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Congenital absence or hypoplasia of the carotid artery: Radioclinical issues
Congenital Absence or Hypoplasia of the Carotid Artery: Radioclinical Issues Mustafa Tas¸ar, MD,* Sertac¸ Yetis¸er, MD,† Ays¸in Tas¸ar, MD,‡ S ¸ ahin Ug˘urel, MD,* Engin Go¨nu¨l, MD,§ and Mutlu Sag˘lam, MD* Purpose: Congenital anomaly of the carotid artery is a rare abnormality. It is usually discovered incidentally by color Doppler carotid sonography, angiography, computed tomography (CT), or magnetic resonance imaging (MRI) of the head and neck taken for some other reason. Most patients are not symptomatic because of sufficient cerebral circulation supplied to the defective area by the communicating arteries of the circle of Willis, intercavernous anastomosis, communicating arteries from external carotid artery, and by persistent embryologic arteries to the carotid artery territory. However, sometimes, this anatomic variation may eventually lead to some clinical signs and symptoms in particular circumstances in the head and neck of which surgeons are unaware. A retrospective study was designed to emphasize the characteristic radiologic and clinical picture in patients with the congenital absence (agenesis and aplasia) or hypoplasia of the carotid artery, to delineate the associated abnormalities and existing collateral vessels, and to find out its incidence. Material and Methods: Five thousand one hundred cerebral MRI and/or catheter angiograms performed between February 1988 and March 2002 were reviewed for carotid artery abnormality. Results: Seven patients with congenital absence or hypoplasia (4 of these patients were presented with hypoplasia of internal carotid artery [ICA], 3 with absence of ICA) of ICA were identified (0.13%). The radiologic and clinical study of 5 patients with unilateral (3 of these patients were presented with hypoplasia and 2 with absence of ICA) and 2 patients with bilateral (1 was presented with absence of ICA, whereas the other was hypoplasia) congenital abnormality with absence or hypoplasia of ICA demonstrate that those patients are usually asymptomatic and they are diagnosed incidentally. Conclusion: It has been concluded that the combined use of magnetic resonance angiography and CT scanning of the skull base may disclose small but patent ICA. Collateral vessels seem to be usual in such cases, but they may be prominent in cases of acquired vascular occlusion, or increased hemodynamic pressure in dysplastic changes in collateral arteries are known causes of aneurysms. The main vascular supply for the brain in patients with congenitally small (hypoplasia) or absent (agenesis or aplasia) ICA is the vertebrobasilar system in bilateral cases. However, contralateral carotid vessel is the dominant arterial supply for unilateral cases, which has to be borne in mind in surgical interventions to the involved side. (Am J Otolaryngol 2004;25:339-349. © 2004 Elsevier Inc. All rights reserved.)
Congenital absence (agenesis, aplasia) or hypoplasia of one or both internal carotid arteries (ICAs) is a rare developmental abnormality and is discovered incidentally by color Doppler carotid sonography, angiography, computed tomography (CT), or mag-
From the Departments of *Radiology; †ENT; ‡Pediatrics; and §Neurosurgery, Ankara Hospital of Ministry of Health, Ankara, Turkey. Address correspondence to: Mustafa Tasar, MD, Gu¨lhane Medical School, Department of ORL & HNS, 06018 Etlik, Ankara, Turkey. E-mail: [email protected]. © 2004 Elsevier Inc. All rights reserved. 0196-0709/$ - see front matter doi:10.1016/j.amjoto.2004.04.008
netic resonance imaging (MRI) of the head and neck taken for some other reason.1-3 The incidence of the absence of ICA has been reported to be around 0.01%.4-7 The term of the absence of carotid artery has been substituted for the agenesis, aplasia, or hypoplasia of the ICA, which may lead to some misunderstanding because the descriptive classification of this anomaly is lacking.8 It should be kept in mind that the term of hypoplasia here means the underdeveloped carotid with small caliber. These developmental anomalies of ICA are strongly suggested when the carotid canal is absent or hypoplasic as seen on CT scanning of the skull base.2,6,9 Absence of blood flow in the
American Journal of Otolaryngology, Vol 25, No 5 (September-October), 2004: pp 339-349
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carotid because of absence of vessel lumen should be confirmed by angiography. Most patients are not symptomatic because of sufficient cerebral circulation supplied to the defective area by the communicating arteries of the circle of Willis, intercavernous anastomosis, communicating arteries from external carotid artery, and by persistent embryologic arteries to the carotid artery territory.10-17 They live for years without any symptom. However, in some patients, symptoms related with cerebral ischemia because of less blood flow can occur and enlargement of collateral vessels may lead to associated intracranial aneurysm with obvious problems.18,19 It is important to realize the clinical characteristics, imaging features, and surgical implications of this entity because coexisting symptoms may lead the patients to have invasive and risky interventions. The aim of this study is to emphasize the characteristic radiologic and clinical picture in patients with absence or hypoplasia of carotid artery, to delineate the associated abnormalities and existing collateral vessels, and to find out its incidence. MATERIALS AND METHODS Five thousand one hundred cerebral MRI and/or catheter angiograms performed between February 1988 and March 2002 in our department were reviewed and 7 patients with congenital absence or hypoplasia of ICA (5 unilateral and 2 bilateral) were identified. Of all 5 patients, 2 were with absence and 3 were with hypoplasia of ICA; of 2 bilateral cases, one was presented with bilateral absence and the other was presented with hypoplasia. All cases were documented clinically and radiologically by conventional MRI or by other magnetic resonance angiography (MRA) techniques. One bilateral and 4 unilateral absences of ICA were also examined by digital subtraction angiography (DSA). Two bilateral and 4 unilateral cases were also examined by color Doppler ultrasonography. All patients were examined by 1.5 T MR systems (Magnetom SP 63 or Magnetom Vision Plus, Siemens, Erlengen, Germany). Axial T1-weighted and T2-weighted (spin echo proton density, turbo spin echo, and fluid attenuated inversion recovery) sequences were obtained with head coil in supine position. Diffusion-weighted images (b0, b500, b1000 s/mm2) were obtained from 3 patients to exclude acute ischemic lesions and apparent diffusion coefficient maps created (after 1999). The clinical and radiologic data of the patients are shown in Table 1.
TAS¸ AR ET AL
Super selective catheterization (Digitron II and Multistar Plus, Erlengen, Germany) of both internal and external carotid and vertebral arteries were performed under local anesthesia via femoral artery. Two different CT scanners were used for brain imaging including the skull base and the temporal bone with 2-mm slice thickness (Somotom DRH, Siemens, Erlengen, Germany and GE Hi-Speed Advantage, General Electric, Milwaukee, WI). CT angiograms were also obtained with spiral CT scanner. Skull base and the bony carotid canal were assessed on each CT image. If the bony carotid canal was not visible at the serial cuts of the base of the skull, then this abnormality was defined as the absence of the carotid canal and carotid artery. If the bony canal was present, the diameter of the pathological side was compared with that of contralateral part. In suspected bilateral cases, diameter of the canal was compared with that of normal side in patients with unilateral ICA hypoplasia. If the diameter was less than half of the size of normal, then it was accepted as abnormal. However, the patency of the abnormal artery was always controlled with the angiography. In cases with absent ICA, the presence of collateral vessels and other clinical and radiological abnormalities were investigated. Color Doppler sonography was performed with 2 different devices (Acuson XP/10 and Toshiba SS270 A, Tokyo, Japan). B-mode and pulsed-wave color Doppler images were obtained through both common and ICAs, and then blood flow velocity measurements were made.
