title: Diffusion-weighted imaging in extracranial head and neck schwannomas: A distinctive appearance.
abstract: OBJECTIVE
  To evaluate the diffusion weighted (DW) magnetic resonance imaging (MRI) features of the extracranial schwannomas of head and neck.
  
  
  METHODS
  The MRI (including DWI) of 12 patients with pathologically proven head and neck schwannomas (4 men, 8 women, with mean age of 32.6 years; age range 16-50 years) were retrospectively evaluated. Images were analyzed for signal intensity and morphology on conventional sequences followed by the qualitative evaluation of DW images (DWI) and measurement of apparent diffusion coefficient (ADC) values.
  
  
  RESULTS
  Majority of the tumors were located in the parapharyngeal space (8/12). All but one showed heterogeneous appearance, with 10 tumors showing scattered areas of hemorrhage. Eight out of 12 tumors showed intensely hyperintense core surrounded by intermediate signal intensity peripheral rim (reverse target sign) on T2-weighted (T2W) images. On DWI, these eight tumors showed a distinctive appearance, resembling target sign on trace DWI and reverse target on ADC map. Out of the remaining four tumors, one showed uniformly restricted diffusion whereas three showed free diffusion. Mean ADC value in the central area of free diffusion was 2.277 × 10(-3) mm(2)/s (range of 1.790 × 10 -(3) to 2.605 × 10(-3) mm(2)/s) whereas in the peripheral area was 1.117 × 10(-3) mm(2)/s (range of 0.656 × 10(-3) to 1.701 × 10(-3) mm(2)/s). Rest of the schwannomas showing free diffusion had a mean ADC value of 1.971 × 10(-3) mm(2)/s.
  
  
  CONCLUSIONS
  Majority of the head and neck schwannomas showed a characteristic appearance of free diffusion in the centre and restricted diffusion in the periphery of the mass.
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Abanti
authors.initials: A
authors.lastname: Das
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Ashu S
authors.initials: AS
authors.lastname: Bhalla
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Raju
authors.initials: R
authors.lastname: Sharma
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Atin
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Department of Otolaryngorhinology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Alok
authors.initials: A
authors.lastname: Thakar
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Ankur
authors.initials: A
authors.lastname: Goyal
keywords: Benign; diffusion weighted imaging; head and neck neoplasms; magnetic resonance imaging; schwannoma