|Year : 2020 | Volume
| Issue : 3 | Page : 111-114
Morphometry of nasopalatine line for transnasal endoscopic access to craniovertebral junction: A cadaveric study
D Bharathi1, Deepali Deshatty2, BN Shruthi2
1 Assistant Professor, Department of Anatomy, Rajarajeswari Medical College and Hospital, Bengaluru, Karnataka, India
2 Associate Professor, Department of Anatomy, Rajarajeswari Medical College and Hospital, Bengaluru, Karnataka, India
|Date of Submission||02-Jul-2020|
|Date of Decision||30-Jul-2020|
|Date of Acceptance||23-Sep-2020|
|Date of Web Publication||15-Oct-2020|
Department of Anatomy, Rajarajeswari Medical College and Hospital, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
Background and Aims: Lesions in craniovertebral junction (CVJ) are approached either through transnasal or transoral route. Endoscopic transnasal route reduces significant morbidity, and nasopalatine line (NPL) predicts the inferior-most limit of surgical dissection. The purpose of the present study was to measure the NPL in the cadavers, which is beneficial for the endoscopic transnasal anterior approach to access odontoid process and anterior CVJ, especially in surgical decompression of medulla oblongata. Materials and Methods: The present study was done on forty midline sagittal head-and-neck specimens obtained from 10% formalin-fixed cadavers in the Department of Anatomy, Rajarajeswari Medical College and Hospital, Bangalore. Using slide calipers, the hard palate line (HPL), which extends from the anterior nasal spine of maxillary bone to the posterior nasal spine of palatine bone and NPL which extends from the inferior-most point of nasal bone to the posterior nasal spine were measured. In addition, HPL was extended to the lower limit of the anterior margin of the foramen magnum, and NPL was further extended posteriorly to the ventral surface of the second cervical vertebra to know the inferior limit of transnasal endoscopic access for surgeries on ventral skull base lesions. Results: The average of HPL and its extension to foramen magnum was found to be 45.83 mm and 40.97 mm respectively. The NPL and its extension to the ventral surface of C2 vertebra were found to be 58.22 mm and 37.18 mm, respectively. Conclusion: HPL & NPL provide useful information for the neurosurgeons to access the lesions in the ventral CVJ and to achieve a good outcome.
Keywords: Craniovertebral junction, endoscopic endonasal approach, morphometry, nasopalatine line
|How to cite this article:|
Bharathi D, Deshatty D, Shruthi B N. Morphometry of nasopalatine line for transnasal endoscopic access to craniovertebral junction: A cadaveric study. Natl J Clin Anat 2020;9:111-4
|How to cite this URL:|
Bharathi D, Deshatty D, Shruthi B N. Morphometry of nasopalatine line for transnasal endoscopic access to craniovertebral junction: A cadaveric study. Natl J Clin Anat [serial online] 2020 [cited 2021 May 8];9:111-4. Available from: http://www.njca.info/text.asp?2020/9/3/111/298161
| Introduction|| |
The anatomical area formed by atlanto-occipital joint, atlantoaxial joint, clivus, and foramen magnum and odontoid process forms the craniovertebral junction (CVJ), which contains key neurovascular structures which includes the lower medulla and spinal cord, vertebrobasilar arterial system, and lower cranial and upper cervical nerves. These soft-tissue structures are protected by occipital condyles and C1–2 vertebra which forms the atlanto-occipital and atlantoaxial joints. Therefore, any lesion in this region may lead to neurovascular compression.
Minimally invasive surgeries for ventral skull base lesions are important to reduce the morbidity when compared to conventional transoral-transpharyngeal approach. This approach requires glossotomy, mandibulotomy, maxillotomy, and palatotomy, which results in a significant increase in morbidity and hence prolongs hospital stay.
The extradural lesions of the odontoid process were resected by transoral approach, which is considered gold standard. However, the first case of complete endoscopic transnasal approach was done in 2005, to resect the odontoid process in a patient with cervicomedullary junction compression. The transnasal endoscopic approach to the ventral skull base reduces the surgical morbidities with less postoperative complications and provides closer and brighter views of surgical areas., The main limitation for the transnasal endoscopic approach to access the lesions in CVJ is the inferior exposure due to the presence of bony structure and soft tissues of nose and palate. Hence, knowledge of the nasopalatine line (NPL) helps to understand the inferior limit of the transnasal endoscopic approach to the CVJ.
The purpose of the study was to measure the NPL for transnasal endoscopic approach for surgical access to the odontoid process and anterior CVJ.
| Materials and Methods|| |
The present study was done on forty midline sagittal head-and-neck specimens obtained from 10% formalin-fixed cadavers in the Department of Anatomy, Rajarajeswari Medical College and Hospital, Bangalore.
Adult cadavers, both male and female, between the age group 20 and 60 years, were included in the study, and the specimens with cervical deformities were excluded from this study.
The parameters which were measured are hard palate line (HPL) and NPL using slide calipers on the midline sagittal section of head-and-neck specimens as shown in [Figure 1]. These measurements can be used to know the inferior extent of transnasal endoscopic approach in CVJ lesions.
|Figure 1: Midline Sagittal section of Head and Neck showing bony landmarks for measuring Nasopalatine line A: Posterior nasal spine of palatine bone, B: rhinion, C: anterior nasal spine of maxillary bone, D: ventral surface of C2 vertebra, E: anterior margin of foramen magnum, HPL: line joining points A to C (black). NPL: line joining points A to B (purple). Extension line 1: from point A to D (red) and extension line 2: From point A to E (black)|
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Hard palate line
HPL extends from [Figure 1] the anterior nasal spine of the maxillary bone to the posterior nasal spine of the palatine bone (line joining points A to C). It is further extended posteriorly to the lower limit of the anterior margin of the foramen magnum (Extension line 2: From point A to E).
