By Evangelos Boultoukas

Stroke is the third most common cause of mortality in UK with up to 12% of first strokes occurring in young adults with the annual incidence approaching 10/100000 in UK. Carotid or vertebral dissection represents less than 2% of all ischemic strokes but is over represented in young adults and the most common causes of carotid or vertebral dissection being traumatic, other causes include connective tissue disorders or cystic media necrosis but these are rare.

Case description

A 43-year-old male with insulin dependent diabetes mellitus and hypercholesterolemia presented to A&E with left ptosis and right upper limb weakness after gym workout. The symptoms resolved and he was discharged home. The following day he again presented to the ED again with expressive dysphasia and right upper weakness. These symptoms again resolved within 12 hours and he was again discharged home, however two days later he was admitted to hospital with right sided hemiparesis and expressive aphasia. A CT head (FIGURE 1 below) demonstrated an left middle cerebellar artery (MCA) stroke and he was transferred to a neurosciences centre for consideration of decompressive craniectomy.

CT angiogram and CT perfusion (FIGURE 2) study demonstrated established left MCA infarct and severe ischemia in the left posterior cerebral artery (PCA) distribution, thought at the time to be due to brain herniation and external pressure on the left PCA. He underwent the decompressive craniectomy and was discharged to the ward from the neurocritical care unit five days later.

A subsequent CT angiogram (FIGURE 3) of the head and neck showed a left aortic dissection and a “foetal Left PCA”.

Foetal Posterior Communicating Artery

A foetal PCA (fPCA) is present in up to 30% of individuals. The posterior communicating artery (PCOM), in the presence of a fPCA, is is larger than the P1 segment of the PCA (the P1 segment is usually hypoplastic or even be absent), this means that the majority of the blood supply to the PCA arises from the PCOM (and therefore MCA) rather than the PCA (review, case series). The presence of a fetal PCA following stroke may have devastating consequences because the PCA is perfused by the anterior, rather than the posterior circulation and therefore a MCA infarct can involve the ipsilateral PCA territory.

Legend for Figures

FIGURE 1: (A) CT angiography and (B) plain CT.

FIGURE 2: CT Perfusion (see resources here,  here, and here in addition to those in the text above) CBF = Cerebral Blood Flow, CBV = Cerebral Blood Volume, TTP = Time To Peak, TTD = Time To Drain, PMB = Permeability.

FIGURE 3: Reconstructed CT angiography of the head and neck. Arrow 1 indicates the origin of the Left ICA obstruction. Unfortunately, in this image the tip is slightly hidden by the ECA. Arrow 2 indicates the usual site of the L PCOM, comparison with the R PCOM is revealing. The L MCA is absent due to obstruction.