The Relationships between Asterion, the Transverse-Sigmoid Junction, the Superior Nuchal Line and the Transverse Sinus in Thai Cadavers: Surgical Relevance.

Background: Anatomical localization of the venous sinuses in the posterior cranial fossa is important to preventing inadvertent venous sinus injury during surgical approaches to the area. Identification of surface landmarks related to these structures is useful in planning such approaches. Objective: To identify the positions of the asterion and the superior nuchal line for localization of the venous sinus in the posterior fossa. Material and Method: Twenty fresh cadaveric heads, yielding 40 sides, were used. The vessels were injected with colored silicone. The soft tissues were removed to expose the posterior cranium, from inion to the foramen magnum and laterally to the mastoid process. Using digital calipers, the relationship of asterion to the transverse-sigmoid sinus junction was determined and the distance from the highest superior nuchal line to the nearest transverse sinus was measured. Results: Asterion was located in 82.5% of the cadavers on the right side and 85.0% on the left side. The most common asterion position was at the junction of the transverse and sigmoid sinuses (67.5%), of which 5.0% were superior to the transverse-sigmoid junction, 2.5% inferior to the transverse-sigmoid junction and 7.5% medial to the transverse-sigmoid junction, at the transverse sinus. The superior nuchal line was identified in all cadavers. The most common position was inferior to the transverse sinus (60.0%) at an average distance of 8.55 mm 35.0% were at the same level as the transverse sinus and 5.0% were superior to the transverse sinus at an average distance of 2.14 mm. Conclusion: A burr hole inferior-medial to asterion can expose the posterior fossa dura with the least risk. The superior nuchal line is always identifiable and relatively close to the transverse sinus. A burr hole more than 3 mm inferior to the superior nuchal line can expose the posterior fossa dura with the least risk.

Incidence and variation of interpretably bone (os incae) in northeastern Thailand.

BACKGROUND: The squamous segment of occipital bone consists of cartilaginous and membranous origin. The cartilaginous part develops to supra-occipital bone. The membranous part has three primary ossification centers on each side. The first pair ossification center lies above the cartilaginous part between the superior nuchal line and the highest nuchal line and fuse with the cartilaginous part to form a supra-occipital segment of occipital bone. The second and third pairs have two nuclei each forming lateral and medial plates. All of these ossification centers fuse to form squamous segments of occipital bone. The fusion failure between ossification centers of second and third pair nuclei with each other or supra-occipital segment causes separated bone(s) called interparietal bone(s) or os incae. The interparietal bone should be differentiated from Wormian (intrasutural) bone. The incidence from various studies ranges from 0.37% to 9.50% of the population. OBJECTIVE: To study the incidence and variation of interparietal bone in Northeastern Thailand as compared with other studies. MATERIAL AND METHOD: A total of 400 Thai native skulls (276 male and 124 female) from the collection of Anatomical Museum of the Faculty of Medicine Khon Kaen University aged from 16 to 93 years old were examined by naked eye and photographed. Wormian bone was excluded by shape and site. The statistical method used was percentage of relative frequency. RESULTS: The incidence of interparietal bone in Northeastern Thailand is 7.25% (29 from 400). Males have a two times higher incidence rate than females, (8.33% versus 4.84%). Eleven patterns of interparietal bone were found. Fusion failure of a third pair ossification center is more common than second pair CONCLUSION: Knowledge of interparietal bone is useful for neurosurgeons and radiologists to avoid missed diagnosis of skull fracture. Presented interparietal bone may cause difficulty in surgery of occipital and parietal bone. Forensic scientist can use interparietal bone for personal identification.

Supramastoid crest, safety landmark for craniotomy?

BACKGROUND: Bony landmarks are important in identifying and avoiding various structures, and thus, decreasing surgical morbidity. Knowledge of frontal bone was studied to help surgeons with safe craniotomy as temporooccipital region study was rare. OBJECTIVE: To identify usefulness of supramastoid crest and relationship to venous and Labbe's vein. MATERIAL AND METHOD: Twenty fresh cadaveric heads, the vessels were injected with colorized silicone, were studied on both sides, yielded 40 sides. The relationship of the supramastoid crest to the transverse, sigmoid sinus, Labbe's vein was also determined and measured. The following distances were measured utilizing the digital caliper for all measurements. RESULTS: Supramastoid crest was found in all cadavers (100%) and skull opened along supramastoid crest 100% safe from injury to venous sinus. Anterior border of supramastoid crest was close in relation to middle cranialfossa floor, 85% on right side and 90% on left side and the same level of middle cranial. The authors defined supramastoid point with turning of supramastoid crest and found distance from supramastoid point to nearest venous sinuse (always transverse sinus) 1.0-22.41 mm in range and average 12.94 mm on right side and 11.87 mm on left side. The last distance, from supramastoid point to nearest Labbe's vein, was measured and found to be 5.94-24.97 mm in range and average 17.23 mm on both sides. CONCLUSION: Supramastoid crest is bony landmark and easy to identify in the adult cadaver and craniotomy along supramastoid crest and always safe from injuring the venous sinus and Labbe s vein. 87.5% anterior border of supramastoid crest is the same level for middle cranial fossa floor.