====== Internal carotid artery dysgenesis ====== [[Dysgenesis]] of the [[internal carotid artery]] (ICA) is a broad term comprising [[hypoplasia]], [[aplasia]] and [[agenesis]] of the vessel. It is a rare anomaly, often clinically silent, that can be confidently diagnosed by means of noninvasive imaging methods. The agenesis show complete absence of ICA and the carotid bony canal, whereas hypoplasia shows a small bony [[carotid canal]]. Absence of bony carotid canal on CT scan is a characteristic feature of [[internal carotid artery agenesis]]. In [[1787]], Tode documented the first case of carotid agenesis, identifying it on postmortem examination. In [[1954]], the first case of ICA agenesis at cerebral angiography was reported by [[Henk Verbiest]] ((Kumaresh A, Vasanthraj PK, Chandrasekharan A. Unilateral agenesis of internal carotid artery with intercavernous anastomosis: a rare case report. J Clin Imaging Sci. 2015 Jan 30;5:7. doi: 10.4103/2156-7514.150453. eCollection 2015. PubMed PMID: 25806142; PubMed Central PMCID: PMC4322372. )). see also [[Aberrant internal carotid artery]]. ===== Epidemiology ===== Male predominance has been seen with slightly increased incidence on the left side. Patients with agenesis of ICA are usually asymptomatic due to the collateral circulation from the contralateral ICA and the vertebrobasilar system via the circle of Willis ((Neves WS, Kakudate MY, Cêntola CP, Garzon RP, d›Água AP, Sanches R. Agenesis of the internal carotid artery: A case report. Radiol Bras. 2008;41(1):63–66.)). ===== Etiology ===== Certain mechanical and hemodynamic stresses over the embryo like exaggerated folding of embryo toward one side and constriction by amniotic band have been postulated as hypothesis for agenesis ((Teal JS, Naheedy MH, Hasso AN. Total agenesis of the internalcarotid artery. Am J Neuroradiol. 1980;1:435–42.)) ((Kishore PR, Kaufman AB, Melichar FA. Intrasellar carotid anastomosis simulating pituitary microadenoma. Radiology. 1979;132:381–3.)). ===== Clinical features ===== A few patients occasionally present with headache, SAH, and TIA. Associated abnormalities include vascular aneurysm. Rarely, transsphenoidal encephalocele and rete mirabilis in the cranial base are seen ((Blustajn J, Netchine I, Frédy D, Bakouche P, Piekarski JD, Meder JF. Dysgenesis of the internal carotid artery associated with transsphenoidal encephalocele: a neural crest syndrome? AJNR Am J Neuroradiol. 1999 Jun-Jul;20(6):1154-7. PubMed PMID: 10445462. )). ===== Case series ===== Two original cases of internal carotid artery dysgenesis associated with a malformative spectrum, which includes transsphenoidal encephalocele, optic nerve coloboma, hypopituitarism, and hypertelorism. Cephalic neural crest cells migrate to various regions in the head and neck where they contribute to the development of structures as diverse as the anterior skull base, the walls of the craniofacial arteries, the forebrain, and the face. Data suggest that the link between these rare malformations is abnormal neural crest development ((Blustajn J, Netchine I, Frédy D, Bakouche P, Piekarski JD, Meder JF. Dysgenesis of the internal carotid artery associated with transsphenoidal encephalocele: a neural crest syndrome? AJNR Am J Neuroradiol. 1999 Jun-Jul;20(6):1154-7. PubMed PMID: 10445462. )). ---- After a review of teaching files, 7 patients with unilateral carotid dysgenesis were found, 2 with agenesis of the ICA, 3 with carotid aplasia, and 2 with hypoplasia of the vessel. Computed tomography (CT) and magnetic resonance angiography (MRA) of the brain were performed in all patients, with a complete magnetic resonance of the brain in 3 of them, a CT angiography of the brain in one, and MRA of the cervical arteries in 3. The fetal pattern of arterial circulation was found in 3 patients with agenesis/aplasia of the ICA and the adult pattern was