RESULTS Three of 5 patients with unilateral agenesis or hypoplasia and 2 patients with bilateral absence or hypoplasia were male. The common symptom for all patients was headache. CT revealed intracerebral and subarachnoid hemorrhage in 1 patient with brief and sudden loss of consciousness and in another one with a history of pituitary hypogonadism and chronic headache. Ruptured left middle cerebral artery (MCA) aneurysm and aortic arch abnormality, which was presumably related to the patient’s headache in both patients, was shown. It was revealed that the left common carotid artery and brachiocephalic trunk was running very close to each other as if a single vessel (case 6) (Fig 1). Unilateral absence (agenesis) of the ICA was considered as the probable cause of the hypogonadism. In 1 patient (left hypoplasia) with spontaneous epistaxis from time to time in addition to the headache, CT and DSA revealed nasopharyngeal intense enhancing mass consistent with the angiofibroma (case 7) (Fig 2).
Patient No. Age/Sex
Presenting Complaints
CDUS and US
CT
Diffusion- and Perfusion-weighted Abnormality MR MRA MRI DSA Side
Type of Abnormality
Main Collateral Flow
Associated Abnormalities
⫹
⫹
N
⫺
Left
Hypoplasia
PCOM ACOM
⫺
⫹
⫹
⫺
⫹
Bilateral
Hypoplasia
PCOM ACOM intercavernous anastomoses
⫺
⫺
⫹
⫹
N
⫺
Bilateral
⫹
⫹
⫺
⫹
Right
Hypoplastic bony carotid canal Hypoplastic CCA intracerebral/ subarachnoid hemorrhage
⫹
⫹
N
⫹
Left
PCOM ACOM ACOM PCOM ACOM PCOM
⫺
⫺
Absence (agenesis) Absence (agenesis) Hypoplasia
⫹
⫹
⫺
⫹
Left
Absence of ACOM ICA and PCOM hypoplastic CCA
Small CCA Left hypoplastic and bony carotid hypoplastic canal ICA
⫹
⫹
⫺
⫹
Left
ACOM PCOM
1
53/M
Headache
NA
2
25/M
Headache
3
57/M
Headache
4
17/F
5
55/F
Headache, syncope Headache
Bilateral small CCA and cervical ICA Bilateral small CCA ⫺
6
17/M
Headache, Hypoplastic loss of CCA and conciousness absenct ICA
7
21/M
Headache, episodic nose bleeding
ICA absent
Hypoplastic bony carotid canal Bilateral hypoplastic carotid canal
hypoplasia
CONGENITAL ABSENCE OR HYPOPLASIA
TABLE 1. Clinical and Radiologic Findings of the Patients
⫺ ⫺
Arcus aorta abnormality, primary hypogonadism, noduler goitre, left intracerebral hematoma Nasopharynx angiofibroma
Abbreviations: N, normal; CCA, common carotid artery; ICA, internal carotid artery; US, ultrasonography; CDUS, color Doppler ultrasonography; M, male; F, female; ACOM, anterior communicant artery; PCOM, posterior communicant artery.
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Fig 1. Left ICA agenesis in a patient with hypogonodism, anomaly of the arcus aorta, and the ruptured aneurysm. (A) Digital subtruction angiography of the arcus aorta. Brachiosephalic trunk, thin left CCA and left subclavian artery are running very close to each other. Note that left CCA is thinner than right ICA. (B) Selective left CCA angiography shows marked left ECA and absence of the left ICA. (C) Left CCA is smaller than right CCA as seen on the axial contrast enhanced computed tomography of the neck.
Color Doppler sonography and angiography showed small caliber of CCA in 2 bilateral cases (cases 2 and 3) (Figs 3 and 4). CCA continued as the external carotid artery and no ICA was present in 3 of 4 patients with unilateral carotid abnormality (2 hypoplasia, 1 absence) (cases 5, 6, and 7). Skull base and temporal bone CT scans revealed significantly narrow carotid canal in 1 patient with bilateral hypoplasia of ICA. Carotid canal was also very small in 3 patients with unilateral hypoplasia. One patient with unilateral agenesis could not be scanned with CT (case 4) and angiography revealed the entity
(Fig 5). Although left intracerebral hematoma with subarachnoid hemorrhage was evident in 1 of 6 patients examined by CT (case 6) (Fig 1), brain CT images of other 5 cases were normal. MRA images were in well accordance with DSA images. Diffusion images in 2 patients with leftsided agenesis were unremarkable (cases 5 and 7) (Fig 6). DISCUSSION ICA is one of the most stable arteries of the human body. It rarely shows abnormal devel-
CONGENITAL ABSENCE OR HYPOPLASIA
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Fig 2. Left ICA hypoplasia in a patient with nasopharyngeal angiofibroma. (A) Arcus aorta angiography shows hypoplasic left CCA and hypertrophic left vertebral artery. (B) Selective left CCA angiography reveals a staining nasopharyngeal mass and complete absence of left ICA. (C) Axial contrast enhanced computed tomography scan of the neck shows large caliper right CCA and left vertebral artery and left CCA with small caliper. (D) Axial noncontrasted computed tomography of the skull base with bone windowing reveals hypoplasic left carotid canal (arrowhead).
opment. Tode reported the first case of ICA agenesis in 1787, which was accidentally encountered after a cadaveric dissection.11,20 The prevalence of congenital absence of ICA is estimated as 0.01%.18,21 The prevalence of absence of ICA is 0.058% and the prevalence of hypoplasia of ICA is 0.079% in our series. Unilateral absence or hypoplasia of ICA is more frequent on the left and bilateral absence or hypoplasia is more exceptional and reported to be less than 10% of unilateral involvement. On the other hand, it is one of the
major concerns that the reported incidences are likely not to be realistic because there seems to be some confusion in terminology. It is better to classify dysgenesis of the carotid artery in 3 subgroups as agenesis, aplasia, and hypoplasia. ICA with small caliber and patent lumen corresponds to hypoplasia. Aplasia indicates a vascular remnant, which has no vascular formation. The etiology of agenesis, aplasia, and hypoplasia of ICA is still unknown. There are conflicting proposals for the maldevelopment
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Fig 3. Bilateral ICA agenesis in a patient with no other radiologic finding and clinical symptom. (A) MRA with the 3-dimensional time of flight technique. The anteroposterior projection of MRA shows the extremely tortuous and hypertrophic vertebrobasilar system and absence of both ICA. (B) Axial contrast enhanced computed tomography (CECT) scan of the posterior fossa shows hypertrofic and tortuous vertebrobasilar system. (C) Axial CECT scan of the supratentorial region of the brain shows collateral supply to both cerebral hemisphere via hypertrophic posterior communicant artery and parasellar anostomotic collateral vessels. (D) Axial noncontrast computed tomography scans of the skull base shows both hypoplastic carotid canals.
