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 Table of Contents  
Year : 2022  |  Volume : 34  |  Issue : 3  |  Page : 320-323

Cone-Beam computed tomography a dynamic tool for assessment of canalis basilaris medianus a skull anomaly – A retrospective study

1 Oral Medicine and Radiology, Dr. D.Y. Patil Dental College and Hospital, Pune, Maharashtra, India
2 I.I.T., Madras, Tamil Nadu, India

Date of Submission18-Nov-2021
Date of Decision18-Jul-2022
Date of Acceptance19-Jul-2022
Date of Web Publication26-Sep-2022

Correspondence Address:
Lavanya H Pasalkar
Dentalbliss, 4/273, Nigdi Pradhikaran, Pune, Maharashtra - 411 044
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiaomr.jiaomr_329_21

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Introduction: Canalis basilaris medianus (CBM) is an anomaly of basiocciput in the clivus at the skull's base, demonstrating six different morphological varieties. CBM can be associated with recurrent meningitis and various other cranial pathologies. It can be seen on maxillary cone-beam computed tomography (CBCT) scan with comparatively less radiation dose than computed tomography (CT). Aim: The aim of this study is to determine a prevalence of CBM on CBCT. Objectives: The objectives of this study are: 1. To identify CBM on CBCT 2. To classify CBM according to their morphological types using CBCT. Methods and Material: This study included 300 maxillary CBCT scans retrieved from archival records from the CBCT diagnostic center, Department of Oral Medicine and Radiology, and the existence of CBM were examined. Scans of both genders with all age groups were selected. The existence of CBM was examined and classified based on its morphological type. Results: Chi-square test was used to carry out the descriptive statistics. The presence of CBM was found in 16 scans with a prevalence rate of 5.33%. Out of 16 scans, 10 (62.5%) were females, and 6 (37.5%) were males. Among them, 13 (81.25%) scans were superior recess variety, and 3 (18.75%) were inferior recess variety; other morphological types were absent. Conclusion: Although the prevalence rate of this anomaly is low, it is clinically significant as it may cause the spread of nasopharyngeal infections to the skull base. The present study revealed that a CBCT scan of the maxillary arch could provide a clear delineation of CBM with comparatively less radiation dose than CT. To the best of our knowledge, the recorded values of the prevalence rate of CBM available in current literature are lower compared to this first-ever study carried out in India.

Keywords: Canalis basilaris medianus (CBM), computed tomography (CT), cone-beam computed tomography (CBCT)

How to cite this article:
Pasalkar LH, Chavan MS, Sonawane SR, Sarma A, Helge B, Tilekar S. Cone-Beam computed tomography a dynamic tool for assessment of canalis basilaris medianus a skull anomaly – A retrospective study. J Indian Acad Oral Med Radiol 2022;34:320-3

How to cite this URL:
Pasalkar LH, Chavan MS, Sonawane SR, Sarma A, Helge B, Tilekar S. Cone-Beam computed tomography a dynamic tool for assessment of canalis basilaris medianus a skull anomaly – A retrospective study. J Indian Acad Oral Med Radiol [serial online] 2022 [cited 2022 Dec 10];34:320-3. Available from: http://www.jiaomr.in/text.asp?2022/34/3/320/356961

   Introduction Top

The emergence of cone-beam computed tomography (CBCT) has extensively revolutionized maxillofacial imaging with its vast range of applications.[1] Computed tomography (CT) is the gold standard for craniofacial imaging as it provides accurate images, facilitating definite assessments, but it comes with a higher effective dose. Like CT, CBCT is a maxillofacial imaging modality that provides slices in sagittal, coronal, and axial, but with added advantages of a large field of view and visualization of the clivus and surrounding bony structures, high diagnostic yields, low risk, and low cost.[1],[2] Clivus is a sloping mid-point present at the skull base, formed after the fusion of the basisphenoidal and basioccipital bones.[2],[3] In 1880, Grubber first described Canalis Basilaris Medianus (CBM) as an uncommon variant/anomaly of basiocciput in clivus. It consists of a well-defined channel that originates on the intracranial surface of the basiocciput in the midline (canalis chordae).[4] There are three varieties of complete CBM: superior, inferior, and bifurcated, and three varieties of incomplete CBM: thin long channel, superior recess, or an inferior recess[3],[5] [Figure 1][3] Although the occurrence of CBM is low, studies have shown that it may lead to recurrent meningitis and spread of nasopharyngeal infections to the skull base.[2],[3],[5] Dento-maxillofacial radiologists should identify and interpret such anatomical variations to prevent further evaluation. The current literature lacks information, especially in the field of dentomaxillofacial radiology. No prior study has been reported in India giving a prevalence of CBM using CBCT. Therefore, this study was undertaken to find the prevalence of CBM and classify them according to their morphological types using CBCT.
Figure 1: Types of CBM complete variety: (1) bifurcating, (2) inferior, (3) superior. Incomplete variety: (4) inferior recess, (5) superior recess, (6) channel

