Artery of Percheron infarct: a diagnostic challenge

Abstract

The artery of Percheron is a rare anatomical variation that supplies thalamus and the midbrain. A stroke in this area is a rare event. The presentation varies widely, with some bizarre disturbances, like transient episodic loss of consciousness similar to coma, somnolence, cognition and memory impairment and psychosis. We report a case of a patient who presented at the emergency department with a sudden change of consciousness. During the observation, she oscillated reactive state of consciousness with obnubilation similar to coma. The first exams were normal, which include a cranial CT of the brain, and so the patient was kept under observation. The final diagnosis was only possible 24 hours later with cranial CT where an ischaemic lesion on the Percheron territory was identified. This case highlights an unusual clinic and a difficult neuroimaging stroke diagnosis of a rare condition, that is unknown to most of the physicians.

Background

The artery of Percheron (AOP) is an uncommon anatomic variant of the blood vessels, in which a single, unpaired perforating artery trunk arises from the posterior cerebral artery and supplies bilateral medial thalamus and a variable contribution of the midbrain. Occlusion of the AOP is one of the few single artery pathologies that can affect bilateral structures. A lesion in this area may manifest with a wide range of manifestations like altered mental status, coma, transient episodic loss of consciousness, memory impairment, psychosis and oculomotor dysfunction. The diagnosis is often missed due to the unusual symptoms and because the image study usually does not show abnormalities, the occlusions in such small calibre arteries are usually not visible. This affects the treatment and the prognosis of this pathology.

Case presentation

A 77-year-old woman, with no physical limitation, was found unresponsive in the morning and taken to the emergency department in a stuporous state. She lived with her husband who had seen her, in her normal state 2 hours before. He denies any other symptoms, drugs consumption or recent change in medication. The patient has a history of hypertension, atrial fibrillation (non-hypocoagulated) and a cerebral haemorrhage due to a cerebral aneurism rupture, having another one in surveillance in neurosurgery consultation.

Physical exam on admission to the emergency department revealed a stuporous and non-verbal patient with a Glasgow of 8/15 (O1V2M5), afebrile with a blood pressure of 150/77 mm Hg, an arrhythmic heart rate of 87 bpm, with no cardiovascular, respiratory or abdominal alterations. On neurologic exam, pupils were miotic, with slight reaction to light, no alteration in facial mimic or motor alterations were observed, plantar response was flexor on both sides. During the period in which she was under observation in the emergency department, the patient alternated periods of normal state of consciousness, when she only complained of diplopia, with periods of stuporous/hypersomnolence and non-reaction to verbal or physical stimulus.

A cranial CT without contrast was performed and revealed no acute intracranial pathology followed by an angiography that also did not show any signs of acute lesions. At the time, it was not possible to perform cerebral MRI, and so the patient was kept under surveillance in the emergency department. Thus, due to the oscillation of the neurologic state, a stroke was considered a less likely condition, so invasive therapy such as thrombolysis was not performed, but was given 500 mg of aspirin. It was also considered as a postictal state, and so the patient was medicated with antiepileptics. Twenty-four hours later a new cranial CT (figure 1) was performed. At this time, hypodensities in both ventral portions of both side of thalamus were observed, symmetrically distributed, with extension to the midbrain, that could suggest a recent vascular lesion on the Percheron artery territory, but further exams were necessary to confirm. So, the patient was admitted to the Internal Medicine care for further investigation.

Figure 1.

CT image, on the left CT of admission where no lesion was observed; and the two right CT images, 24 hours later, with hypodensities in the ventral portion of both thalamus with extension to the midbrain.

During hospitalisation, the patient was under the guidance of a multidisciplinary team with Internal Medicine, Neurology, Immuno-Hemotherapy, Neurosurgery and Psychiatry. She maintained fluctuations in consciousness, with periods of apathy and somnolence versus periods of awareness with changes in memory and on cognitive impairment (could not identify special dates or important people; write or remember how to do some basic daily activities) and diplopia. Later, a cerebral MRI (figure 2) was performed and confirmed subacute infarction in the bilateral thalamus extending towards the ventral midbrain, compatible with a stroke of the Percheron area, and another recent ischaemic lesion between the right median cerebral artery and the right posterior cerebral artery was also seen. The rest of the exams were unremarkable except the echocardiography where a slight aortic stenosis was detected, and the ECG where atrial fibrillation was identified.

Figure 2.

Cerebral MRI image shows subacute infarction in the bilateral thalami extending towards the ventral midbrain, compatible with a stroke of the Percheron area, and another recent ischaemic lesion between the right median cerebral artery and the right posterior cerebral artery.

The patient was discharged 20 days later, with slight clinical improvement, maintaining fluctuation of consciousness, somnolence and changes of memory and cognitive impairment. During hospitalisation she was on rehabilitation programme, that was continued after discharged.

Treatment

Our patient was started on antiepileptics in the emergency department because of the suspicion of postcritical state, which is one of the differential diagnosis that was considered. They were suspended due to the lack of evidence of seizures or other signs or symptoms that could elevate the risk of an epileptic pathology.