of this artery. One of the theories indicates a secondary regression of the ICA from the beginning of the intrauterine life. However, the other one claims interruption of the development of the artery for unknown causes after a period of normal growth, which may justify the difference between the loss of maturity in some and absence of the artery in others. Lasjaunias and Santoyo-Vazquez22 have indicated that 7 different embryological segment branches come together and forms the internal
carotid artery system. Those are cervical segment from third aortic arch, ascending intrapetrous segment from second and third aortic arch; horizontal petrous segment from first and second aortic arch, ascending segment in foramen lacerum from first aortic arch and primitive maxillary artery; horizontal segment of carotid siphon from primitive maxillary artery and dorsal ophthalmic artery; clinoid segment from dorsal and ventral ophthalmic artery; and finally terminal segment from
CONGENITAL ABSENCE OR HYPOPLASIA
345
Fig 4. Bilateral hypoplasia of the ICA. (A) Angiographic view of the arcus aorta shows that both CCA have smaller caliper than the vertebral arteries. Selective (B) right and (C) left CCA angiograms show that both hypoplastic ICAs go to the cavernous segment and form the intercavernous, parasellar collateral networks. (D) Axial supratentorial contrast enhanced computed tomography scan of the brain shows hypertrophic parasellar collateral pathways and communicans with bilateral PCA via posterior communicant artery. (E) Frontal view from the right vertebral arteriography displays collateral flows to both MCA and ACA with parasellar collateral pathways.
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Fig 5. Right carotid angiography shows the branches of the external carotid artery, and there is no evidence of the right ICA (agenesis of the right ICA).
primitive ophthalmic artery and anterior cerebral artery. Lack of development of one or more of those branches may eventually lead to poor formation of the carotid system. CCA arising from aortic sac may explain the conjugation of left CCA with brachiocephalic truncus in case 6. Some authors indicate the common embryological origin from the third aortic arch. However, it is reasonable to assume that the external and internal carotid arteries have separate origins because they have separate stemming from the aortic sac and ECA rarely disappears in the absence of ICA. Collateral vessels may appear instead of different segments of ICA.23-26 There is no clear relation between the severity of cerebral ischemia and ICA absence and hypoplasia. However, development of collateral vessels, flow direction change in the circle of Willis and increased blood flow in vertebrobasilar system or contralateral anterior circulation provides additional supply for the involved area. However, it seems in this series that blood flow from ECA anastomoses do not contribute significantly for this compensation. Particularly in patients with bilateral ICA hypoplasia, arteriosclerosis and stenosis of compensating vessels because of cervical spondylolysis in advanced ages may lead to more prominent and severe consequences.18,26 If there is a possibility of cerebral infarct or occlusion of cerebral vessels MRI, MRA, and CT angiography should be included in evaluation of those patients.
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Diffusion- and perfusion-weighted sequences should be added in search of acute, subacute infarction for a patient with absent or hypoplastic ICA.27-29 Conventional MRI is normal in case 7. Left CCA was evident but ICA could not be visualized. Skull-base CT showed small bony carotid canal consistent with ICA hypoplasia. Aortic arch maldevelopment reminds other possible vascular abnormalities in case 6. Hematoma secondary to rupture of aneurysm of MCA was present. In cases with bilateral ICA hypoplasia or absence (cases 2 and 3), ICAs were small in diameter at the carotid siphon and vertebral arteries were prominent in the patient with bilaterally hypoplastic ICA. There was no other developmental abnormality.9,22,28,30,31 Concentric stenosis of ICA lumen may develop secondary to different acquired pathologies like arteriosclerosis, arteritis, fibromuscular dysplasia, intimal dissection, or Moya Moya disease.29 High-level stenosis of ICA at the origin of the vessel, accentuated vasospasm, acute occlusion of distal ICA, or increased intracranial pressure may be called as “functional stenosis” and show similar imaging findings. These acquired causes will be excluded by demonstrating decreased bony carotid canal caliber, clinical follow-up, and/or diffusion-perfusion MR images, which indicate normal regional cerebral blood flow.27,32 Hypoplastic ICA may be confused with an enlarged ascending pharyngeal artery in the presence of occlusion or agenesis of cervical part of ICA. Catheter angiography helps in differential diagnosis, which is very important in treatment planning of acquired stenosis of ICA. Clinical findings and CT and MRI images are also helpful. Patients with congenital absence of ICA have no symptoms in terms of cerebral ischemia. However, rupture of an aneurysm or acquired extra-intraluminal diseases leading to ischemic symptoms may need endarterectomy or anticoagulation therapies when ipsilateral ICA dysgenesis is present.18,23,33 The outer diameter of the vessel is normal, but the wall thickness has been increased in acquired luminal stenosis like Takayasu arteritis. However, arterial lumen, diameter of the vessel, and the wall thickness has been decreased in ICA hypoplasia. Wall thickness of the vessel is normal in case of “functional stenosis,” which results from in-
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347
Fig 6. Hypogenesis of the left ICA. (A) Anterioposterior and oblique views of the MRA with 3-dimensional time of fight technique show hypertrophic vertebrobasilar system and right carotid artery system. (B) No abnormality is seen on the proton density scan of the supratenterorial region of the brain. (C) Bone image of the skull base. CT of the skull base reveals normal right carotid canal (C) and hypoplastic left (D) carotid canal.
