Morphometric Analysis of parameters of Internal Carotid Artery—Potential Clinical Implications
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.333479
Source of Support: None, Conflict of Interest: None
Keywords: DSA, internal carotid artery, morphometric measurements
Theory of blood circulation was given by William Harvey in 1600. For the first time in the world, Egyptians wrote about brain in Edwin Smith papyrus and in 1664 study was carried out on neuroanatomy and angiology which was done by Thomas Willis.
First description of the arteries present at the base of the brain (circulus arteriosus cerebri) originates as far back as 1658. Thomas Willis gave a detailed description of these arteries in 1664. So, it was named as Circle of Willis.
Angiography of brain
One of the crucial imaging techniques used for diagnosis as well as evaluation before surgical interventions of the various pathologies of brain was angiography. Angiography being an invasive procedure was responsible for some complications, therefore led to the intra-arterial technique of digital subtraction angiography (DSA). DSA uses smaller doses of contrast, smaller caliber of catheters, and procedure duration were shortened. Being a real time study, it helps in assessment of carotid and vertebro-basilar systems. It also gives information about vascular transit time. Hence DSA helps in the diagnosis of various intracranial anomalies like aneurysms and A-V malformations (AVM). This also furnishes details of measurements of cerebral vessels. Hence DSA helps in getting idea of occlusion of cerebral vessels and is therefore crucial in planning various surgical and interventional neurological procedures.
One of the advantages of rotational angiography is that C-arm has high speed of rotation, high speed accession of images, dimensional resolution, and accuracy of 3D images. Therefore, rotational angiography has high resolution. 3D quality and resolution of images of DSA is perfect.
Internal carotid artery (ACA)
The internal carotid artery (ICA) is formed from seven segments. The first C1 (cervical) segment develops from third aortic fetal arches. Rest of the segments C2–C7 (petrous to communicating) develop from cranial extensions of embryonic dorsal aorta. Internal carotid system consists of ICA and its major branches. Anatomically, ICA is made of intracranial and extracranial. Moreover, intracranial section is made of three parts: petrous, cavernous, and cerebral. ICA enters the cranium through the carotid canal from base of the skull which is located at petrous temporal bone's base. The first division named as cervical is from the point of division of CCA till the entry of ICA into base of skull via carotid foramen. The second segment (ascending petrous) continues within petrous bone from the apex of antero-medial curvature till carotico-tympanic artery is given. Horizontal petrous is the third segment in the foramen lacerum at the skull base. From the cavernous sinus till the origin of meningo-hypophyseal trunk is the fourth segment (ascending cavernous). ICA takes anterior–inferior course at the origin of meningo-hypophyseal trunk. The horizontal cavernous (fifth) segment is present in the cavernous sinus starting from meningo-hypophyseal trunk and ending at infero-lateral trunk. The clinoidal (sixth) segment continues from infero-lateral trunk till adult OA. The seventh segment which the last part lies between the ACA and primitive OA [Figure 1].
The P-ICA which is the petrous part of ICA is a dubious part, not easily approachable for imaging. The parasellar ICA or the cavernous part of ICA (C-ICA) looks like a siphon. It is tortuous and twisted. It is encircled by venous web. Because of its characteristic shape, it is a topic of immense interest and correlated with regulation of temperature in brain and also with various arterial pathologies. This part of ICA is most prone to atherosclerosis. Knowledge of hemodynamic distribution in the cerebral arteries is useful for comprehension of cerebrovascular diseases like intracranial aneurysms and their pathophysiology.
Knowing cerebrovascular dimensions is the key for performance of stents and flow diverters and other endoluminal prostheses. Manufacturing of endovascular instruments depends on cerebrovascular dimensions used for treatment of endovascular aneurysms. It was noted that insufficient knowledge of anatomical variations cause dozens of medical errors, and that's why it is mandatory to assess the circulatory system condition of the brain as part of preoperative neurosurgical preparation of patients. The basic knowledge of intracranial blood vessels is essential for surgeons and their surgical treatment planning and radiologists.
