Odontoid process hypoplasia and bipartite atlas associated with atlanto-axial instability / Hipoplasia do processo odontóide e atlas bipartido associado a instabilidade atlanto-axial / Hipoplasia de la apófisis odontoide y atlas bipartito asociado con inestabilidad atlantoaxial

ABSTRACT Surgical treatment of craniocervical junction pathology has evolved considerably in recent years with the implementation of short fixation techniques rather than long occipito-cervical fixation (sub-axial). It is often difficult and sometimes misleading to determine the particular bone and vascular features (high riding vertebral artery, for instance) using only the conventional images in three orthogonal planes (axial, sagittal and coronal). The authors describe a rare clinical case of congenital malformation of the craniovertebral junction consisting of hypoplasia/agenesis of the odontoid process and bipartite atlas associated with atlantoaxial instability which was diagnosed late in life in a patient with a previous history of rheumatologic disease. The authors refer to the diagnostic process, including new imaging techniques, and three-dimensional multiplanar reconstruction. The authors also discuss the surgical technique and possible alternatives.

RESUMO O tratamento cirúrgico da patologia da charneira crânio-cervical tem evoluído consideravelmente nos últimos anos com a implementação de técnicas de fixação curta em detrimento de longas fixações occipito-cervicais (sub-axiais). Frequentemente é difícil e por vezes enganador determinar as variações ósseas e vasculares (artéria vertebral high-riding p.e.) apenas pelas imagens convencionais em três planos ortogonais (axial, sagital e coronal). Os autores descrevem um caso clínico raro de malformação congénita da charneira crânio-cervical constituída por hipoplasia/agenésia da odontoide e atlas bipartido, associado a instabilidade atlanto-axial e diagnosticado tardiamente em doente com antecedentes reumáticos prévios. Descreve-se o processo diagnóstico, incluindo novas técnicas de imagiologia e de reconstrução multiplanar tridimensional. Discute-se a técnica cirúrgica utilizada e possíveis alternativas.

RESUMEN El tratamiento quirúrgico de la patología de la región craneocervical ha evolucionado considerablemente en los últimos años con la aplicación de técnicas de fijación cortas en lugar de fijación occipito-cervical larga (sub-axial). A menudo es difícil y hasta engañoso determinar las características óseos y vasculares (arteria vertebral high-riding, por ejemplo) usando sólo imágenes convencionales en tres planos ortogonales (axial, sagital y coronal). Los autores describen un caso clínico poco frecuente de malformación congénita de la unión craneocervical que consiste en la hipoplasia/agenesia de la apófisis odontoides y atlas bipartito, asociado con la inestabilidad atlantoaxial, diagnosticado tardiamente en pacientes con enfermedades reumatológicas previas. Los autores relatan el proceso de diagnóstico, incluyendo nuevas técnicas de imagen y la reconstrucción multiplanar tridimensional. Los autores también discuten la técnica quirúrgica y las posibles alternativas.

"Two-step" technique with OsiriX™ to evaluate feasibility of C2 pedicle for surgical fixation.

BACKGROUND: Surgical treatment of craniovertebral junction pathology has evolved considerably in recent decades with the implementation of short atlanto-axial fixation techniques, notwhithstanding increasing neurovascular risks. Also, there is strong evidence that fixation of C2 anatomical pedicle has the best biomechanical profile of the entire cervical spine. However, it is often difficult and misleading, to evaluate anatomical bony and vascular anomalies using the three orthogonal planes (axial, coronal, and sagittal) of CT. OBJECTIVES: The authors describe an innovative and simple technique to evaluate the feasibility of C2 pedicle for surgical screw fixation using preoperative planning with the free DICOM (Digital Imaging and Communications in Medicine) software OsiriX™. MATERIALS AND METHODS: The authors report the applicatin of this novel technique in 5 cases (3 traumatic, 1 Os Odontoideum, and 1 complex congenital malformation) collected from our general case series of the Department in the last 5 years. RESULTS: In this proof of concept study, the pre-operative analysis with the two-step tecnique was detrimental for choosing the surgical tecnique. Detailed post-operative analysis confirmed correct position of C2 screws without cortical breach. There were no complications or mortality reported. CONCLUSION: This two-step technique is an easy and reliable way to determine the feasibility of C2 pedicle for surgical fixation. The detailed tridimensional radiological preoperative evaluation of craniovertebral junction anatomy is critical to the sucess and safety of this surgeries, and can avoid, to certain degree, expensive intra-operative tridimensional imaging facilities.