sufficient volume because of decreased vessel lumen. Color Doppler ultrasonography (CDUS) provides adequate evaluation of the carotid artery stenosis. MR has an advantage to show vessel wall disease and dissection better than CDUS because it has better contrast resolution (though worse spatial resolution) than CDUS. Advances of techniques and improvement in
spatial resolution in MRI and CT will be able to delineate arterial diseases in the future.34,35 Ipsilateral decrease in diameter of CCA supports the theory of congenital etiology. CDUS and US examinations may reveal some abnormalities like hypoechoic plaques, thrombus, and parietal hematoma. CDUS may also show the level of stenosis and the degree of obstruc-
348
tion. Well-known disadvantages of CDUS and US are inability to evaluate distal vascular regions like deep cervical, petrous, and intracranial parts. Vascular imaging on MRA depends on T1 shortening despite intravascular flow of contrast media. It’s easy to display maximum intensity projection (MIP) images of vascular structures between aortic arch and Willis circle, which is very similar to DSA images. Disadvantages of MIP images are omitting arterial stenoses because jugular vein flow may overlap because of worse temporal resolution. Sparing of the first part of ICA had been described as a sign of dysgenesis by some authors.3,16,22,27,29 There are 2 cases with this type of involvement in our series. DSA and MRA may not show parietal sources because they cannot delineate vessel walls. Collateral blood flow to intracranial vessels may come from contralateral ICA or from vertebrobasilar system through the circle of Willis. Persistent trigeminal arteries, persistent tympanic or stapedial arteries, hypoglossal artery, intercavernous anastomosis, ophthalmic arteries, branches and anastomoses of ECA, and rete mirabilis were described as other collateral pathways.10,12,13,14,18 It has been observed in this study that the vertebrobasilar system is the main collateral pathway in patients with bilaterally hypoplastic or absent ICA. There were no other embryological or acquired collaterals. In previous reports, presence of collaterals may be the sign of a coexistent vascular occlusion or stenosis in vertebrobasilar artery, which diminish the delivery of blood flow to the agenesis side. Such collaterals may appear rapidly even in temporary occlusion of ipsilateral carotid arteries by balloon catheter. ICA hypoplasia or absence always accompanies with a small and/or absent carotid canal. Development of ICA is completed at the forth embryonic week, and the bony canal is formed at fifth and sixth embryonic weeks. Demonstration of a small carotid canal by CT is helpful for excluding acquired etiologies.36,37 Skull-base CT showed at least 2 times smaller diameter of the carotid canal in 5 cases (cases 2, 3, 5, 6, and 7). Upper and lower limits of the diameter of the carotid canal in petrous bone were reported to be 4 to 7.5 mm for the vertical part and 4.5 to 7 mm for the horizontal part by Lenonetti et al.38 All
TAS¸ AR ET AL
cases in this study had less than 4 mm in diameter. Patients with ICA dysplasia should be evaluated for a possible intracranial aneurysm of the circle of Willis because the incidence of aneurysm was found to be 24% to 34% in those patients compared with 2% to 4% in normal population. Increased hemodynamic pressure in the collateral arteries of the dysplastic vessels is known to cause the aneurysms. CT, MRI, and MRA always have to be included in the radiologic agenda of the clinician for imaging of those vessels. In conclusion, hypoplasia or absence of ICA (agenesis or aplasia) is a rare abnormality. Combined use of MRI, MRA, and CT scanning of the skull base and head may disclose small but patent ICA. Collateral vessels seem to be usual in such cases, but they may be prominent in case of acquired vascular occlusion or increased hemodynamic pressure in dysplastic changes in collateral arteries are known causes of aneurysms. The main vascular supply for the brain in patients with congenitally small or absent ICA is the vertebrobasillar system in bilateral cases. However, contralateral carotid vessel is the dominant arterial supply for unilateral cases, which has to be kept in mind in surgical interventions to the involved side. REFERENCES 1. Cali RL, Berg R, Rama K: Bilateral internal carotid artery agenesis: A case study and review of the literature. Surgery 113:227-233, 1993 2. Quint DJ, Silbergleit R, Young WC: Absence of the carotid canals at skull base CT. Radiology 182:477-481, 1992 3. Pilleul F, Guibaud L, Badinand N, et al: Bilateral internal carotid agenesis: Value of CT angiography and correlation to embryogenesis. Eur Radiol 11:858-860, 2001 4. Sunada I, Inoue T: Bilateral internal carotid artery agenesis. J Neurol Neurosurg Psychiatry 61:206-207, 1996 5. Ide C, De Coene B, Mailleux P, et al: Hypoplasia of the internal carotid artery: A noninvasive diagnosis. Eur Radiol 10:1865-1870, 2000 6. Sliwka U, Schmith P, Reul J, et al: Agenesis of the internal carotid artery: Color Doppler, CT and MR angiography findings. J Clin Ultrasound 26:213-216, 1998 7. Handa J, Matsuda I, Nakasu S, et al: Agenesis of an internal carotid artery: Angiographic, tomographic and computed tomographic correlation. Neuroradiology 19: 207-211, 1980 8. Florio F, Balzano S, Nardella M, et al: Congenital absence of the internal carotid artery. Cardiovasc Intervent Radiol 22:74-78, 1999 9. Claros P, Bandos R, Gilea I, et al: Major congenital anomalies of the internal carotid artery: Agenesis, aplasia
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and hypoplasia. Int J Pediatr Otorhinolaryngol 49:69-76, 1999 10. Teal JS, Rumbaugh CL, Bergeron RT, et al: Congenital absence of the internal carotid artery associated with cerebral hemiatrophy, absence of the external carotid artery, and persistence of the stapedial artery. AJR Am J Roentgenol 118:534-544, 1973 11. Mellado JM, Merino X, Ramos A, et al: Agenesis of the internal carotid artery with a trans-sellar anastomosis: CT and MRI findings in late-onset congenital hypopituitarism. Neuroradiology 43:237-241, 2001 12. Damry N, Hanquinet S, Christophe C, et al: Bilateral congenital absence of the internal carotid artery with a primitive transmaxillary arterial anastomosis. Pediatr Radiol 24:200-203, 1994 13. Verbist B, Hermans R, Devlies F, et al: Quiz case of the month. Partial agenesis of the internal carotid artery with collateral circulation through an enlarged inferior tympanic artery. Eur Radiol 6:939-940, 1996 14. Hattori T, Kobayashi H, Inoue S, et al: Persistent primitive trigeminal artery associated with absence of the internal carotid artery. Surg Neurol 50:352-355, 1998 15. Quint DJ, Silbergleit R, Young WC: Absence of the carotid canals at skull base CT. Radiology 182:477-481, 1992 16. Given AC, Hellinger HF, Baker DM, et al: Congenital absence of the internal carotid artery: Case reports and review of the collateral circulation. AJNR Am J Neuroradiol 22:1953-1959, 2001 17. Iaccarino V, Tedeschi E, Brunetti A, et al: Congenital agenesis/aplasia of the internal carotid arteries: MRA and SPECT findings. J Comput Assist Tomogr 19:987-990, 1995 18. Midkiff RB, Boykin MW, McFarland DR, et al: Agenesis of the internal carotid artery with intercavernous anastomosis. AJNR Am J Neuroradiol 16:1356-1359, 1995 19. Afifi AK, Godersky JC, Menezes A, et al. Cerebral hemiatrophy, hypoplasia of internal carotid artery and intracranial aneurysms: A rare association occurring in an infant. Arch Neurol 44:232-235, 1987 20. Chen MC, Liu HM, Huang KM: Agenesis of the internal carotid artery associated with neurofibromatosis type II. AJNR Am J Neuroradiol 15:1184-1186, 1994 21. Teal IS, Naheedy MH, Hasso AN: Total agenesis of the internal carotid artery. AJNR Am J Neuroradiol 1:435442, 1980 22. Lasjaunias P, Santoyo-Vazquez A: Segmental agenesis of the internal carotid artery: angiographic aspects with embryological discussion. Anat Clin 6:133-141, 1984
