The anatomic study of clival screw fixation for the craniovertebral region.

PURPOSE: To study the anatomic parameters related to clival screw and establish reference data concerning the craniovertebral fixation technique. METHODS: Morphometric measurement of the clivus and the surrounding anatomic structures were obtained on 41 dry bone specimens. Then, 2-D CT reconstruction of the craniovertebral region of 30 patients (19 men and 11 women, ranging in age from 20-64 years with an average age of 38.8 years) were performed to measure the safety range for a 3.5-mm screw placement. Nine entry points were evaluated. Finally, one male fresh cadaver specimen (age 46 years) was dissected to observe the craniovertebral region. RESULTS: The clivus faces the basilar artery, the V ~ XII cranial nerves, the pons, and ventral medulla oblongata at its intracranial surface. The longitudinal diameter of extracranial clivus was 25.87 ± 2.64 mm. The narrowest diameter of the clivus was 12.84 ± 1.08 mm, the distance between the left and right hypoglossal canal was 32.70 ± 2.09 mm at its widest part. The distance between the left and right structures, the maximum value was 49.31 ± 4.16 mm at carotid canal, the minimum value was 16.54 ± 2.04 mm at the occipital condyle. The measurement of clival screws placement simulation via 2-D CT reconstruction images shows the maximum upper insertion angle of three components the optimal entry points, the candidate points, the limit entry points was 130.19°, 125.23° and 85.72°, and the total mean screw length was 7.57, 10.13 and 15.6 mm at the vertical entry angle, respectively. CONCLUSIONS: Clival screw placement is a viable option for craniovertebral fixation. There is a safe scope for the screw length and angle of the screw placement. And, these parameters obtained in the present study will be helpful for anyone contemplating the use of clival screw fixation.

Comparative research of the thin transverse sectional anatomy and the multislice spiral CT on Pterygopalatine Fossa.

AIM: To explore a method to obtain sub-millimeter data of the thin transverse section of the pterygopalatine fossa (PPF), and to study the thin transverse sectional anatomy of the adult pterygopalatine fossa and its communicating structure for providing anatomic gist for the imaging diagnosis and minimal invasive operation when PPF diseased. MATERIAL AND METHODS: Two heads of adult cadaver without macroscopic trauma (four sides of PPF) were selected to observe. Images of 0.6 mm-thick multi-planar construction (MPR) were obtained with multislice spiral CT (MSCT) based on the superior orbitomeatal line. Then, the specimens were sliced into 0.1 mm serial section on the transverse plane with the computerized milling machine, the figures were taken with digital camera and the sectional data were stored in the computer. Lastly, the thin transversal section of PPF was investigated and compared with multislice spiral CT images acquired by MPR technique to explore and discuss the anatomy of the thin transverse section of the internal structure of PPF. RESULTS: PPF was divided into four portions: infrapterygopalatine portion, pterygopalatine ganglionic one, suprapterygopalatine one and roof of PPF according to the structural characteristics of the transverse section of PPF. The infrapterygopalatine portion communicated laterally with the infratemporal fossa through the pterygomaxillary fissure and communicated downwards with the oral cavity via palatine greater and lesser canals. The pterygopalatine ganglion was shown clearly in the pterygopalatine ganglionic portion, and its dimensions were 3.91x1.92 mm at the best layer. In the suprapterygopalatine portion, the sphenopalatine foramen and artery were obviously shown on the medial wall, while the palatovaginal canal and artery, the pterygoid canal and artery, and the foramen rotundum and maxillary nerve were shown from the inferiomedial to laterosuperior on the posterior wall. The vomerovaginal canal and artery were located at the slightly superior portion of the medial side of the palatovaginal canal. CONCLUSION: Figures of thin transverse section and multislice spiral CT have highly consistency for the display of PPF. Both of them can correctly identify the micro-structure, the complex relationship of the connectivity and the spatial localization in the narrow space of PPF. It can provide reference gist for the imaging diagnosis and minimal invasive operation.