[The ventral approach to the dens epistropheus]

Basilar invagination associated with chiari malformation type I: A literature review

Basilar invagination (BI) and Chiari malformation type I (CM-I) are very important anomalies that introduce instability and compression in the occipitocervical transition region and have complex clinical characteristics. These anomalies vary according to the affected structures. The present study revises current knowledge regarding the anatomy, anatomo-physiology, clinical manifestations, and radiological findings of these entities and the associated surgical treatment approaches. A bibliographic survey was performed through a search in the Medline, PubMed, SciELO, Science and LILACS databases. When associated, these craniovertebral malformations result in neurological deficits due to neural parenchyma compression; however, the presence of microtraumas due to repetitive lesions caused by the bulb and cervical marrow instability has been highlighted as a determinant dysfunction. Surgical treatment is controversial and has many technical variations. Surgery is also challenging due to the complex anatomical characteristics and biomechanics of this region. Nevertheless, advances have been achieved in our understanding of related mechanisms, and compression and atlantoaxial instability are considered key elements when selecting the surgical approach.

A new, rolled-sponge technique for transoral exposure of C1 and C2

Instead of the general use of a catheter attached to the uvula or of catheters passed through the nasal cavity to the mouth for elevation of soft palate, the authors describe a new technique utilizing two rolled sponges producing maximum elevation of soft palate and good perioral cosmetic results for transoral exposure of C1 and C2.

Transoral operations for craniospinal malformations

The transoral approach to the lower third of the clivus and to the ventral aspect of the upper cervical spine is used in craniospinal malformations with or without dislocation as well as in basilar aneurysms, ventrally situated cranio-spinal tumours, fractures of the odontoid process, and in rheumatoid arthritis compressing the spinal cord. In consideration of the literature and ten personal cases the indications and techniques of the transoral approach in craniospinal malformations are discussed. According to our own experiences and those of other authors it is possible to expose the lower clivus and the cervical spine down to C2 by a midline incision of the pharyngeal wall using a mouth retractor and oral intubation. Splitting of the soft palate or resection of the hard palate are not necessary, a tracheotomy should be performed only in exceptional cases. In congenital craniospinal malformations without dislocation or instability causing a ventral compression of the spinal cord, for instance by the odontoid process, the transoral decompression is preferable to dorsal decompressing operations. In cases of pure instability without any space-occupying lesion the transoral and posterior approach are possible in order to perform a fusion. The last one seems more advantageous in these cases. In craniospinal malformations with dislocation causing a ventral and dorsal narrowing of the spinal canal, apart from the decompression a stabilization has to be achieved. In these usually complex malformations individual treatment is necessary. According to the rare cases in the literature and to our own experience a primary anterior decompression, followed by a most careful posterior stabilization seems to produce the most favourable results.

Craniovertebral junction malformations. Clinicoradiological findings, long-term results, and surgical indications in 63 cases

The fate of a series of 63 patients operated on between 1953 and 1979 was studied retrospectively to assess the efficacy of neurosurgical treatment in relieving symptoms associated with craniovertebral junction (CVJ) malformations. Fifty-eight patients underwent posterior cervicomedullary decompression, and the other five underwent transoral clivus-atlanto-odontoidectomy. Long-term results with the posterior approach showed that 50% of the patients benefited from surgery, 25% remained unchanged, and 25% continued to deteriorate or died. Patients with dorsal nervous tissue and/or meningeal anomalies, such as Arnold-Chiari malformation, hydrosyringomyelia, dural fibrous ring, or obstruction of the cisterna magna, did better than patients with ventral cervicomedullary indentation caused by a clivus-atlanto-odontoid bone complex. Anterior decompression is preferable to a posterior approach only if the CVJ malformation involves a ventral deformity in the absence of dorsal compression by soft tissue.

Craniocervical abnormalities. A comprehensive surgical approach

Guidelines are proposed for surgical management of symptomatic abnormalities of the craniocervical junction. Experience with 17 recent cases is described. Gas or metrizamide (Amipaque) myelograms with pluridirectional tomograms revealed the etiology and mechanisms of compression of the cervicomedullary junction, as well as its reducibility. Stabilization was the goal in treatment of reducible lesions. Decompression of the cervicomedullary junction was paramount in irreducible cases. Ventral compression was treated in nine patients by transoral transpalatine resection of the odontoid-clivus complex, and all nine improved. A posterior decompression was carried out when bone impingement was present from the dorsal aspect. Fusion was performed in cases in which stability was not achieved by either procedure.