNH shows interval growth or regression on long-term follow-up with MRI.
authors.affiliation: Department of Medical Imaging, University Health Network, Mount Sinai Hospital and Women's College Hospital, University of Toronto, Toronto, ON, Canada.
authors.forename: Jaydeep A
authors.initials: JA
authors.lastname: Halankar
authors.forename: Tae Kyoung
authors.initials: TK
authors.lastname: Kim
authors.forename: Hyun-Jung
authors.initials: HJ
authors.lastname: Jang
authors.forename: Korosh
authors.initials: K
authors.lastname: Khalili
authors.forename: Haider A
authors.initials: HA
authors.lastname: Masoom