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   Subjects and Methods Top

Ethical clearance was obtained from the institutional ethical committee held on 13/11/2019. (ref no: DYPDCH/IEC/124/138/19). Sample size estimation was done using N = 4PQ/D2 (N = Number, P = Prevalence = 2.5%, Q = 1-P, D = Error = 2, Power = 80%). As per the estimated sample size, 300 scans of the maxillary arch done in the year 2018–2019 were retrieved from archival records using convenience sampling from the CBCT diagnostic center of the Oral Medicine and Radiology Department after obtaining a waiver of consent from the ethical committee as the nature of the study was retrospective. For patients with a history of trauma/surgery involving the maxillofacial region or any other developmental and pathological anomalies, scans showing errors and artifacts obscuring visibility of structures in the maxilla or impacted teeth/implants in the anatomical area of interest were excluded.

A total of 300 CBCT scans (Male: 155, Female: 145) with all age groups were obtained by using the I-CAT 3D imaging system, parameters used for the scan are given in [Table 1]. The sagittal section of the CBCT scan was evaluated. CBM was characterized by a well-defined, corticated bony defect in bassiocciput, which was then classified according to their morphological type [Figure 1] and [Figure 2].
Figure 2: Types of recess (a, b, c) Superior recess; (d) Inferior recess

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Table 1: Parameters of CBCT scan

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Two maxillofacial radiologists evaluated all scans. The scans were examined and interpreted by radiologists twice. Scan with the presence of CBM was categorized by the observers separately. After repeated examination and differences in assessment, a final diagnosis was drawn.

   Results Top

Among 300 (males: 155 and females: 145) scans evaluated, CBM was found on 16 scans. The prevalence rate of CBM was 5.33%, out of which 6 (37.5%) were males, and 10 (62.5%) were females [Graph 1]. The inter-relationship between gender and CBM occurrence was not significant (P = 0.82). The mean age of subjects included in the study was 40.6 years in males and 41.5 years in females, respectively. The mean age of the subjects with the defect was 59.5 years in males and 50.8 years in females, respectively [Table 2]. The age-wise distribution of CBM is shown in [Graph 2].

Table 2: Mean age of the subjects with defect

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Out of the total 16 scans with CBM, 3 (18.75%) scans had inferior recess variety, and the rest of 13 (81.25%) were only recess type. Other morphological variants were not seen [Graph 3]. The superior recess variety has a significantly high prevalence rate (P = 0.5) than any other type of CBM.

   Discussion Top

In 1967 Sir Godfrey N. Hounsfield invented CBCT. Earlier in 1982, it was used in angiography, later used for imaging the maxillofacial region. CBCT is a widely emerging tool with high potential for imaging structures in the head and neck with high contrast.[6] Research showed that high resolution could be obtained for images with relatively low radiation doses to the patient.[7] CBCT images of the jaw demonstrate regions of the skull base which are out of the area of interest. In some instances, CBM, an anatomical variant, is seen at the base of the skull, which should not be confused with pathological formations.[3] Studies have shown that it may lead to recurrent meningitis and the spread of nasopharyngeal infections to the skull base.[2],[3],[5]

Martinez et al. and Hemphill et al. reported a case of a 19 month old boy with a history of recurrent meningitis. A complete canal in the basiocciput (similar to a CBM inferior) was found on radiological examination. There were no further bouts of the same disease seen in the child after surgical treatment of the bony defect with removal and grafting during a 36 month follow up.[3],[5],[8] Guido Currarino discovered two cases of children, one with neurofibromatosis and the other with Apert's syndrome, in whom a recess was found on the basiocciput in the inferior surface on CT scan as an incidental finding of the skull. The recess was interpreted as CBM-incomplete form. It is one of the six types of CBM. It is considered to be less clinically significant compared to a complete canal which can be differentiated from each other by a CT scan with reformatted images.[3] Sagittal sections of CBCT can be used when the skull base is covered in the field. Lohman et al.[9] also gave a case of Tornwaldt cyst showing association with CBM. Morabito et al.[10] presented CBM-related pharyngeal enterogenous cysts in a newborn. Bayrak et al.[2] studied the prevalence of CBM in 1059 patients aged 15–75 years and found a 2.5% CBM prevalence. The estimated occurrence of CBM in a series of skulls has seen approximately 2–3% and 4–5% in adults and children, respectively.[5] Most of the studies for CBM and other skull base anomalies in the literature have been done on dry skulls, but some have been seen on conventional radiography and CT scans of the skull, and still, fewer have been done using CBCT scans.[2]

