Member Login December 2007 Case of the Month  Compiled by:  Hadassah Lipstein, MD   History:  8 year old female with severe headaches. Follow-up of known congenital anomaly.   Exam:  Long- and short- axis, fat and water weighted sequences were obtained through the brain.  Non-contrast MRA of the carotid arteries and circle of Willis was also performed utilizing TOF and MIP algorithms.   Findings: There is absence of the left internal carotid artery flow void, and probable absence of the left A1 segment flow void.  No flow signal or vessel is identified within the left cavernous sinus. Collateral vessel from the contralateral M1 and a prominent left P-com supplying the left MCA are noted.  A prominent A-com supplies the left ACA.  A small pituitary gland is seen.   The left vertebral artery and external carotid artery are diminutive in caliber but are patent. The left internal carotid artery is not present. A normal right carotid artery and bifurcation are identified. Images: Fig 1: Axial T2W image demonstrating normal R ICA flow void (green arrow) and absent L ICA flow void (yellow arrow).  Fig 2: Axial T2W image demonstrates absent L A1 segment flow void.  Fig 3: Sagittal T1W image reveals small pituitary gland. Fig 4: Raw data slab from MRA demonstrating no signal in the topography of the L petrous portion of the ICA.  Fig 5: MIP image from MRA demonstrating dilated L Pcom (green arrow) supplying the L MCA and prominent Acom (yellow arrowhead) supplying the L ACA.  Fig 6 and 7: MIP images from MRA demonstrating absent L carotid bifurcation (green arrow, Fig 6) and normal R carotid bifurcation (green arrow, Fig 7). Normal codominant vertebral arteries. (yellow arrows)  Fig 8: Modified from the AJNR, 2001;22: 1957 – Pathways of collateral blood flow.  Images:   Figure 1                                                                                                        Figure 2   Figure 3                                                                                                      Figure 4   Figure 5                                                                                                      Figure 6 Figure 7 Diagnosis: Unilateral agenesis or aplasia of the left internal carotid artery with fetal type collateralization.    Discussion:  Unilateral agenesis, aplasia or hypoplasia of the internal carotid artery is a rare congenital anomaly, with a reported incidence of < 0.01% of the population. Agenesis is defined as complete failure of an organ to develop.  Aplasia is lack of development.  However, a precursor existed at one time.  Hypoplasia is the incomplete development.  The etiology is unknown, but is thought to be related to some type of insult early in embryogenesis.  The origin of the ICA is from the 3rd aortic arch of the dorsal aorta, at approximately the 4-5 week embryonic stage.  Full development is at approximately 6 weeks.   Unilateral agenesis may be asymptomatic or associated with TIAs and hemorrhage.  It may be a solitary anomaly or associated with complex vascular malformations. Association with small pituitary and hypopituitarism has also been reported in the literature. There is a 24-36% increase incidence of aneurysm. Three main types of collateralization are seen: (Fig 8) Fetal type Adult type Distal ICA type   With the fetal-type, which is most common, seen in our example, a dilated P-com supplies the ipsilateral MCA and a patent A-com supplies the ACA. In the adult type, both the ACA and MCA are supplied by a prominent A-com.  In the distal ICA type, which is least common, transcranial anastomoses develop from the ECA, contralateral ICA or primitive vessels.   References: Naeini, RM, et al., Unilateral Agenesis of the ICA with Ophthalmic Artery Arising from the Posterior  Communicating Artery; AJR, 2005;184:571-73 Feng, Tao et al., Congenital Absence of the Left ICA Associated with Aberrant Intracranial Arterial Circulation. Applied Radiology Online, 2005;34 Given, CA et al., Congenital Absence of the ICA: Case Reports and Review of the Collateral Circulation. AJNR, 2001;22:1953-59 Terms of Use Privacy Statement HIPAA Privacy Practices Careers Site Map Copyright © 2010 by ProScan Imaging