Approaches to the craniocervical junction are undertaken for a variety of reasons. Congenital conditions such as platybasia may alter the anatomy, and should be taken into consideration when considering the approach. Recently several endoscopic approaches have been proposed including a pure transnasal approach and an endoscopic transcervical approach. In a prior study, we suggested lesions with significant inferior extention could be accessed through the a combined endo nasal/endo oral approach.(20
) () Other authors have suggested that a transcervical approach is advantageous to avoid pharyngeal contamination.(16
) This study highlights the variability in patients’ anatomy and demonstrates that a “one approach for all” is not appropriate. Our case series illustrates that patients with platybasia who have craniocervical junction pathology would be difficult to access either through a transcervical approach or through a transoral corridor.
Intraoperative photographs of Combined Endo nasal/Endo oral Approach
Basilar invagination may be congenital or developmental.(21
) Congenital malformations involving the occipital bone, atlas, and axis can be associated with basilar invagination (i.e. condylar hypoplasia, assimilation of atlas, and axial segmentation failure). On the other hand, Paget’s disease, rheumatoid arthritis, or excessive weight loading during childhood may cause a developmental upward protrusion of odontoid process and resultant ventral compression of brain stem. Not uncommonly, a mixture of the two processes is encountered in clinical practice. Furthermore, the two reciprocally overlapping entities might be treated from different surgical strategies. Despite the presence of ventral brain stem compression, decompression from an anterior approach is not always necessary. Reduction of deformity from a posterior approach in combination with occipito-cervical fixation (without anterior decompression) has been reported to be successful.(22
Our data indicates that the condition of platybasia is commonly associated with a rise of the odontoid tip over the plane of the hard palate. In a prior report in the literature examining the relationship of the odontoid tip to the nasal floor, the authors reported the height of the odontoid to range from −9mm to +18.7mm over the palate.(26
) We have found that the palatine line appropriately guides this new surgical perspective endonasally. The height of craniocervical junction in reference to this line is an important predictor of accessibility through an endonasal approach. The choice of endonasal versus endoral approach has to do with a combination of the position of the palate and the height of the odontoid. When the surgical target lies at 2 cm above the palate, it appears the endonasal approach is the better approach.
De Almeida et al(26
) examined the limit of endoscopic approaches to the craniocervical junction by defining a line drawn from the nasal bones to the posterior hard palate as the nasalpalatine line. They reported that this line intersects the spinal column at a mean of 8.9 mm (range −9.0–8.7 mm) above the base of the C2 body. However, the purely transnasal approach as described, requires resection of a significant portion of the nasal cavity and sinuses including the middle turbinate, the unilateral ethmoids and posterior nasal septum. The resultant large cavity causes significant nasal morbidity in the form of mucus crusting and possibly atrophic rhinitis and requires the patient to perform lifelong daily nasal irrigations. Although De Almedia has demonstrated that most lesions of the craniocervical junction can be reached from the nasal corridor, it is questionable whether all lesions should
be approach from this corridor due to the consideration of patient morbidity. By using a second corridor through the oral cavity, little morbidity is added, and it may be possible to avoid extensive dissection in the oral cavity. Thus, instead of asking if the surgery can be done through the nasal cavity, the surgeon should question if the surgery needs to be done purely through the nose. In our series, we found only two patients with extreme superior position of the odontoid requiring a purely nasal approach. Other patients could be managed with a combined approach or endo oral approach, thereby avoiding extensive nasal dissection.
This case series reveals that the relation of the craniocervical junction to the nasal cavity is significantly altered when platybasia is present. Examinging our data, the palatine line appears useful, in addition to the nasopalatine line, to guide the choice of approach in patients with platybasia. Since platybasia is associated with a high lying odontoid process, a transoral approach may not allow adequate access without a palate split, and increased morbidity. Therefore, in conditions requiring treatment for basilar invagination with platybasia, we believe adding the concept of palatine line allows improved endoscopic approach selection.
This study may suffer bias from patient selection due to the fact our series only includes patients presenting for surgery. Since symptoms of basilar invagination are due to elevation of the height of the odontoid, the height of the odontoid and C1 ring would be expected to be increased. However we also looked at the height of the clival tip, which should predict the relative location of the odontoid before it started to slip. Further studies of larger populations of patients are necessary to determine if this finding holds true only in the diseased state, or if it is a true anatomic relation. Such a study is being initiated at our institution.
Predicting the best corridor for approach to the craniocervical junction can help reduce patient morbidity and improve surgical efficiency. Attempting to do all procedures using a single approach is not ideal, and anatomic variability has to be identified and acknowledged. The palatine line can be used to identify the appropriate corridor of approach. In our practice we have found that lesions can be located above, at, or below the palatine line with significant variability. This line along the palate floor appears to be an important line because it represents the access that can be achieved through an endoscopic transnasal approach as instruments are brought in through the nose and limited inferiorly by the hard palate. Although an expanded endonasal approach can provide additional lower resection with the use of an angled endoscope, the technical challenge of the approach increases in such cases.(26
De Almeida et al(26
) described measurements indicating that lesions of the odontoid may be accessed from below the palate by angling up into the soft tissue of the nose. Baird et al also compared the extent of resection between endonasal, transoral, and transcervical approaches. (27
) However, the palatine line that we have described in association with the position of odontoid process should be deemed as a categorization tool. It might assist endoscopic surgeons to identify an easy working channel preoperatively. In this study, analysis of cases using the palatine line (extension along the hard palate) reveals the elevated position of odontoid in patients with platybasia is evident from a surgical perspective Preoperative assessment in relation to the palatine line allows categorization of surgical targets in patients with and without platybasia. In our series we have found that we can reach lesions extending below this line much more easily by opening the oral cavity and working through two corridors (combined endo-nasal and endo-oral approaches). () We prefer a combined approach in such cases because a pure transnasal corridor may require destruction of the nasal anatomy (i.e. resection of the middle turbinate, sphenoid walls and posterior septum) to have adequate working room. If the oral corridor is used, then an endoscope can be brought in through the nose, while instruments come in through the oral cavity with preservation of the nasal anatomy thus avoiding the need for an expanded endonasal approach. ()