title: "Invisible" brain stem infarction at the first day.
abstract: BACKGROUND
  In specific stroke cases, serial diffusion-weighted magnetic resonance imaging (DW MRI) on day 1 was unable to show a lesion, whereas that on day 4 and later clearly revealed a lesion. However, clinical features of this phenomenon ("invisible" brain stem infarction [IBI] at the first day) have not been fully delineated.
  
  
  METHODS
  We retrospectively recruited 212 stroke patients in the Emergency Unit and Neurology Department. Among these, we studied patients with IBI. Definition of IBI is that acute and clear brain stem symptoms/signs on arrival were ameliorated at discharge and appearance of high signal intensity on serial DW images with low apparent diffusion coefficient (ADC) by 1.5 T MRI with 2-mm slices.
  
  
  RESULTS
  IBI were found in only 6 patients. Day 1 invisible stroke was found only in the brain stem (17%, 6 of 35) but none (0 of 177) in the hemispheric infarction (P < .05). In most patients with IBI, DW MRI turned out visible at the third/fourth day. Before the fourth day, DW/ADC signal changes in patients with IBI were minimal. In IBI, lesion size (mean 2.7 mm(2)) was smaller than that of visible cases (mean 7.3 mm(2)). In IBI, lesion location was mostly at the dorsolateral medulla. In IBI, sensory disturbance was significantly more common (67%) than visible cases (24%; P < .05), whereas dysarthria was less common (0%; P < .01) than visible cases (66%; P < .01).
  
  
  CONCLUSIONS
  It is likely that patients with smaller stroke volume, sensory disturbance, and medullary location are prone to develop IBI. When evaluating stroke using MRI criteria, recognition of IBI is important to start early management.
authors.affiliation: Department of Neurology, Internal Medicine, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Tsuyusaki
authors.affiliation: Department of Neurology, Internal Medicine, Sakura Medical Center, Toho University, Sakura, Japan. Electronic address: sakakibara@sakura.med.toho-u.ac.jp.
authors.forename: Ryuji
authors.initials: R
authors.lastname: Sakakibara
authors.affiliation: Department of Neurology, Internal Medicine, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Kishi
authors.affiliation: Department of Neurology, Internal Medicine, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Fuyuki
authors.initials: F
authors.lastname: Tateno
authors.affiliation: Department of Neurology, Internal Medicine, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Aiba
authors.affiliation: Department of Neurology, Internal Medicine, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Ogata
authors.affiliation: Department of Neurosurgery, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Takeki
authors.initials: T
authors.lastname: Nagao
authors.affiliation: Department of Radiology, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Terada
authors.affiliation: Department of Radiology, Sakura Medical Center, Toho University, Sakura, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Inaoka
mesh_terms: D000208:Acute Disease; D000368:Aged; D000369:Aged, 80 and over; D020526:Brain Stem Infarctions / Q000473:pathology*; D038524:Diffusion Magnetic Resonance Imaging; D004632:Emergency Medical Services; D005260:Female; D006801:Humans; D008297:Male; D008526:Medulla Oblongata / Q000473:pathology; D008875:Middle Aged; D009422:Nervous System Diseases / Q000175:diagnosis / Q000209:etiology; D012189:Retrospective Studies; D020521:Stroke / Q000209:etiology / Q000473:pathology
keywords: Stroke; brain stem; diffusion-weighted image; magnetic resonance imaging