title: Normal fetal posterior fossa in MR imaging: new biometric data and possible clinical significance.
abstract: OBJECTIVE
  Posterior fossa malformations are a common finding in prenatal diagnosis. The objectives of this study are to re-evaluate existing normal MR imaging biometric data of the fetal posterior fossa, suggest and evaluate new parameters, and demonstrate the possible clinical applications of these data.
  
  
  METHODS
  This was a retrospective review of 215 fetal MR imaging examinations with normal findings and 5 examinations of fetuses with a suspected pathologic posterior fossa. Six previously reported parameters and 8 new parameters were measured. Three new parameter ratios were calculated. Interobserver agreement was calculated by using the intraclass correlation coefficient.
  
  
  RESULTS
  For measuring each structure, 151-211 MR imaging examinations were selected, resulting in a normal biometry curve according to gestational age for each parameter. Analysis of the ratio parameters showed that vermian lobe ratio and cerebellar hemisphere ratio remain constant with gestational age and that the vermis-to-cisterna magna ratio varies with gestational age. Measurements of the 5 pathologic fetuses are presented on the normal curves. Interobserver agreement was excellent, with the intraclass correlation coefficients of most parameters above 0.9 and only 2 parameters below 0.8.
  
  
  CONCLUSIONS
  The biometry curves derived from new and existing biometric data and presented in this study may expand and deepen the biometry we use today, while keeping it simple and repeatable. By applying these extensive biometric data on suspected abnormal cases, diagnoses may be confirmed, better classified, or completely altered.
authors: From the Departments of Obstetrics and Gynecology (R.B., D.S., R.A., E.K.) berlerner@gmail.com.
authors: R
authors: R
authors: Ber
authors: Pediatric Neurology (O.B.-Y.).
authors: O
authors: O
authors: Bar-Yosef
authors: Diagnostic Imaging (C.H.), Chaim Sheba Medical Center, Tel Hashomer, Tel-Aviv University, Tel-Aviv, Israel.
authors: C
authors: C
authors: Hoffmann
authors: From the Departments of Obstetrics and Gynecology (R.B., D.S., R.A., E.K.).
authors: D
authors: D
authors: Shashar
authors: From the Departments of Obstetrics and Gynecology (R.B., D.S., R.A., E.K.).
authors: R
authors: R
authors: Achiron
authors: From the Departments of Obstetrics and Gynecology (R.B., D.S., R.A., E.K.).
authors: E
authors: E
authors: Katorza
mesh_terms: D001699:Biometry; D001921:Brain / Q000002:abnormalities*; D005260:Female; D005333:Fetus / Q000002:abnormalities*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal
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