Aim and objectives
The present study aims to determine the morphometry of ICA through DSA evaluation and to build a normative data which is accurate enough for the neurovascular procedures to be performed. The study will also carry out correlation of morphometry of intracerebral blood vessels with sex, age, and side-related dimorphism.
The study was cross-sectional in design including 70 patients for the morphometric measurements of ICA by DSA both in the Departments of Anatomy and Radiology at AIIMS, Jodhpur.
Institutional Ethics Committee clearance before commencement of the study. Informed consent was taken from the patients involved in the study. Ethics committee Date of approval by 29.09.2017.
Patients who had come for DSA evaluation and aged more than 20 years were enrolled in the study.
Arteries with pathological segments (dysplasia, aneurysms, dissections) were excluded from the study.
Philips biplane system clarity (Allura FD20/20) of DSA was used for the study with Seldingher technique being to obtain access of femoral artery. The adequacy of femoral arterial pulsations on palpation determined the use of 18 G or a 21 G needle for arterial access under ultrasound guidance, as and when required. Selective angiograms of ICA were obtained by using H1 or Simmons 15Fr diagnostic catheter. Acquisition of images were done in antero-posterior (37 cm or 42 cm) and lateral planes (42 cm) at 2 frame per second. Auto-calibration on DSA console was used for measurements.
Diameters of the following vessels were taken
Data was analyzed using SPSS software (21 version). Calculation of Mean and standard deviation was done. ANOVA test and Student's t-test were used for calculating comparison of groups.
Mean diameters of various segments of ICA of both right and left sides were calculated for all 70 patients. Data was classified according to gender and age (42%male) with patients in age group 20–39 years, 40–59 years, above 59 years being 35.7%, 48.6%, and 15.7%, respectively [Chart 1] and [Chart 2].
Mean diameter of petrous, cavernous, supraclinoid, and choroidal segments of ICA [Table 1] were more in males as compared to females. This difference was found to be statistically significant in supraclinoid segment of ICA (P value 0.022). Intergroup analysis between male and female was done using unpaired Student's t-test and between different age groups ANOVA test was used.
The mean diameter of supraclinoid and choroidal segments of ICA followed decreasing trend from younger to older age group [Table 2]. There were statistically significant differences in the mean diameter of petrous segment of ICA among different age groups (P value- 0.012). [Chart 3],[Chart 4],[Chart 5],[Chart 6] shows the scatter plot of diameter of various segments of ICA namely petrous, cavernous, supraclinoid, and choroidal, respectively, versus age; with diameter taken on Y-axis and age on X- axis and showed positive correlation for petrous segment whereas negative correlation for cavernous, supraclinoid, and choroidal segments of ICA.
Primarily various vascular channels form in brain. These vascular channels are the precursors of cerebral blood vessels. Certain vascular channels disappeared and some persisted. Mechanism of angiogenesis is sprouting, hypoxia or ischemia being the driving factors. Larger arteries have reduced impedance to flow. Remodeling of arteries supplying various areas is facilitated by flow and formation of new arteries. The development of circulatory system at the 1.3 mm embryonic stage is marked by formation of six pairs of primitive branchial arch arteries which undergo heavy modifications during further course of development.
Most of the branches of CW formed from ICA develop from the third pharyngeal arch artery. Internal carotid develops as rostral and caudal segments. Rostral part is further divided into medial and lateral branches. The medial branch is the primitive form of anterior cerebral artery complex in human beings, whereas in fishes it is separate. The caudal part constitutes the basilar trunk and supplies the posterior cranial fossa, posterior cerebral artery is the prolongation of caudal part of internal carotid artery. BA is derived by the cranio-caudal fusion of posterior division of ICA. PCOMM, a segment of PCA and upper basilar system have their origin from the caudal division of ICA.
