Abstract

A 64-year-old gentleman, presented for subacute onset of short-term memory problem, preceded by headache, right arm numbness and visual disturbances. On neurological exam, he had anterograde amnesia, decreased pinprick sensation on his right arm and right homonymous hemianopsia.

Brain Magnetic Resonance imaging (MRI) and Magnetic Resonance Angiography (MRA) showed subacute ischemic lesions in the left occipital lobe, hippocampus and thalamus, caused by a distal occlusion of the left Posterior Cerebral Artery (PCA). A distal occlusion of the PCA led to multiple infarcts in different anatomical structures, causing a constellation of variant neurological signs.

Our case demonstrates an anterior hippocampus predominantly irrigated by the PCA.

Background

The Hippocampus is mainly supplied by the PCA and to a lesser degree from the anterior choroidal artery.^[2] Visual analysis with Diffusion-Weighted MRI (DWI) have identified 4 patterns of lesions affecting the hippocampus: complete, lateral, dorsal and circumscribed lesions in the lateral hippocampus.^[3] The PCA strokes are associated with headaches, visual symptoms, sensory-motor symptoms and neuropsychological symptoms^[5] headaches being the initial and most frequently seen manifestation of infarcts in the posterior rather than the anterior circulation.^[6] Other associated symptoms of posterior strokes include dizziness, confusion, nausea and vomiting.^[5] When the involved region is limited to the hippocampal area, amnesia and memory processing are mainly affected.^[3] This amnesia is usually temporarily, not lasting more than 24 hours, and it is called Transient Global Amnesia (TGA).^[7]

The prevalence of an isolated acute stroke of the hippocampus is 0.03% in a case series of 6800 patients.^[8] Ischemic lesions are well identified on DWI due to strong contrast between affected and unaffected tissues, which offers more details in stroke syndromes.^[4] The isolated involvement of the hippocampal structures enlighten its important role for memory processing.^[9] Transient Global Amnesia TGA is characterized by a transient anterograde or retrograde amnesia without decrease level of consciousness or any other cognitive disturbances.^[7] The patient usually shows a stereotyped behavior like repetitive questioning, due to short term memory impairment.^[10] Transient Global Amnesia TGA rarely present post an ischemic stroke, and it is reported with lesions on the unilateral or bilateral hippocampus.^[10,11] 

In the case discussed below, we present a patient with multiple comorbidities, presenting to the emergency with solely confusion and retrograde amnesia, that later on turned to be caused by stroke in the posterior cerebral artery; a very rare case presentation that needs to be addressed so emergency physicians and other care givers don’t miss out this diagnosis.

Case Presentation

     A 64-year-old male patient presented to the Emergency Department (ED) for altered general status mainly manifested by confusion, distress, and a high blood pressure. The patient is known to have hypertension, diabetes, dyslipidemia, with reported compliance to medical treatment, along with coronary artery disease, status post stent insertion in 2011.

In the Emergency Room, patient had severe headache, and a tingling sensation in his right arm involving the fingers; he denied any chest pain, dyspnea, orthopnea, fever or chills; he also denied any blurry vision or dipoplia, loss of consciousness, vertigo or dizziness. However, the patient’ family reported difficulty in arousing the patient from sleep during the morning of that same day with a retrograde amnesia of 30 minutes duration.

Vital signs were as follow: heart rate: 78 BPM, blood pressure: of 190/100 mmHg, temperature: 36.7^oC and oxygen saturation: 98% on room air. On review of system patient had no recent complaints or any signs of infection.

On physical exam, the patient was oriented to people and place but not to time, and he was not able to recall the events of the day prior to his presentation. Systolic ejection murmur radiating to the right carotids was heard on heart auscultation.

Neurologic exam showed intact Cranial Nerves (CN) III to XII, normal motricity in all limbs, positive pupillary light reflex, +2 DTR deep tendon reflexes and an equivocal Babinski on the right. There was decreased pinprick sensation on his right arm. On eye exam, the patient had a right homonymous hemianopsia.

The rest of the bed side exam was normal.

