Loss of Consciousness in an Elderly Woman With Prior CVA: What Cause?

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An 88-year-old woman with a history of hypertension and prior CVA was found unresponsive at home by her family. Results of a noncontrast CT of the head obtained in the ED show hypodense lesions in the bilateral thalami extending to the rostral midbrain (Figure 1). (Note: Please click on all images to enlarge)

The patient’s persistent altered mental status prompted an order for an MRI of the brain for further evaluation. Axial FLAIR images show hyperintense signal in the bilateral thalami and midbrain. Encephalomalacia from prior right PCA infarct is also noted (Figure 2).

Axial diffusion-weighted images show restricted diffusion involving the bilateral thalami and extending to the rostral midbrain, corresponding to abnormality observed on CT (Figure 3).

Answers and Discussion on Next Page.

Answers

1. What is the diagnosis?
A. Acute bilateral thalamic infarcts

2. Which of the following vascular structures is affected?
B.Artery of Percheron

3. Arterial supply to the thalami includes branches of which of the following?
D. All of the above(iInternal carotid artery, basilar artery, and posterior cerebral artery)

4. The artery of Percheron is readily visualized on conventional angiography. 
False

Discussion

The bilateral thalami and midbrain have arterial supply from both the internal carotid arteries and the vertebrobasilar arteries. Arterial supply to the paramedian thalami conventionally is provided by multiple small perforating vessels from the bilateral proximal posterior cerebral arteries. The artery of Percheron is an uncommon anatomic variant in which a dominant artery originating from a unilateral proximal posterior cerebral artery (PCA) supplies the bilateral medial thalami and variably, the midbrain.

Figure 4 shows the arterial anatomy to the thalami. The left image shows normal anatomy, with small perforating arteries off the bilateral PCAs. The middle image shows Artery of Percheron, in which the thalamic perforators originate from a unilateral PCA. The right image shows arcade anatomy, with thalamic perforators originating from a bridging artery connecting the bilateral P1 segments.

Artery of Percheron occlusion can present with involvement of the medial thalami, anterior thalami, and midbrain. In one case series, the “V sign” was described, named for the characteristic hyperintense signal along the interpeduncular fossa with midbrain involvement, which was present in our case.

The classic clinical presentation of a bilateral thalamic infarct is disorders of consciousness, memory impairment, and vertical gaze palsy. Mental status changes can vary from drowsiness to coma. Vertical gaze palsy is more often present with lesions that involve the midbrain, and memory impairment is more severe with involvement of the anterior thalamus.

Differential considerations for bilateral thalamic lesions include venous infarct, Wernicke encephalopathy, infection, and infiltrative neoplasm. Specifically, Creutzfeldt-Jakob disease and primary bilateral thalamic glioma can have symmetric bilateral medial thalamic involvement. However, these lesions do not respect vascular territories and do not characteristically involve the midbrain.

References:

1. Hegde AN, Mohan S, Lath N, et al. Differential diagnosis for bilateral abnormalities of the basal ganglia and thalamus. Radiographics. 2011: 31:5-30

2. Lazzaro NA, Wright B, Castillo M, et al. Artery of Percheron infarction: Imaging patterns and clinical spectrum. AJNR Am J Neuroradiol 2010: 31:1283-1289.

3. Matheus MG, Castillo M. Imaging of acute bilateral paramedian thalamic and mesencephalic infarcts. AJNR Am J Neuroradiol. 2003:24:2005-2008.

4. Teoh HL, Ahmad A, Yeo LL, et al. Bilateral thalamic infarcts due to occlusion of artery of Percheron. J Neurol Sci. 2010:293:110-111.