found in 2 patients, being the brain circulation of normal pattern in the patients with hypoplasia of the ICA. Two patients presented signs of reduced flow to the brain hemisphere ipsilateral to the carotid dysgenesis; one of them with an old homolateral brain infarction. Far from being just an anatomic curiosity, the dysgenesis of the ICA may have serious consequences if not recognized prior to endarterectomies, carotid ligation or transsphenoidal surgery. As much as one-third of these patients will have intracranial aneurysms as well. The imaging methods, instead being mutually exclusive, are complementary in the evaluation of carotid dysgenesis ((de Mendonça JL, Viana SL, Freitas FM, Matos Vde L, Viana MA, Faria e Silva R, Quaglia LA, Guerra JG. Unilateral dysgenesis of the internal carotid artery: spectrum of imaging findings. Can Assoc Radiol J. 2008 Apr;59(2):61-9. Review. PubMed PMID: 18533394. )). ===== Case reports ===== Tsukano et al. describe a [[case]] of acute [[middle cerebral artery occlusion]] in a patient with ipsilateral [[internal carotid artery]] [[dysgenesis]] successfully treated with [[mechanical thrombectomy]] utilising a collateral pathway. During the [[procedure]], a triaxial system using a [[balloon]] guiding catheter, flexible large lumen aspiration catheter and [[stent retriever]] was advanced from the left [[vertebral artery]] to the occluded left [[middle cerebral artery]] through the left [[posterior communicating artery]]. Because proximal aspiration from the balloon guiding catheter alone might have insufficient suction force due to the retrograde blood flow from large vascular communications (e.g. vertebral artery union), the tip of the flexible large lumen aspiration catheter was set at the proximal left middle cerebral artery, and distal aspiration was added during stent retrieval. A [[thrombolysis]] in cerebral [[infarction]] 2b result was achieved after the first pass. In this case, identification of [[carotid canal]] [[hypoplasia]] on [[computed tomography]] allowed for an immediate attempt of this alternative approach, avoiding a delay in the time to [[reperfusion]] ((Tsukano J, Kurabe S, Sugai T, Wada M, Kumagai T. Mechanical thrombectomy utilising a collateral pathway in a patient with dysgenesis of the internal carotid artery. Interv Neuroradiol. 2018 Sep 12:1591019918799303. doi: 10.1177/1591019918799303. [Epub ahead of print] PubMed PMID: 30205728. )). ---- A 58-year-old man with a history of myocardial infarction and diabetes mellitus presented with sudden-onset difficulty in speaking, numbness on the left side of the face, and weakness of the left arm and leg. Neurological examination revealed dysarthria, left facial paralysis, left hemiparesis, and bilateral absence of the plantar reflexes. Diffusion-weighted magnetic resonance imaging showed a right middle cerebral artery (MCA) infarction. On cranial and cervical magnetic resonance angiography, the left ICA could not be seen distal to the bifurcation; the left MCA was supplied through an intercavernous anastomosis between the right ICA and the left ICA. Cranial computed tomography (CT) revealed the absence of the left carotid canal. Digital subtraction angiography led to a diagnosis of left ICA agenesis with an intercavernous anastomosis. The patient was discharged on acetylsalicylic acid and warfarin. ICA agenesis with an intercavernous anastomosis is a rare vascular anomaly that should be differentiated from secondary causes of ICA stenosis and occlusions by showing agenesis of the carotid canal on cranial CT ((Erdogan M, Senadim S, Ince Yasinoglu KN, Selcuk HH, Atakli HD. Internal Carotid Artery Agenesis with an Intercavernous Anastomosis: A Rare Case. J Stroke Cerebrovasc Dis. 2017 Aug 3. pii: S1052-3057(17)30351-8. doi: 10.1016/j.jstrokecerebrovasdis.2017.06.055. [Epub ahead of print] PubMed PMID: 28781055. )).