Various pathologies like cerebral aneurysms, strokes, and ischemia can be assessed and managed by devices for endovascular interventions which needs through knowledge of morphometry of cerebral arteries. Various studies done previously have described the morphometry of ICA, ACA, MCA, ACOMM, and PCOMM in cadaver and by MRAs. Cadaveric studies have the limitation that measurement of external diameter of the vessels cannot be measured. The present study describes arterial dimensions by DSA. The study of length and diameter of vessels becomes significant as the arteries are small and tortuous and pathological occlusion of the vessels has non-linear flow characteristics.
Various studies related to morphometry of ICA are compared in [Table 3]. In the present study, the mean diameter of petrous, cavernous, supraclinoid, and choroidal segment of ICA were similar to the study of Arat YO et al. in 2015 and dissimilar to the MRA findings of Krabbe-Hartkamp et al. and Rai et al.'s study based on CTA (5 mm)., Vijaywargiya M et al. observed that right side petrous segment of ICA measured 3.88–.06 mm, while that of left side was 4.01–4.18 mm; and that for the cavernous segment was 3.81–3.89 mm, and 3.85–4.07 mm on the right and left sides, respectively. While Kane et al. noted the ICA diameter to be 4.65 mm on the right and 4.59 mm on the left side. Tarasow E et al. in their DSA study had the range of diameter between 2.43 and 4.18 mm and that in MRA study had the range of 2.72 and 3.46 mm. They also observed that the diameter was more in male; and it had an increasing trend with age. The finding was 3.79 mm by Shatri J et al.; similar results were shown by Karatas et al. (3.55 mm) in Turkish population and Maaly et al. (3.72 mm) in the population of Egypt and Wollschlaeger et al.(3.7 mm),,,, while the result of Kamath et al. was 4.2 mm in the population of U.S.A.,
Our study showed mean diameter of all segments of ICA were more in male as compared to female.
This difference in male and female was found to be statistically significant in supraclinoid segment of ICA. Toyota et al. also observed higher values of ICA diameters in the males. Krabbe-Hartkamp et al. also stated that the ICA was wider in men than in women, which was also similar to findings of Macchi et al. in TCD examinations. Toyota et al. and Gladilin et al. emphasized that the diameters of the ICA increase from adolescence to seniority., Our study showed a decreasing trend with increasing age in the mean diameter of supraclinoid and choroidal segment of ICA (mean diameter of supraclinoid segment of ICA for the age group 20–39 years was 3.70 mm, for 40–59 years was 3.60 mm, and for >59 years was 3.48 mm. Mean diameter of choroidal segment ICA for the age group 20–39 years was 3.38 mm, for 40–59 years was 3.33 mm, and for >59 years was 3.25 mm. Shatri et al. observed that the diameter was significantly greater in the younger population; and was nearly the same in both male and female population.
Various pathologic conditions which affect the diameter of ICA may result in focal narrowing, including adjacent neoplasm, atherosclerosis, arteritis, fibromuscular dysplasia, neurofibromatosis, and spasm. So, the present study can be provide useful information for resolving discrepancies in clinical suspicion of a serious disease. The larger width of supraclinoid segment of ICA may be an alarming sign; as diameter of this segment of ICA was observed to be larger in ACOMM aneurysm. The diameter of all the segments of ICA taken in the present study can allow the neurosurgeons to use new approaches during transsphenoidal surgical procedures. With the help of these measurements, ICA can be better protected during surgical manipulations [Figure 3].
Variations in the results may depend on a number of factors like selection of different subset of populations and use of varied techniques by different authors.
Knowledge of microvascular anatomy is very important and useful to understand peculiarity of vessels. Hence, it can decrease morbidity. Thus, knowing the dimensions of ICA has its importance in neurological examinations related to cerebral ischemia, and in neurosurgical operations, especially the clipping of an aneurysm located in this region as it is the most common site of intracranial aneurysm.
According to our study, the difference was statistically significant with respect to length of ICA and age. Knowledge of the arteries of the brain is important for the neurosurgeons in order to tackle the various pathologies in this region safely and confidently. Changes in the morphometry of the intracerebral arteries can also cause vascular insufficiencies for which prior standardization of morphometric data should be available for clinicians.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]