Even being within the indication period for thrombolysis, due to the lack of clinical and imaging of an ischaemic aetiology, this treatment was not performed. But antiplatelet and antidyslipidaemic drugs (500 mg of aspirin first and then 100 mg and 20 mg of atorvastatin) were started, as indicated in the most recent guidelines.

During hospitalisation, warfarin was initiated because of the thromboembolic risk (CHA2DS2VASc Score of 6 and HAS-BLED of 3) due to atrial fibrillation. Since the patient had a history of cerebral haemorrhage of a rupture of a cerebral aneurysm, the risk and benefits in this particular situation were discussed with the neurosurgeon, and it was decided that hipocoagulation with warfarin was the best treatment option at that time, and it was also the family preference. Additionally, a motor and psychologic rehabilitation programme was initiated, in which the patient remained ambulatory.

Outcome and follow-up

Even after starting the rehabilitation programme and the treatment, the patient maintained the fluctuation of consciousness, with hypersomnolence, cognition and memory impairment and apathy being the most prominent.

The patient is now followed in Internal Medicine, Cardiology and Physical Medicine and Rehabilitation.

Discussion

The AOP is a rare anatomical variant where a single thalamic perforating artery arises from the proximal posterior cerebral artery between the basilar artery and the posterior communicating artery and supplies the rostral mesencephalon and both paramedian thalamic zone.¹ An occlusion of this artery may affect various thalamic nuclei with or without involvement of the rostral midbrain, which means that is possible to have several possible clinical pictures.

The thalamus is composed of several nuclei and serves as control centre of several neurological domains, such as sensation, movement, arousal, cognition, behaviour and emotions. Consequently, insults affecting the thalamus have the potential to affect many different neurologic functions and cause a diverse set of deficits.² The diagnosis of a lesion in this area is a challenge due to the variety of possible symptoms. The most described classic features are somnolence and fluctuations in consciousness, vertical gaze palsy and cognitive impairment.¹ But it is possible to have other presentations, that manifest as focal lesions like aphasia, dysarthria or oculomotor disturbance. Our patient had a variable wide presentation, with some of the classical symptoms such as the somnolence, fluctuations in consciousness and cognitive impairment and one focal lesion, diplopia. The most important clinical feature was the fluctuations of consciousness, because it led to the suspicion of other neurological conditions, and consequently delayed the diagnosis and treatment that could change the prognostic.

The most frequent causes of stroke in patients with bilateral thalamic involvement are small vessel disease, and embolic origin³ being the last. This patient had the diagnosis of atrial fibrillation in a recent time, but it was chosen by his attending physician not to start hypocoagulation treatment because of the cerebral aneurism history. During hospitalisation the benefits and risks were discussed with the neurosurgeon and it was decided to initiate treatment with hypocoagulation, since there was not any absolute contraindication for this sort of therapy.

The CT scan and angiography usually do not show abnormalities in acute stroke of this area, because the occlusions in such small calibre arteries are usually not visible. The cerebral MRI is the best imaging to establish the diagnoses. Because of the inability of most hospitals to perform a cerebral MRI in the first hours of symptoms, most of the patients go undiagnosed. Also, due to this delay and the non-specificity of the symptoms, usually patients suffering of a stroke in this area do not receive thrombolysis or other acute treatment, that can be used in this small vessel stroke.⁴ Contrary to the usual, in our patient, the CT scan was already possible to identify ischaemic lesions suggestive of bilateral thalamic infarction in the region of Percheron artery. In the MRI, the lesion was even more evident, leading to confirmation. Although the CT scan shows a suggestive ischaemic lesion, it appeared only 24 hours after the event, so no acute therapeutic intervention was made. Since MRI is the most specific and sensible exam to identify this sort of lesion, if it was widely accessible probably this kind of stroke could be more diagnosed.

The prognostic depends on which area is affected.³ In some studies, it was concluded that when the midbrain was involved the outcome was unfavourable. In our case, the patient did not recover to her usual state, she kept the fluctuation of consciousness and oculomotor disturbance, but had some improvement in the memory and cognitive impairment, which were even better after the patient started physical and functional rehabilitation.

The sequelae described are the most typical for an ischaemic event in the territory of Percheron artery, and this case shows how it can be difficult to diagnose due to its non-specificity. The diagnosis is usually delayed, consequently, the patients do not receive an acute treatment, which worsens the prognostic. The hypocoagulation is also relevant, considering the pathological history and new findings, requiring a careful assessment of risks and benefits on a case-by-case basis. This case intended to alert to consider this kind of stroke when the neurologic symptoms are unspecific.

Learning points.

• The artery of Percheron is a rare anatomical variation which supplies thalamus and the midbrain, which can lead to a variable wide presentation, like somnolence and fluctuations in consciousness, memory impairment, psychosis and oculomotor dysfunction.

• A stroke in the anatomic area supplied by Percheron artery is a rare disease with unusual clinical presentation and is usually associated with small vessel disease or a embolic disease as atrial fibrillation.

• The diagnosis is often missed due to the unusual symptoms and also because the lesion may not be visualised on primary imaging like CT scan, cerebral MRI being more sensible for the diagnoses.

• The treatment, such as intravenous thrombolysis can be performed if the diagnosis of acute stroke is made, but generally due to a late-stage diagnosis, this therapy is ineffective and dangerous.