Stroke protocol was initiated, and brain MRI and MRA showed multiple areas of cortical ischemic lesions in the left occipital lobe, left hippocampus and left thalamus, which corresponds to subacute ischemic lesions in the territory of the left PCA (Figure 1).

The patient was immediately started on dual antiplatelet and anticoagulation and admitted to regular floor. During his stay, his home medications were continued and he was being followed by neurologic exam daily until discharge. Marked improvement was noticed at 1 month follow up in outpatient clinic with return to baseline in cognition.

 Discussion

     A 64-year-old gentleman, with uncontrolled hypertension and diabetes mellitus, presented for subacute onset of short-term memory problem, preceded by right arm numbness and visual disturbances. On neurological exam, he had anterograde amnesia reported by family that lasted less than 1 hour, decreased pinprick sensation on his right arm and right homonymous hemianopsia.

     Two thirds of the hippocampus are vascularized by the P2 segment of the PCA and the rostral third is generally irrigated by segments of the anterior choroidal arteries ^[3]. A stroke to the PCA will therefore affect cognitive and memory function; the majority will show verbal long term memory deficit ^[12], and the duration of amnesia is usually at least 10 hours to few months ^[13]. However, the patient in this case discussion, had short term memory impairment, no verbal deficit, and the duration was very short. Also, in the literature, the TGA related to hippocampal infarcts was also associated with infarcts in other vasculature territories such as middle cerebral artery and internal carotid artery ^[14], and hence no direct causation between TGA and PCA strokes solely can be made. TGA as a symptom, can be caused by several triggers such as sexual intercourse, anxiety, head trauma, emotional distress…but no vascular triggers identified in the literature, symptoms last for an average of 6 hours ^[15].
     In this case, brain MRI and MRA, showed subacute ischemic lesions in the left occipital lobe, hippocampus and thalamus (Figure1), caused by a distal occlusion of the left PCA (Figure 2). A distal occlusion of the PCA led to multiple infarcts in different anatomical structures, causing a constellation of variant neurological signs. It is highly important to recognize, diagnose, and rapidly intervene in similar cases, as data reported long term hippocampal atrophy and long term cognitive and memory impairment when injuries to hippocampus blood supply are left untreated ^[16].

     Our case demonstrates an anterior hippocampus predominantly irrigated by the PCA and it highlights that a damage to the hippocampus can impair memory processes, and due to its vascularization by the PCA, the hippocampus is involved in large territorial strokes from adjacent structures and when affected, clinical symptoms and signs such as amnesia should draw urgent attention.

Conclusion

     Symptoms like visual field defects, confusion, weakness and general status alteration are always associated with stroke to PCA. Due to false negative and radiological delay on early CT scans, brain MRI/MRA done in emergency is essential to ensure a rapid diagnosis and identification of the ischemic area. When there is an isolated hippocampal stroke, TGA is the most apparent symptom of presentation. Usually, the amnesia is transient and resolve within 24 hours after medical therapy.

Declarations

Authorship statement

All authors contributed equally and validated the final version of record.

Conflicts Of Interest

The Author(s) declare(s) that there is no conflict of interest.

Funding statement

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Registration

No registration applicable.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Ethical approval

A written and verbal consent was taken from the patient.

References

1.      Stephens RB, Stilwell DL. Arteries and Veins of the Human Brain. Thomas; 1969. (Thomas books).

2.      Szabo K, Förster A, Jäger T, Kern R, Griebe M, Hennerici MG, et al. Hippocampal Lesion Patterns in Acute Posterior Cerebral Artery Stroke. Stroke. 2009 Jun 1;40(6):2042–5. https://doi.org/10.1161/STROKEAHA.108.536144.

3.      Gass A, Ay H, Szabo K, Koroshetz WJ. Diffusion-weighted MRI for the “small stuff”: the details of acute cerebral ischaemia. Lancet Neurol. 2004;3(1):39–45. https://doi.org/10.1016/s1474-4422(03)006215.