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23. Takahashi S, Higano S, Kurihara N, et al: Congenital absence and aberrant course of the internal carotid artery. Eur Radiol 6:650-654, 1996 24. Heth JA, Loftus CM, Piper JG, et al: Hypoplastic internal carotid artery mimicking a classic angiographic “string sign.” J Neurosurg 86:567-570, 1997 25. Schaefer PW, Grant PE, Gonzales RG: Diffusionweighted MR Imaging of the brain. Radiology 217:331345, 2000 26. Petrella JR, Provenzale JM: MR perfusion imaging of the brain: Techniques and applications. AJR Am J Roentgenol 175:207-219, 2000 27. Meder JF, Blustajn J, Trystram D, et al: Radiologic anatomy of segmental agenesis of the internal carotid artery. Surg Radiol Anat 19:385-394, 1997 28. Graham CB, Wippold FJ, Capps GW: Magnetic resonance imaging in internal carotid artery agenesis with computed tomography and angiographic correlation— Case reports. Angiology 50:847-853, 1999 29. Cali RL, Berg R, Rama K: Bilateral internal carotid artery agenesis: A case study and review of the literature. Surgery 113:227-233, 1993 30. Czarnecki EJ, Silbergleit R, Mehta BA, et al: Absence of the supraclinoid internal carotid artery in association with intracranial aneurysms. Neuroradiology 40: 11-14, 1998 31. Harps E, Helmke K: Diagnosis of congenital absence of internal carotid artery by power angio sonography. Eur Radiol 8:1245-1247, 1998 32. Breidahl WH, Khanguhj MS: Case report: MRI diagnosis of congenital absence of the internal carotid artery. Clin Radiol 42:354-355, 1990 33. David H, Dubayle P, Girodeau A, et al: Agenesis of the internal carotid artery: Two cases report. J Radiol 81:147-150, 2000 34. Kane AG, William PD, Barkovich J, et al: Reduced caliber of the internal carotid artery: A normal finding with ipsilateral absence or hypoplasia of the A1 segment. AJNR Am J Neuroradiol 17:1295-1301, 1996 35. Jordan JA, Lewis M, Rollins N, et al: Congenital internal carotid artery aneurysm with absence of the petrous portion of the contralateral internal carotid artery. Ann Otol Rhinol Laryngol 109:1167-1169, 2000 36. Nezu N, Ninchoji T, Kitanaka H, et al: A case of congenital absence of the left internal carotid artery. Comput Radiol 8:355-360, 1984 37. Murotani K, Hiramoto M: Agenesis of the internal carotid artery with a large hemangioma of the tongue. Neuroradiology 27:357-359, 1985 38. Wang PJ, Liu HM, Young C, et al: Agenesis of internal carotid artery associated with symptomatic partial epilepsy. Epilepsia 35:1337-1341, 1994
Congenital absence (agenesis, aplasia) or hypoplasia of one or both internal carotid arteries (ICAs) is a rare developmental abnormality and is discovered incidentally by color Doppler carotid sonography, angiography, computed tomography (CT), or mag-
From the Departments of *Radiology; †ENT; ‡Pediatrics; and §Neurosurgery, Ankara Hospital of Ministry of Health, Ankara, Turkey. Address correspondence to: Mustafa Tasar, MD, Gu¨lhane Medical School, Department of ORL & HNS, 06018 Etlik, Ankara, Turkey. E-mail: [email protected]. © 2004 Elsevier Inc. All rights reserved. 0196-0709/$ - see front matter doi:10.1016/j.amjoto.2004.04.008
netic resonance imaging (MRI) of the head and neck taken for some other reason.1-3 The incidence of the absence of ICA has been reported to be around 0.01%.4-7 The term of the absence of carotid artery has been substituted for the agenesis, aplasia, or hypoplasia of the ICA, which may lead to some misunderstanding because the descriptive classification of this anomaly is lacking.8 It should be kept in mind that the term of hypoplasia here means the underdeveloped carotid with small caliber. These developmental anomalies of ICA are strongly suggested when the carotid canal is absent or hypoplasic as seen on CT scanning of the skull base.2,6,9 Absence of blood flow in the
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carotid because of absence of vessel lumen should be confirmed by angiography. Most patients are not symptomatic because of sufficient cerebral circulation supplied to the defective area by the communicating arteries of the circle of Willis, intercavernous anastomosis, communicating arteries from external carotid artery, and by persistent embryologic arteries to the carotid artery territory.10-17 They live for years without any symptom. However, in some patients, symptoms related with cerebral ischemia because of less blood flow can occur and enlargement of collateral vessels may lead to associated intracranial aneurysm with obvious problems.18,19 It is important to realize the clinical characteristics, imaging features, and surgical implications of this entity because coexisting symptoms may lead the patients to have invasive and risky interventions. The aim of this study is to emphasize the characteristic radiologic and clinical picture in patients with absence or hypoplasia of carotid artery, to delineate the associated abnormalities and existing collateral vessels, and to find out its incidence. MATERIALS AND METHODS Five thousand one hundred cerebral MRI and/or catheter angiograms performed between February 1988 and March 2002 in our department were reviewed and 7 patients with congenital absence or hypoplasia of ICA (5 unilateral and 2 bilateral) were identified. Of all 5 patients, 2 were with absence and 3 were with hypoplasia of ICA; of 2 bilateral cases, one was presented with bilateral absence and the other was presented with hypoplasia. All cases were documented clinically and radiologically by conventional MRI or by other magnetic resonance angiography (MRA) techniques. One bilateral and 4 unilateral absences of ICA were also examined by digital subtraction angiography (DSA). Two bilateral and 4 unilateral cases were also examined by color Doppler ultrasonography. All patients were examined by 1.5 T MR systems (Magnetom SP 63 or Magnetom Vision Plus, Siemens, Erlengen, Germany). Axial T1-weighted and T2-weighted (spin echo proton density, turbo spin echo, and fluid attenuated inversion recovery) sequences were obtained with head coil in supine position. Diffusion-weighted images (b0, b500, b1000 s/mm2) were obtained from 3 patients to exclude acute ischemic lesions and apparent diffusion coefficient maps created (after 1999). The clinical and radiologic data of the patients are shown in Table 1.
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Super selective catheterization (Digitron II and Multistar Plus, Erlengen, Germany) of both internal and external carotid and vertebral arteries were performed under local anesthesia via femoral artery. Two different CT scanners were used for brain imaging including the skull base and the temporal bone with 2-mm slice thickness (Somotom DRH, Siemens, Erlengen, Germany and GE Hi-Speed Advantage, General Electric, Milwaukee, WI). CT angiograms were also obtained with spiral CT scanner. Skull base and the bony carotid canal were assessed on each CT image. If the bony carotid canal was not visible at the serial cuts of the base of the skull, then this abnormality was defined as the absence of the carotid canal and carotid artery. If the bony canal was present, the diameter of the pathological side was compared with that of contralateral part. In suspected bilateral cases, diameter of the canal was compared with that of normal side in patients with unilateral ICA hypoplasia. If the diameter was less than half of the size of normal, then it was accepted as abnormal. However, the patency of the abnormal artery was always controlled with the angiography. In cases with absent ICA, the presence of collateral vessels and other clinical and radiological abnormalities were investigated. Color Doppler sonography was performed with 2 different devices (Acuson XP/10 and Toshiba SS270 A, Tokyo, Japan). B-mode and pulsed-wave color Doppler images were obtained through both common and ICAs, and then blood flow velocity measurements were made.
RESULTS Three of 5 patients with unilateral agenesis or hypoplasia and 2 patients with bilateral absence or hypoplasia were male. The common symptom for all patients was headache. CT revealed intracerebral and subarachnoid hemorrhage in 1 patient with brief and sudden loss of consciousness and in another one with a history of pituitary hypogonadism and chronic headache. Ruptured left middle cerebral artery (MCA) aneurysm and aortic arch abnormality, which was presumably related to the patient’s headache in both patients, was shown. It was revealed that the left common carotid artery and brachiocephalic trunk was running very close to each other as if a single vessel (case 6) (Fig 1). Unilateral absence (agenesis) of the ICA was considered as the probable cause of the hypogonadism. In 1 patient (left hypoplasia) with spontaneous epistaxis from time to time in addition to the headache, CT and DSA revealed nasopharyngeal intense enhancing mass consistent with the angiofibroma (case 7) (Fig 2).
