This case series from a hospital presents 5 cases of transient global amnesia (TGA) that were investigated with MRI. MRI findings of small punctate lesions in the hippocampus on diffusion-weighted imaging (DWI) supported the clinical diagnosis of TGA in all 5 cases. Previous studies have found hippocampal DWI lesions in 45-84% of TGA cases depending on timing of MRI and acquisition parameters like slice thickness and diffusion weighting. Improved MRI techniques allow for detection of subtle lesions that correlate with the pathophysiology of selective hippocampal vulnerability in TGA.

2.  Self-limiting antegrade amnesia
› In absence of other causes

3.  Witnessed
 Antegrade amnesia
› Unable to form new memories
› Perserveration
 “Broken record”
› Sometimes also retrograde
 No other cognitive impairment or altered consciousness
› Otherwise, alert and well
 Duration of episode resolves within 24hrs
› 1-10 hrs, average 6hrs
 No other neurological deficit/epileptic features/head trauma
› Diagnoses of exclusion
 Precipitating event

4.  No concensus
 Theories include:
› Vascular dysfunction
 Arterial or Venous
› Paroxysmal neuronal discharge/Epileptic phenomena
 Self propagating wave of neuronal depolarisation

5.  Nothing
› Self resolving

6.  Exclude other causes
› Diagnosis
 treatment
› Prognosis

7. DDx Clinical Findings MRI findings
Transient epileptic
amnesia
<1hr, multiple
attacks at time of
presentation
Increased T2/FLAIR in
hippocampus, thalamus and
cortex
TIA/CVA Amnesia in absence
of other focal
neurodeficits rare
DWI in vascular territories
Wernickes
encephalopathy
More global
amnesia and
inattention
Symmetrical increased T2/FLAIR
in mammillary bodies, medial
thalami, tectal plate and
periaqueductal area
tectal region (white arrows), periaqueductal area
(black arrowheads), and mamillary bodies (white
arrowheads
TGA Antegrade amnesia
<24hrs
DWI punctate (1-3mm) foci in
hippocampus, uni/bilateral
DDx
Transient epileptic
amnesia
TIA/CVA
Wernickes
encephalopathy
TGA

8.  Fn
› Involved in learning & memory
 Part of mesial temporal lobe
› Below temporal horn of lateral ventricles
› Seahorse
› Made up of dentate gyrus, C1-4.

9.  Blood supply:
› PCA
 hippocampal arteries
› AChA
 Branch of ICA

10.  5 TGA cases presented to the Calvary Hospital
› Between March 2013 to February 2015
 All had MRI findings typical of TGA

11.  61 yo male
 No significant PMHx
 Acute confusion and amnesia
› Repetitive questioning
 Alert
 Ix:
› CTB: NAD
› LP: NAD

12.  Day 1 MRI
 2 punctate DWI lesions in left hippocampus

13.  66yo male
 PMHx: T2 DM, hypertension and hypercholesterolaemia
 Acute onset of amnesia and confusion
 Alert
 Repetitive questioning
 CTB: NAD

14.  Day 1 MRI
 Punctate DWI lesion in left hippocampus

15.  62yo female
 PMHx: Meniere’s disease, migraine and hypertension
 Sudden onset of anterograde and retrograde amnesia
 Nausea and vomiting, worse than usual Meniere’s
 Alert
 CTB: NAD

16.  Day 2 MRI
 5mm DWI hyperintense focus in the left hippocampus

17.  63yo female
 Sudden onset confusion and amnesia at work
 PMHx: NAD
 Alert
› No memory of days events
 CTB: NAD

18.  Day 2 MRI
 4.5mm DWI hyperintense focus in the left hippocampus

19.  64yo female
 PMHx: OA
 Amnesic events at the gym and whilst doing errands

20.  Day 2 MRI
 5mm DWI lesion in left hippocampus

21.  Left hippocampal DWI lesion

22.  81yo female
 PMHx: AF, AV replacement
 Acute confusion and dysphasia
› Resolved next day
 Acute left hippocampal infarction

23.  Left hippocampal DWI focus

24.  78yo male
 PMHx: EtOH, COPD
 Recurrent episodes of decreased levels of
consciousness
› Staring and not responding
› Over last few months
› Lasts 10mins
 Followed by 2-3 hrs of fatigue
 Complex partial seizures

25.  Cases demonstrating DWI focus in hippocampus
› BUT not TGA clinically

26. Hippocampal DWI Lesions ≠ TGA

27.  Total 99 patients
› 52 had DWI changes
 45 in hippocampal region
 25 left, 9 bilateral, 11 right
› Sedlaczek et al.
 26 out of 31 had punctate hippocampal
DWI lesions
 All 5 TGA cases showed hippocampal DWI lesion
Sander&Sander,LancetNeuro.2005

28.  Small case series
 Reflective of literature
 Diagnosis to consider
 Review area
 Clinical diagnosis
“Clinical correlation is recommended”

29.  Dr Yash Gawarikar
 Dr Alexander Lam
 Dr Brett Jones
 Dr Yun Tae Hwang

34.  Consistent with other studies
 MRI findings supports clinical diagnosis
› Treatment and prognosis
 100% MRI detection rate
› Why?
 Optimised protocol
 t = 24-72 hrs
 b = 2000
 3mm thick slices

37. Previously brain imaging normal
Now…
Improvements in MRI:
 Small punctate (1-3mm) DWI hyperintense foci in lateral
hippocampus (CA1 sector of hippocampus)
 Often Unilateral and left sided
› Selective vulnerability of this region to metabolic stressors
 glutamate excitotoxicity and Ca2+ influx

38.  MR-spectroscopy of hippocampal DWI lesion
› Lactate peak  further evidence for CA1 neuronal dysfuction
 No abnormality in vessels on MRA
 Dy/dx with Wernicke encephalopathy
 DWI in medial thalami, mammillary bodies,
periaqueductal region, tectal plate

39.  Frequency of detection 0-84%
› Large range!
› Likely related to timing of MRI from onset of symptoms
› Sedlaczek (2004) - 6% detection rate when Mri done within 8 hrs of onset
› Increased to 84% at 48hrs post onset
 B values >1000
› Weon (2008) – detection rate @ B= 1000 (3mm thickness) was 38%, @ B=2000 (3mm
thickness) was 54%. No difference between B=2000 and B=3000.
 As B value increases  diffusion weighting increases  increases detection
 Slice thickness <5mm
› Weon- detection rate within 24 hrs @5mm thickness – 13%, then increased to 38% at 3mm
 Increase detection of small punctate lesions by decreasing partial volume
averaging effects

40.  Ahn – overall time to MRI was 6hrs . However, those with MRI
changes is 9 hrs
 16 out of 203 TGA over 7yrs with DWI hippocampal changes
 Bartsch – found that lesions localised to CA1 of
hippocampus in 29 TGA patients in 24-72 hrs
 Peak incidence at 12-72hrs
 DWI normalisation on Day 10
 Similar to time course of ischaemic
  careful timing to find abnormalities
 Lesions resolve on F/U imaging in 1-6 months

41.  3T magnet
 Acquisition between 24 to 72 hours
 3mm DWI slice thickness
 Detection increased 88% when scan performed 2-3
days post event, DWI with resolution B=2000, slice
thickness 2-3mm.