Images in Neurosurgery
Persistent first intersegmental artery:
A craniovertebral vertebral artery variant with implications on C1 lateral mass screw placement
A 65-year-old man presented to the emergency department with transient right-sided visual field deficit. He underwent a stroke workup demonstrating left-sided carotid stenosis on CT angiogram and diffusion-weighted imaging hits in the left occipital lobe on MRI. The patient was scheduled for a diagnostic angiogram to evaluate for carotid stenosis as well as to evaluate for intracranial atherosclerotic disease in the left posterior cerebral artery. The angiogram demonstrated a vertebral artery (VA) variation at the craniovertebral junction called the persistent first intersegmental artery (FIA) with a VA fenestration (Figure 1 and Figure 2). In this variation, the anomalous VA (called the FIA) enters the spinal canal between C1 and C2, and a fenestration of the VA follows a normal course in the C1 sulcus arteriosus and joins with the anomalous VA in the spinal canal. This craniovertebral VA variant is present in only 0.9% of patients. Other craniovertebral VA variations include persistent FIA without fenestration (3.2% of patients) and extracranial C1-2 origin of the posterior inferior cerebellar artery (1.1% of patients). Craniovertebral VA variants are important to recognize because they pass dorsal to the C1 lateral mass and may affect safe screw placement. The remainder of the angiogram demonstrated less than 70% left-sided carotid stenosis. The patient was diagnosed with atrial fibrillation and started on oral anticoagulation.
Figure 1: Right vertebral artery anteroposterior (A) and lateral (B) projections demonstrating a vertebral artery (VA) variation at the craniovertebral junction called the persistent first intersegmental artery (white arrow) with a VA fenestration (red arrow).
Figure 2: CT angiogram coronal (A) view demonstrating a right-sided persistent first intersegmental artery running dorsal to the C1 lateral mass (white arrow) and a normal left-sided vertebral artery running in the C1 sulcus arteriosus (brown arrow). CT angiogram sagittal views (B and C) demonstrating a normal left-sided VA running in the sulcus arteriosus (brown arrow) and a right-sided persistent intersegmental artery running dorsal to the C1 lateral mass (white arrow). Craniovertebral VA variants are important to recognize because they pass dorsal to the C1 lateral mass and may affect safe screw placement.
Abtahi AA, Brodke DS, Lawrence BD. Vertebral Artery Anomalies at the Craniovertebral Junction: A Case Report and Review of the Literature. Evid Based Spine Care J. 2014 Oct; 5(2):
Submitted by: Rimal Dossani MD, Muhammad Waqas MD, Michael Tso MD PhD, Elad I. Levy, MD - University at Buffalo, Department of Neurosurgery