Patient No. Age/Sex
Presenting Complaints
CDUS and US
CT
Diffusion- and Perfusion-weighted Abnormality MR MRA MRI DSA Side
Type of Abnormality
Main Collateral Flow
Associated Abnormalities
⫹
⫹
N
⫺
Left
Hypoplasia
PCOM ACOM
⫺
⫹
⫹
⫺
⫹
Bilateral
Hypoplasia
PCOM ACOM intercavernous anastomoses
⫺
⫺
⫹
⫹
N
⫺
Bilateral
⫹
⫹
⫺
⫹
Right
Hypoplastic bony carotid canal Hypoplastic CCA intracerebral/ subarachnoid hemorrhage
⫹
⫹
N
⫹
Left
PCOM ACOM ACOM PCOM ACOM PCOM
⫺
⫺
Absence (agenesis) Absence (agenesis) Hypoplasia
⫹
⫹
⫺
⫹
Left
Absence of ACOM ICA and PCOM hypoplastic CCA
Small CCA Left hypoplastic and bony carotid hypoplastic canal ICA
⫹
⫹
⫺
⫹
Left
ACOM PCOM
1
53/M
Headache
NA
2
25/M
Headache
3
57/M
Headache
4
17/F
5
55/F
Headache, syncope Headache
Bilateral small CCA and cervical ICA Bilateral small CCA ⫺
6
17/M
Headache, Hypoplastic loss of CCA and conciousness absenct ICA
7
21/M
Headache, episodic nose bleeding
ICA absent
Hypoplastic bony carotid canal Bilateral hypoplastic carotid canal
hypoplasia
CONGENITAL ABSENCE OR HYPOPLASIA
TABLE 1. Clinical and Radiologic Findings of the Patients
⫺ ⫺
Arcus aorta abnormality, primary hypogonadism, noduler goitre, left intracerebral hematoma Nasopharynx angiofibroma
Abbreviations: N, normal; CCA, common carotid artery; ICA, internal carotid artery; US, ultrasonography; CDUS, color Doppler ultrasonography; M, male; F, female; ACOM, anterior communicant artery; PCOM, posterior communicant artery.
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Fig 1. Left ICA agenesis in a patient with hypogonodism, anomaly of the arcus aorta, and the ruptured aneurysm. (A) Digital subtruction angiography of the arcus aorta. Brachiosephalic trunk, thin left CCA and left subclavian artery are running very close to each other. Note that left CCA is thinner than right ICA. (B) Selective left CCA angiography shows marked left ECA and absence of the left ICA. (C) Left CCA is smaller than right CCA as seen on the axial contrast enhanced computed tomography of the neck.
Color Doppler sonography and angiography showed small caliber of CCA in 2 bilateral cases (cases 2 and 3) (Figs 3 and 4). CCA continued as the external carotid artery and no ICA was present in 3 of 4 patients with unilateral carotid abnormality (2 hypoplasia, 1 absence) (cases 5, 6, and 7). Skull base and temporal bone CT scans revealed significantly narrow carotid canal in 1 patient with bilateral hypoplasia of ICA. Carotid canal was also very small in 3 patients with unilateral hypoplasia. One patient with unilateral agenesis could not be scanned with CT (case 4) and angiography revealed the entity
(Fig 5). Although left intracerebral hematoma with subarachnoid hemorrhage was evident in 1 of 6 patients examined by CT (case 6) (Fig 1), brain CT images of other 5 cases were normal. MRA images were in well accordance with DSA images. Diffusion images in 2 patients with leftsided agenesis were unremarkable (cases 5 and 7) (Fig 6). DISCUSSION ICA is one of the most stable arteries of the human body. It rarely shows abnormal devel-
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Fig 2. Left ICA hypoplasia in a patient with nasopharyngeal angiofibroma. (A) Arcus aorta angiography shows hypoplasic left CCA and hypertrophic left vertebral artery. (B) Selective left CCA angiography reveals a staining nasopharyngeal mass and complete absence of left ICA. (C) Axial contrast enhanced computed tomography scan of the neck shows large caliper right CCA and left vertebral artery and left CCA with small caliper. (D) Axial noncontrasted computed tomography of the skull base with bone windowing reveals hypoplasic left carotid canal (arrowhead).
opment. Tode reported the first case of ICA agenesis in 1787, which was accidentally encountered after a cadaveric dissection.11,20 The prevalence of congenital absence of ICA is estimated as 0.01%.18,21 The prevalence of absence of ICA is 0.058% and the prevalence of hypoplasia of ICA is 0.079% in our series. Unilateral absence or hypoplasia of ICA is more frequent on the left and bilateral absence or hypoplasia is more exceptional and reported to be less than 10% of unilateral involvement. On the other hand, it is one of the
major concerns that the reported incidences are likely not to be realistic because there seems to be some confusion in terminology. It is better to classify dysgenesis of the carotid artery in 3 subgroups as agenesis, aplasia, and hypoplasia. ICA with small caliber and patent lumen corresponds to hypoplasia. Aplasia indicates a vascular remnant, which has no vascular formation. The etiology of agenesis, aplasia, and hypoplasia of ICA is still unknown. There are conflicting proposals for the maldevelopment
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Fig 3. Bilateral ICA agenesis in a patient with no other radiologic finding and clinical symptom. (A) MRA with the 3-dimensional time of flight technique. The anteroposterior projection of MRA shows the extremely tortuous and hypertrophic vertebrobasilar system and absence of both ICA. (B) Axial contrast enhanced computed tomography (CECT) scan of the posterior fossa shows hypertrofic and tortuous vertebrobasilar system. (C) Axial CECT scan of the supratentorial region of the brain shows collateral supply to both cerebral hemisphere via hypertrophic posterior communicant artery and parasellar anostomotic collateral vessels. (D) Axial noncontrast computed tomography scans of the skull base shows both hypoplastic carotid canals.
of this artery. One of the theories indicates a secondary regression of the ICA from the beginning of the intrauterine life. However, the other one claims interruption of the development of the artery for unknown causes after a period of normal growth, which may justify the difference between the loss of maturity in some and absence of the artery in others. Lasjaunias and Santoyo-Vazquez22 have indicated that 7 different embryological segment branches come together and forms the internal
carotid artery system. Those are cervical segment from third aortic arch, ascending intrapetrous segment from second and third aortic arch; horizontal petrous segment from first and second aortic arch, ascending segment in foramen lacerum from first aortic arch and primitive maxillary artery; horizontal segment of carotid siphon from primitive maxillary artery and dorsal ophthalmic artery; clinoid segment from dorsal and ventral ophthalmic artery; and finally terminal segment from
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Fig 4. Bilateral hypoplasia of the ICA. (A) Angiographic view of the arcus aorta shows that both CCA have smaller caliper than the vertebral arteries. Selective (B) right and (C) left CCA angiograms show that both hypoplastic ICAs go to the cavernous segment and form the intercavernous, parasellar collateral networks. (D) Axial supratentorial contrast enhanced computed tomography scan of the brain shows hypertrophic parasellar collateral pathways and communicans with bilateral PCA via posterior communicant artery. (E) Frontal view from the right vertebral arteriography displays collateral flows to both MCA and ACA with parasellar collateral pathways.