In this study, we have evaluated the prevalence of CBM using CBCT scans of the maxillary arch; the total number of scans involved were 300 for all age group. CBM prevalence obtained is 5.33%, almost double that of the currently available literature value. In our study, the prevalence rate was found to be more in females than males, but due to the small study population, more research with a bigger size has to be done. Only superior recess and inferior recess were noticed, with superior recess being the most common. Because there is a lack of literature regarding a study of prevalence depending on morphological types of CBM, a comparison cannot be made. Moreover, the pathology caused by CBMs in our study population could not be evaluated as the nature of our study was retrospective.

   Conclusion Top

Even though the global prevalence rate of this anomaly is very low, our study can conclude that this first-ever study carried out in India showed that the CBM prevalence rate is higher compared to the existing literature. CBM is clinically significant as it may cause skull base infection by spreading nasopharyngeal infections. Though a CT scan is the gold standard to detect such anatomical variation in the skull base, a CBCT scan obtained for dentofacial structure with much less radiation dose can show this anomaly as an incidental finding during radiographic examination. So radiologists should be aware of such anomalies and their radiographic appearance to avoid further investigation.


The existence of CBMs and correlation of clinical features, if present, could not be evaluated as the nature of our study was retrospective.

Future prospects

Maxillary CBCT scans can be traced for this incidental finding. The patient showing CBM can be clinically correlated and made aware of the existence of a variant in case an idiopathic complication arises later in life. Also, patients with a history of recurrent skull base infections can be advised CBCT scan to evaluate the presence of CBM.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Key messages

CBM is an anatomical variant seen at the base of the skull. It may lead to recurrent meningitis and the spread of nasopharyngeal infections to the skull base. CT scan is the gold standard to detect anatomical variation in the skull base, but a CBCT scan with much less radiation can show this skull anomaly.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Ghali SR, Katti G, Shahbaz S, Katti C. Cone beam computed tomography: A boon for maxillofacial imaging. J Indian Acad Oral Med Radiol 2017;29:30-4.  Back to cited text no. 1
  [Full text]  
Bayrak S, Göller Bulut D, Orhan K. Prevalence of anatomical variants in the clivus: Fossa navicularis Magna, canalis basilaris medianus, and craniopharyngeal canal. Surg Radiol Anat 2019;41:477-83.  Back to cited text no. 2
Currarino G. Canalis basilaris medianus and related defects of the basiocciput. AJNR Am J Neuroradiol 1988;9:208-11.  Back to cited text no. 3
Jacquemin C, Bosley TM, Al Saleh M, Mullaney P. Canalis basilaris medianus: MRI. Neuroradiology 2000;42:121-3.  Back to cited text no. 4
Syed AZ, Zahedpasha S, Rathore SA, Mupparapu M. Evaluation of canalis basilaris medianus using cone-beam computed tomography. Imaging Sci Dent 2016;46:141-4.  Back to cited text no. 5
Hemphill M, Freeman JM, Martinez CR, Nager GT, Long DM, Crumrine P, et al. A new, treatable source of recurrent meningitis: Basioccipital meningocele. Pediatrics 1982;70:941-3.  Back to cited text no. 6
Miracle AC, Mukherji SK. Conebeam CT of the head and neck, part 2: Clinical applications. AJNR Am J Neuroradiol 2009;30:1285-92.  Back to cited text no. 7
Martinez CR, Hemphill JM, Hodges FJ 3rd, Gayler BW, Nager GT, Long DM, et al. Basioccipital meningocele. AJNR Am J Neuroradiol 1981;2:100-2.  Back to cited text no. 8
Lohman BD, Sarikaya B, McKinney AM, Hadi M. Not the typical Tornwaldt's cyst this time? A nasopharyngeal cyst associated with canalis basilaris medianus. Br J Radiol 2011;84:e169-71.  Back to cited text no. 9
Morabito R, Longo M, Rossi A, Nozza P, Granata F. Pharyngeal enterogenous cyst associated with canalis basilaris medianus in a newborn. Pediatr Radiol 2013;43:512-5.  Back to cited text no. 10


  [Figure 1], [Figure 2]

  [Table 1], [Table 2]


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