1. Transient Global Amnesia
MRI Case Series
Dr Lan Nguyen (Radiology Registrar)
Dr Tarun Jain (Consultant Radiologist)

2. What is Transient Global Amnesia (TGA)?
Self-limiting antegrade amnesia
In absence of other causes
Constellation of symptoms

3. Clinical Symptoms 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
Perserveration = Repetitive questioning
In bold is are the Caplan and Hodges diagnostic criteria
??Diagnosis of exclusion

4. Pathophysiology No concensus Theories include: Vascular dysfunction
Arterial or Venous
Paroxysmal neuronal discharge/Epileptic phenomena
Self propagating wave of neuronal depolarisation
Ischaemia or venous congestion
Abnormal firing of neurones

5. Treatment
Nothing
Self resolving

6. Role of Imaging Exclude other causes Diagnosis  treatment Prognosis
So if we do nothing for TGA, why is imaging important?
Because TGA more of a diagnoses of exclusion, imaging is used to diagnose/exclude other causes of amnesia

7. Differentials 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
The other causes of amnesia include
Clinical and Mri findings are different in terms of distribution of signal.

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

9. Hippocampus Continue Blood supply: PCA AChA hippocampal arteries
Branch of ICA
Hippocampus vulnerable to ischemia.
As hippocampal artery supplies an internal anastomosis forming a link between an upper and a lower artery  watershed area = “hypoxia-susceptible sector of Sommer”
Hippocampus vulnerable to excitotoxic mechanisms.
Stressful events  overexcite hippocampus  glutamate release  triggers spreading depression and the functional ablation of the hippocampus

10. Cases 5 TGA cases presented to the Calvary Hospital
Between March 2013 to February 2015
All had MRI findings typical of TGA
5 clinically diagnosed cases of TGA presented to Calvary hospital between
All had similar findings on MRI, which I will present to you.

11. Case 1 - WQ 61 yo male No significant PMHx Acute confusion and amnesia
Repetitive questioning
Alert
Ix:
CTB: NAD
LP: NAD

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

13. Case 2 - NY
66yo male
PMHx: T2 DM, hypertension and hypercholesterolaemia
Acute onset of amnesia and confusion
Alert
Repetitive questioning
CTB: NAD

14. Case 2 - MRI
Day 1 MRI
Punctate DWI lesion in left hippocampus

15. Case 3 - JT
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. Case 3 - MRI
Day 2 MRI
5mm DWI hyperintense focus in the left hippocampus

17. Case 4 - SZ 63yo female Sudden onset confusion and amnesia at work
PMHx: NAD
Alert
No memory of days events
CTB: NAD

18. Case 4 - MRI
Day 2 MRI
4.5mm DWI hyperintense focus in the left hippocampus

19. Case 5 - ED 64yo female PMHx: OA
Amnesic events at the gym and whilst doing errands

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

21. Case 6 - MRI
Left hippocampal DWI lesion

22. Case 6 - MM 81yo female PMHx: AF, AV replacement
Acute confusion and dysphasia
Resolved next day
Acute left hippocampal infarction

23. Case 7 - MRI
Left hippocampal DWI focus

24. Case 7 - KC 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. Hippocampal DWI Lesions
Cases demonstrating DWI focus in hippocampus
BUT not TGA clinically
During this period there were DWI hippocampal lesions, that were clinically NOT TGA

26. Hippocampal DWI Lesions ≠ TGA
These last 2 cases were to demonstrate that not all hippocampal DWI lesions are TGA
Clinical ___ important

27. Other Studies 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, Lancet Neuro. 2005
Our small case series of 5 patients, how does this compare with other studies?
Sander and Sander collated case reports and case series , with a combined total of 99 patients.
52 had DWI changes , of which 45 were located hippocampus.
Reason why some studies had no MRI changes:
timing. TGA usual present by hr
DWI abnormalities highly sensitive for ischaemia but not specific

28. Limitations / Implications
Small case series
Reflective of literature
Diagnosis to consider
Review area
Clinical diagnosis
“Clinical correlation is recommended”
Now that we know what is out there in the literature, we need to be mindful of the implications and limitations of our case series
We do have a small sample size, however our findings are reflective of the literature as discussed prior.
In radiology, TGA is a diagnosis to keep in mind.
And we know that the high yield review area is in the hippocampus.
However, ultimately TGA is a clinical diagnosis – and that clinical correlation is recommended.

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

30. Thanks!

34. Our Case Series Consistent with other studies
MRI findings supports clinical diagnosis
Treatment and prognosis
100% MRI detection rate
Why?
Optimised protocol
t = hrs
b = 2000
3mm thick slices
Our small casse series is Increases detection rates

37. Imaging 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 B= 1000 (3mm thickness) was 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 thickness – 13%, then increased to 38% at 3mm
Increase detection of small punctate lesions by decreasing partial volume averaging effects

40. Timing of MRI
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 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. MRI Imaging protocol in TGA
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.
Can this protocol pick up all the DDx??
Since TGA is diagnosis of exclusion, this protocol is able to exclude other DDx…
Increase sensitivity /detection rate