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Fig 5. Right carotid angiography shows the branches of the external carotid artery, and there is no evidence of the right ICA (agenesis of the right ICA).
primitive ophthalmic artery and anterior cerebral artery. Lack of development of one or more of those branches may eventually lead to poor formation of the carotid system. CCA arising from aortic sac may explain the conjugation of left CCA with brachiocephalic truncus in case 6. Some authors indicate the common embryological origin from the third aortic arch. However, it is reasonable to assume that the external and internal carotid arteries have separate origins because they have separate stemming from the aortic sac and ECA rarely disappears in the absence of ICA. Collateral vessels may appear instead of different segments of ICA.23-26 There is no clear relation between the severity of cerebral ischemia and ICA absence and hypoplasia. However, development of collateral vessels, flow direction change in the circle of Willis and increased blood flow in vertebrobasilar system or contralateral anterior circulation provides additional supply for the involved area. However, it seems in this series that blood flow from ECA anastomoses do not contribute significantly for this compensation. Particularly in patients with bilateral ICA hypoplasia, arteriosclerosis and stenosis of compensating vessels because of cervical spondylolysis in advanced ages may lead to more prominent and severe consequences.18,26 If there is a possibility of cerebral infarct or occlusion of cerebral vessels MRI, MRA, and CT angiography should be included in evaluation of those patients.
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Diffusion- and perfusion-weighted sequences should be added in search of acute, subacute infarction for a patient with absent or hypoplastic ICA.27-29 Conventional MRI is normal in case 7. Left CCA was evident but ICA could not be visualized. Skull-base CT showed small bony carotid canal consistent with ICA hypoplasia. Aortic arch maldevelopment reminds other possible vascular abnormalities in case 6. Hematoma secondary to rupture of aneurysm of MCA was present. In cases with bilateral ICA hypoplasia or absence (cases 2 and 3), ICAs were small in diameter at the carotid siphon and vertebral arteries were prominent in the patient with bilaterally hypoplastic ICA. There was no other developmental abnormality.9,22,28,30,31 Concentric stenosis of ICA lumen may develop secondary to different acquired pathologies like arteriosclerosis, arteritis, fibromuscular dysplasia, intimal dissection, or Moya Moya disease.29 High-level stenosis of ICA at the origin of the vessel, accentuated vasospasm, acute occlusion of distal ICA, or increased intracranial pressure may be called as “functional stenosis” and show similar imaging findings. These acquired causes will be excluded by demonstrating decreased bony carotid canal caliber, clinical follow-up, and/or diffusion-perfusion MR images, which indicate normal regional cerebral blood flow.27,32 Hypoplastic ICA may be confused with an enlarged ascending pharyngeal artery in the presence of occlusion or agenesis of cervical part of ICA. Catheter angiography helps in differential diagnosis, which is very important in treatment planning of acquired stenosis of ICA. Clinical findings and CT and MRI images are also helpful. Patients with congenital absence of ICA have no symptoms in terms of cerebral ischemia. However, rupture of an aneurysm or acquired extra-intraluminal diseases leading to ischemic symptoms may need endarterectomy or anticoagulation therapies when ipsilateral ICA dysgenesis is present.18,23,33 The outer diameter of the vessel is normal, but the wall thickness has been increased in acquired luminal stenosis like Takayasu arteritis. However, arterial lumen, diameter of the vessel, and the wall thickness has been decreased in ICA hypoplasia. Wall thickness of the vessel is normal in case of “functional stenosis,” which results from in-
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Fig 6. Hypogenesis of the left ICA. (A) Anterioposterior and oblique views of the MRA with 3-dimensional time of fight technique show hypertrophic vertebrobasilar system and right carotid artery system. (B) No abnormality is seen on the proton density scan of the supratenterorial region of the brain. (C) Bone image of the skull base. CT of the skull base reveals normal right carotid canal (C) and hypoplastic left (D) carotid canal.
sufficient volume because of decreased vessel lumen. Color Doppler ultrasonography (CDUS) provides adequate evaluation of the carotid artery stenosis. MR has an advantage to show vessel wall disease and dissection better than CDUS because it has better contrast resolution (though worse spatial resolution) than CDUS. Advances of techniques and improvement in
spatial resolution in MRI and CT will be able to delineate arterial diseases in the future.34,35 Ipsilateral decrease in diameter of CCA supports the theory of congenital etiology. CDUS and US examinations may reveal some abnormalities like hypoechoic plaques, thrombus, and parietal hematoma. CDUS may also show the level of stenosis and the degree of obstruc-
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tion. Well-known disadvantages of CDUS and US are inability to evaluate distal vascular regions like deep cervical, petrous, and intracranial parts. Vascular imaging on MRA depends on T1 shortening despite intravascular flow of contrast media. It’s easy to display maximum intensity projection (MIP) images of vascular structures between aortic arch and Willis circle, which is very similar to DSA images. Disadvantages of MIP images are omitting arterial stenoses because jugular vein flow may overlap because of worse temporal resolution. Sparing of the first part of ICA had been described as a sign of dysgenesis by some authors.3,16,22,27,29 There are 2 cases with this type of involvement in our series. DSA and MRA may not show parietal sources because they cannot delineate vessel walls. Collateral blood flow to intracranial vessels may come from contralateral ICA or from vertebrobasilar system through the circle of Willis. Persistent trigeminal arteries, persistent tympanic or stapedial arteries, hypoglossal artery, intercavernous anastomosis, ophthalmic arteries, branches and anastomoses of ECA, and rete mirabilis were described as other collateral pathways.10,12,13,14,18 It has been observed in this study that the vertebrobasilar system is the main collateral pathway in patients with bilaterally hypoplastic or absent ICA. There were no other embryological or acquired collaterals. In previous reports, presence of collaterals may be the sign of a coexistent vascular occlusion or stenosis in vertebrobasilar artery, which diminish the delivery of blood flow to the agenesis side. Such collaterals may appear rapidly even in temporary occlusion of ipsilateral carotid arteries by balloon catheter. ICA hypoplasia or absence always accompanies with a small and/or absent carotid canal. Development of ICA is completed at the forth embryonic week, and the bony canal is formed at fifth and sixth embryonic weeks. Demonstration of a small carotid canal by CT is helpful for excluding acquired etiologies.36,37 Skull-base CT showed at least 2 times smaller diameter of the carotid canal in 5 cases (cases 2, 3, 5, 6, and 7). Upper and lower limits of the diameter of the carotid canal in petrous bone were reported to be 4 to 7.5 mm for the vertical part and 4.5 to 7 mm for the horizontal part by Lenonetti et al.38 All