NPL extends from [Figure 1] the inferior-most point of nasal bone (rhinion) to the posterior nasal spine of the palatine bone (line joining points A to B). This line is extended posteriorly to end at the midpoint on the ventral surface of the second cervical vertebra at the level of the lower border of the atlas (Extension line 1: from point A to D).
Mean and standard deviation (SD) were calculated.
| Results|| |
The hard palate length is the primary measurement used to calculate the inferior limit of the transnasal endoscopic approach, and it is used as fulcrum for maneuvering the endoscope. In our study, the mean and SD of HPL were 45.83 mm and 4.14 mm. Its extension to inferior margin of foramen magnum was 40.97 mm with SD of 4.27 mm as shown in [Table 1] and [Table 2], respectively.
|Table 2: Measurements of distance between posterior nasal spine to the anterior margin of foramen magnum (mm) (extension line 2)|
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In the present study, we are using the principle of NPL as described by de Almeida et al. to determine the lower limit of the endonasal approach. The mean of NPL was 58.22 mm with SD of 4.64 mm. Its extension to the ventral surface of C2 vertebra was 37.18 mm with SD of 4.85 mm as shown in [Table 3] and [Table 4], respectively.
|Table 4: Measurements of distance between posterior nasal spine to midpoint of ventral surface of second cervical vertebra (mm) (Extension Line 1)|
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| Discussion|| |
de Almeida et al. reviewed retrospectively computed tomographic scans of 17 patients who underwent transnasal endoscopic approach. HPL and NPL in the midsagittal plane were defined.
Minimally invasive endoscopic surgeries, such as endoscopic endonasal approach (EEA) for ventral skull base lesions, have shown a significant rise in the past decade.,,, Thus, it becomes imperative for the team of neurosurgeons and otorhinologists to understand the relationship between the hard palate, foramen magnum, dens of axis, and atlas to maneuver efficiently using the endonasal endoscopy to optimally access the ventral skull base lesions. Fiber-optic endoscopes allow neurosurgeons to view and operate, providing improved dexterity and safety in skull base surgeries.
The surgical indication for CVJ-odontoid access is an extradural compression lesion, the basilar invagination, usually secondary to rheumatoid arthritis, exostosis, osteotoma, or other disorders such as foramen magnum meningiomas and clivus chordomas. Evaluation of the extension of the lesion is imperative to determine which ones can be approached endonasally. In terms of feasibility of the approach, the NPL, which is also known as Kassam's line is the keystone in surgical planning.
The use of a transnasal approach to access the anterior structures of the upper neck was first reported in an anatomical study by Alfieri et al. in 2002. Lega et al. compared endoscopic transoral and transnasal approach by reviewing computed tomography (CT) scans of 41 patients undergoing imaging for intracranial carotid stenosis, subarachnoid hemorrhage, and neurovascular diagnoses. The midsagittal measurements of HPL on average were found to be 48.30 mm and NPL was 67.63 mm and concluded that, through the endoscopic transnasal approach, lesions which are 22 mm below the hard palate plane can be reached.
Aldana and Roy  described the nasoaxial line (NAxL) in predissected scans of nine cadaveric heads since NPL overestimated the lower limit of the upper cervical spine. NAxL is the line joining the midpoint of rhinion and anterior nasal spine to the posterior nasal spine of the palatine bone. It is then extended posteriorly to end at the C2 vertebra.
According to La Corte et al., NAxL overestimated the lower limit of transnasal endoscopic approach to CVJ; therefore, they reviewed retrospectively six patients who underwent surgery. He described a novel rhinopalatine line (RPL), which was constructed on sagittal magnetic resonance imaging and CT scans. This line extends from two-third of the distance between rhinion and the anterior nasal spine to the posterior nasal spine. Further, this line is extended to the cervical spine. Radiographic measurements of NPL, NAxL, and RPL were found to be 32.1 mm, 17 mm, and 11.9 mm, respectively. They concluded that RPL is more accurate in predicting the lower limit of the transnasal endoscopic approach to the anterior CVJ.
Morphometric analysis of the hard palate length, distance, and angle between hard palate and the odontoid process was done by Singh et al. using computerized tomographic scans of 100 patients. In addition, simulation of endoscopic visualization was done, and lines were projected from the hard palate to the cervical spine at 0°, 30°, and 45°. An inverse relationship was found between hard palate length and lower limit of cervical spine. In part 2 of the study, the Singh et al. did endoscopic endonasal study on ten cadavers for endonasal visualization of the cervical spine. The study design of various authors is depicted in [Graph 1].
In our study, we have used the anatomical bony landmarks in cadavers to measure the NPL, which can be utilized by neurosurgeons as baseline data for preoperative planning to access the CVJ through transnasal endoscopic approach.
| Conclusion|| |
In our literature review, we have found that large-scale cadaveric study on NPL has not been done so far. Our findings of the cadaveric study of NPL and its extension to the midpoint of the second cervical vertebra at the level of the lower border of atlas provide valuable data for neurosurgeons for maneuvering the endoscope in the transnasal corridor for access to the CVJ.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]