Repeated cerebellar infarction in the affected nondominant vertebral artery distribution with reversible vertebral artery occlusion elicited by head tilt: illustrative case

Abstract

Background: Bow hunter's syndrome or stroke (BHS) is characterized by rotational vertebrobasilar insufficiency elicited by rotation of the neck. It is caused by dynamic and reversible occlusion of the vertebral artery (VA). Reversible symptoms of rotational vertebrobasilar insufficiency are described as bow hunter's syndrome, although brain infarction is rarely reported as bow hunter's stroke.

Observations: A 70-year-old man experienced repeated cerebellar infarctions three times in the posterior inferior cerebellar artery (PICA) distribution of the nondominant right VA connecting the basilar artery. The onset of symptoms indicating cerebellar infarcts and the patient's head position changes were unrelated. Dynamic digital angiography (DA) revealed that the nondominant right VA was occluded by an osteophyte from the C4 vertebral body, and the right PICA branches were shown to be passing through the distal right VA from the left VA. These findings were observed when the patient's head was tilted to the right. An arterio-arterial embolic mechanism was suggested as the cause of repeated cerebellar infarctions.

Lessons: Transient nondominant VA occlusion has been rarely reported as a cause of BHS when the head is tilted. To confirm the diagnosis of BHS, additional head tilt is recommended when performing dynamic DA in patients with a cervical osteophyte.

Keywords: 3D-CTA = three-dimensional computed tomography angiography; BHS = bow hunter’s syndrome or stroke; DA = digital angiography; DSA = digital subtraction angiography; DWI = diffusion-weighted imaging; MRA = magnetic resonance angiography; MRI = magnetic resonance imaging; PICA = posterior inferior cerebellar artery; VA = vertebral artery; bow hunter’s syndrome; cervical osteophyte; head tilt; repeated cerebellar infarction; stroke; transient vertebral artery occlusion.

FIG. 1.

MRI and MRA on the patient’s first admission to our hospital (A, B, D, and E) and follow-up MRA at his first admission (C and F). A: DWI showing a high signal intensity lesion in the medial right PICA distribution. Brain (B) and cervical (E) MRA on admission. The right VA is not demonstrated. D: FLAIR image showing a previous right cerebellar infarction as a small hypointensity lesion in the lateral right PICA distribution. Brain (C) and cervical (F) MRA 3 days later. The nondominant right VA is observed from the origin to the junction of the left VA and basilar artery. FLAIR = fluid-attenuated inversion recovery.

FIG. 2.

MRI and MRA on the patient’s second admission to our hospital (A, B, D, and E) and follow-up MRA at his second admission (C and F). A: DWI showing a small, high signal intensity lesion in the right side of the inferior cerebellar vermis. Brain (B) and cervical (E) MRA on admission. The right VA is not observed as it was on his previous admission (see Fig. 1B and E). D: FLAIR image showing past cerebellar infarcts in the right PICA distribution as hypointense lesions. Brain (C) and cervical (F) MRA 12 days later. The right VA appears again as previously demonstrated (see Fig. 1C and F).

FIG. 3.

3D-CTA. A: Posterior view with volume-rendering method showing C3–C6 left laminoplasty performed at a previous clinic. B: Coronal reformatted image. An osteophyte of C4 (red arrow) compresses the right VA laterally without stenosis.

FIG. 4.

Dynamic bilateral vertebral arteriography. A–C: DSA of the right VA at the neutral position of the head and neck. The hemispheric (arrows) and vermian (arrowheads) branches of the right PICA are demonstrated by injection of the right VA. A: Anterior-posterior view. B: Lateral view. C: Lateral view of 3D-rotation angiography with the volume-rendering method. D–H: Dynamic DA of the right VA. No stenosis is seen in the right VA at the neutral position (D), rotation of the neck to the right (E) and to the left (F), and head tilt to the left (H). Occlusion of the right VA is demonstrated at C4 level during head tilt to the right (G). I–K: Dynamic DSA of the left VA during head tilt to the right. I and J: Anterior-posterior view. K: Lateral view. The distal portion of the right VA is opacified in a retrograde fashion from the left VA (I), and both PICA hemispheric (arrows) and vermian (arrowheads) branches are subsequently shown (J and K).

FIG. 5.

3D-CTA with volume-rendering method after C3–C6 posterior cervical fixation. A: Anterior view. B: Posterior view. Both VAs are demonstrated without stenosis.