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cases in this study had less than 4 mm in diameter. Patients with ICA dysplasia should be evaluated for a possible intracranial aneurysm of the circle of Willis because the incidence of aneurysm was found to be 24% to 34% in those patients compared with 2% to 4% in normal population. Increased hemodynamic pressure in the collateral arteries of the dysplastic vessels is known to cause the aneurysms. CT, MRI, and MRA always have to be included in the radiologic agenda of the clinician for imaging of those vessels. In conclusion, hypoplasia or absence of ICA (agenesis or aplasia) is a rare abnormality. Combined use of MRI, MRA, and CT scanning of the skull base and head may disclose small but patent ICA. Collateral vessels seem to be usual in such cases, but they may be prominent in case of acquired vascular occlusion or increased hemodynamic pressure in dysplastic changes in collateral arteries are known causes of aneurysms. The main vascular supply for the brain in patients with congenitally small or absent ICA is the vertebrobasillar system in bilateral cases. However, contralateral carotid vessel is the dominant arterial supply for unilateral cases, which has to be kept in mind in surgical interventions to the involved side. REFERENCES 1. Cali RL, Berg R, Rama K: Bilateral internal carotid artery agenesis: A case study and review of the literature. Surgery 113:227-233, 1993 2. Quint DJ, Silbergleit R, Young WC: Absence of the carotid canals at skull base CT. Radiology 182:477-481, 1992 3. Pilleul F, Guibaud L, Badinand N, et al: Bilateral internal carotid agenesis: Value of CT angiography and correlation to embryogenesis. Eur Radiol 11:858-860, 2001 4. Sunada I, Inoue T: Bilateral internal carotid artery agenesis. J Neurol Neurosurg Psychiatry 61:206-207, 1996 5. Ide C, De Coene B, Mailleux P, et al: Hypoplasia of the internal carotid artery: A noninvasive diagnosis. Eur Radiol 10:1865-1870, 2000 6. Sliwka U, Schmith P, Reul J, et al: Agenesis of the internal carotid artery: Color Doppler, CT and MR angiography findings. J Clin Ultrasound 26:213-216, 1998 7. Handa J, Matsuda I, Nakasu S, et al: Agenesis of an internal carotid artery: Angiographic, tomographic and computed tomographic correlation. Neuroradiology 19: 207-211, 1980 8. Florio F, Balzano S, Nardella M, et al: Congenital absence of the internal carotid artery. Cardiovasc Intervent Radiol 22:74-78, 1999 9. Claros P, Bandos R, Gilea I, et al: Major congenital anomalies of the internal carotid artery: Agenesis, aplasia
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and hypoplasia. Int J Pediatr Otorhinolaryngol 49:69-76, 1999 10. Teal JS, Rumbaugh CL, Bergeron RT, et al: Congenital absence of the internal carotid artery associated with cerebral hemiatrophy, absence of the external carotid artery, and persistence of the stapedial artery. AJR Am J Roentgenol 118:534-544, 1973 11. Mellado JM, Merino X, Ramos A, et al: Agenesis of the internal carotid artery with a trans-sellar anastomosis: CT and MRI findings in late-onset congenital hypopituitarism. Neuroradiology 43:237-241, 2001 12. Damry N, Hanquinet S, Christophe C, et al: Bilateral congenital absence of the internal carotid artery with a primitive transmaxillary arterial anastomosis. Pediatr Radiol 24:200-203, 1994 13. Verbist B, Hermans R, Devlies F, et al: Quiz case of the month. Partial agenesis of the internal carotid artery with collateral circulation through an enlarged inferior tympanic artery. Eur Radiol 6:939-940, 1996 14. Hattori T, Kobayashi H, Inoue S, et al: Persistent primitive trigeminal artery associated with absence of the internal carotid artery. Surg Neurol 50:352-355, 1998 15. Quint DJ, Silbergleit R, Young WC: Absence of the carotid canals at skull base CT. Radiology 182:477-481, 1992 16. Given AC, Hellinger HF, Baker DM, et al: Congenital absence of the internal carotid artery: Case reports and review of the collateral circulation. AJNR Am J Neuroradiol 22:1953-1959, 2001 17. Iaccarino V, Tedeschi E, Brunetti A, et al: Congenital agenesis/aplasia of the internal carotid arteries: MRA and SPECT findings. J Comput Assist Tomogr 19:987-990, 1995 18. Midkiff RB, Boykin MW, McFarland DR, et al: Agenesis of the internal carotid artery with intercavernous anastomosis. AJNR Am J Neuroradiol 16:1356-1359, 1995 19. Afifi AK, Godersky JC, Menezes A, et al. Cerebral hemiatrophy, hypoplasia of internal carotid artery and intracranial aneurysms: A rare association occurring in an infant. Arch Neurol 44:232-235, 1987 20. Chen MC, Liu HM, Huang KM: Agenesis of the internal carotid artery associated with neurofibromatosis type II. AJNR Am J Neuroradiol 15:1184-1186, 1994 21. Teal IS, Naheedy MH, Hasso AN: Total agenesis of the internal carotid artery. AJNR Am J Neuroradiol 1:435442, 1980 22. Lasjaunias P, Santoyo-Vazquez A: Segmental agenesis of the internal carotid artery: angiographic aspects with embryological discussion. Anat Clin 6:133-141, 1984
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23. Takahashi S, Higano S, Kurihara N, et al: Congenital absence and aberrant course of the internal carotid artery. Eur Radiol 6:650-654, 1996 24. Heth JA, Loftus CM, Piper JG, et al: Hypoplastic internal carotid artery mimicking a classic angiographic “string sign.” J Neurosurg 86:567-570, 1997 25. Schaefer PW, Grant PE, Gonzales RG: Diffusionweighted MR Imaging of the brain. Radiology 217:331345, 2000 26. Petrella JR, Provenzale JM: MR perfusion imaging of the brain: Techniques and applications. AJR Am J Roentgenol 175:207-219, 2000 27. Meder JF, Blustajn J, Trystram D, et al: Radiologic anatomy of segmental agenesis of the internal carotid artery. Surg Radiol Anat 19:385-394, 1997 28. Graham CB, Wippold FJ, Capps GW: Magnetic resonance imaging in internal carotid artery agenesis with computed tomography and angiographic correlation— Case reports. Angiology 50:847-853, 1999 29. Cali RL, Berg R, Rama K: Bilateral internal carotid artery agenesis: A case study and review of the literature. Surgery 113:227-233, 1993 30. Czarnecki EJ, Silbergleit R, Mehta BA, et al: Absence of the supraclinoid internal carotid artery in association with intracranial aneurysms. Neuroradiology 40: 11-14, 1998 31. Harps E, Helmke K: Diagnosis of congenital absence of internal carotid artery by power angio sonography. Eur Radiol 8:1245-1247, 1998 32. Breidahl WH, Khanguhj MS: Case report: MRI diagnosis of congenital absence of the internal carotid artery. Clin Radiol 42:354-355, 1990 33. David H, Dubayle P, Girodeau A, et al: Agenesis of the internal carotid artery: Two cases report. J Radiol 81:147-150, 2000 34. Kane AG, William PD, Barkovich J, et al: Reduced caliber of the internal carotid artery: A normal finding with ipsilateral absence or hypoplasia of the A1 segment. AJNR Am J Neuroradiol 17:1295-1301, 1996 35. Jordan JA, Lewis M, Rollins N, et al: Congenital internal carotid artery aneurysm with absence of the petrous portion of the contralateral internal carotid artery. Ann Otol Rhinol Laryngol 109:1167-1169, 2000 36. Nezu N, Ninchoji T, Kitanaka H, et al: A case of congenital absence of the left internal carotid artery. Comput Radiol 8:355-360, 1984 37. Murotani K, Hiramoto M: Agenesis of the internal carotid artery with a large hemangioma of the tongue. Neuroradiology 27:357-359, 1985 38. Wang PJ, Liu HM, Young C, et al: Agenesis of internal carotid artery associated with symptomatic partial epilepsy. Epilepsia 35:1337-1341, 1994