Agenesis, aplasia and hypoplasia of internal carotid artery (ICA) is a rare congenital anomaly with incidence of < 0.01% in general population. Tode, in 1787, was first to report ICA agenesis on post-mortem exam. Verbiest was first to report the same on angiography in 1954.
Some more than 100 cases have been reported in the past. Padget described that ICA arises from the dorsal aorta and the third aortic arch at 4–5 mm embryonic stage and entirely develops by 6 weeks. This developmental anomaly occurs due to mechanical stress resulting from pressure effects and excessive folding of cephalic portion of embryo and amniotic bands. Also the carotid canal develops in association with the ICA. The skull-base begin to form during the 5th–6th weeks of fetal life. Thus, if ICA does not develop or fails to develop before the 5th embryonic week, the ICA and the carotid canal remains undeveloped[5, 6]. The external carotid artery (ECA) and common carotid artery (CCA) arise from the aortic sac independently and can present normally in a case of ICA agenesis as was seen in our case.
Diagnosis of an absent ICA is made on CT/CT angiography and digital subtraction angiography (DSA). Non-visualization of an ICA on angiography and absent bony carotid canal in the base of the skull on CT is helps in the diagnosis of congenital absence of an ICA.
Most of the patients are asymptomatic because of the collateral circulation. Tsuruta and Myazaki proposed three types of collateral channels through the circle of Willis. In Type I, the ipsilateral ACA is supplied by the contralateral ICA, opposite to the ICA agenesis, through the anterior communicating artery (A.Com.). The MCA is supplied by the basilar artery through the posterior communicating artery. In Type II, the ipsilateral ACA and MCA are supplied by the contralateral ICA through patent A.Com. In Type III, the ipsilateral ACA and MCA are supplied by the transcranial anastomoses that develop from ECA or contralateral ICA or primitive vessels. Our case had Type II anomaly.
Sometimes patients with congenital absent ICA develops subarachnoid hemorrhage (SAH) due to ruptured aneurysm or transient ischemic attack (TIA) due to vascular insufficiency. ICA agenesis has been associated with increased incidence of intracranial aneurysm (25–43%) as compared with general population (2–4%)[12, 4]. Lee et.al. found that aneurysm develops ipsilateral to absent ICA as was in our case, supporting a congenital origin of aneurysm as opposed to hemodynamic factors.
COVID-19 infection occurs through the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virion binding to Angiotensin Converting Enzyme 2 (ACE-2), an enzyme responsible for regulation of blood pressure and has anti-atherosclerotic effects. SARS-CoV-2 binds to Angiotensin Converting Enzyme-2 (ACE-2) and inactivates it. Also, SARS-CoV-2- ACE-2 binding is responsible for direct damage to the BBB[9, 10].
COVID-19 is characterized by cytokine outburst and hyperinflammation, platelet activation, endothelial dysfunction and sepsis related coagulopathy leading to increased risk of aneurysm formation or rupture. Pro-inflammatory cytokines in COVID-19 such as interleukin (IL)-1, IL-6, and TNF are found to be responsible for the loss of vascular integrity. Kandula et al. in his study found that the hypercytokinemia of sHLH (Secondary Hemophagocytic Lymph Histiocytosis) may result in endothelial injury through increased vascular permeability, resultant ischemia of the vascular endothelium, and cell damage. Severe COVID-19 infections have a similar cytokine profile as sHLH. Moriguchi et al. found that cytokine cascade has been directly demonstrated to be responsible for neurological disorders and acute cerebrovascular disease. Brian et. al. in his study suggested that the state of hyperinflammation is responsible for increased chance of aneurysm formation and rupture in patients with COVID-19 infection.
COVID-19 is also responsible for thromboembolic event which was seen in our patient. COVID-19 has an increased incidence of thromboembolic events (TE), Venous TE (VTE) more common than arterial TE (ATE). Some report incidence of (TE) to be 20–30% in COVID-19 patients and some reported up to 40–70% of their cases. This was associated with higher rate of mortality patients with COVID-19 as was in our case.