4.      Brandt T, Steinke W, Thie A, Pessin MS, Caplan LR. Posterior cerebral artery territory infarcts: clinical features, infarct topography, causes and outcome. Multicenter results and a review of the literature. Cerebrovasc Dis. 2000;10(3):170–182. https://doi.org/10.1159/000016053.

5.      Koudstaal PJ, van Gijn J, Kappelle LJ. Headache in transient or permanent cerebral ischemia. Dutch TIA Study Group. Stroke. 1991 Jun 1;22(6):754–9. https://doi.org/10.1161/01.STR.22.6.754.

6.      Arena JE, Rabinstein AA. Transient global amnesia. Mayo Clin Proc. 2015;90(2):264–272. https://doi.org/10.1016/j.mayocp.2014.12.001.

7.      Kumral E, Deveci EE, Erdoğan C, Enüstün C. Isolated hippocampal infarcts: Vascular and neuropsychological findings. J Neurol Sci. 2015;356(12):83–89. https://doi.org/10.1016/j.jns.2015.06.01.

8.      Naldi F, Baiardi S, Guarino M, Spinardi L, Cirignotta F, Stracciari A. Posterior hippocampal stroke presenting with transient global amnesia. Neurocase. 2017 Jan 2;23(1):22–5. https://doi.org/10.1080/13554794.2016.1270329.

9.      Bhai S, Biffi A, Bakhadirov K, Prasad S. Complete Anterograde Amnesia From Simultaneous Bilateral Hippocampal Infarction. The Neurohospitalist. 2014 Jul 1;4(3):165–6. https://doi.org/10.1177/1941874414524795.

10. Cipolotti L, Bird CM. Amnesia and the hippocampus. Current Opinion in Neurology. 2006;19(6):593–8. https://doi.org/10.1097/01.wco.0000247608.42320.f9.

11. Sparaco M, Ciolli L, Zini A. Posterior circulation ischaemic stroke—a review part I: anatomy, aetiology and clinical presentations. Neurol Sci. 2019 Oct 1;40(10):1995–2006. https://doi.org/10.1007/s10072-019-03977-2.

12. Arboix A, Arbe G, García-Eroles L, Oliveres M, Parra O, Massons J. Infarctions in the vascular territory of the posterior cerebral artery: clinical features in 232 patients. BMC Res Notes. 2011 Sep 7;4(1):329. https://doi.org/10.1186/1756-0500-4-329.

13. Munk AH, Starup EB, Lambon Ralph MA, Leff AP, Starrfelt R, Robotham RJ. Colour perception deficits after posterior stroke: Not so rare after all? Cortex. 2023 Feb 1;159:118–30. https://doi.org/10.1016/j.cortex.2022.12.001.

14. Hoyer C, Szabo K. Pitfalls in the Diagnosis of Posterior Circulation Stroke in the Emergency Setting. Front Neurol. 2021;12:682827. https://doi.org/10.3389/fneur.2021.682827.

15. Salerno A, Strambo D, Nannoni S, Dunet V, Michel P. Patterns of ischemic posterior circulation strokes: A clinical, anatomical, and radiological review. Int J Stroke. 2022 Aug 1;17(7):714–22. https://doi.org/10.1177/17474930211046758.

16. Caplan LR. UpToDate. 2023. Patient education: Ischemic stroke treatment (Beyond the Basics). Available from: https://www.uptodate.com/contents/ischemic-stroke-treatment-beyond-the-basics#H7298680

17. Coutts SB, Ankolekar S, Appireddy R, Arenillas JF, Assis Z, Bailey P, et al. Tenecteplase versus standard of care for minor ischaemic stroke with proven occlusion (TEMPO-2): a randomised, open label, phase 3 superiority trial. Lancet. 2024 Jun 15;403(10444):2597–605. https://doi.org/10.1016/S0140-6736(24)00921-8.

18. Nguyen TQ, Tran MH, Phung HN, Nguyen KV, Tran HTM, Walter S, et al. Endovascular treatment for acute ischemic stroke beyond the 24-h time window: Selection by target mismatch profile. Int J Stroke. 2024 Mar 1;19(3):305–13. https://doi.org/10.1177/17474930231208817.