Twenty Intracranial Skull Base Variations in the Same Specimen

Abstract

Anatomists and clinicians often encounter single bony anatomical variations in dry skulls and on imaging. However, a constellation of 20 such variants some that, to our knowledge, have not been previously described is noteworthy. Here, we describe an adult skull with multiple bony variations, and these are detailed and discussed. These included clival canals, an interclinoid bar with resultant foramen at the uppermost aspect of the clivus, middle clinoid process, posterior petroclinoid ligament, pterygoalar plate, septated hypoglossal canal, foramen through the anterior clinoid process, septated foramen ovale, shortened superior orbital fissure, and crista muscularis. Knowledge of individual differences in the structure of the skull may be of use to both anatomists and clinicians in the treatment of intracranial procedures as well as cranial imaging studies. Taken together, such a unique specimen is of archival value.

Keywords: anatomy; cadaver; cranium; intracranial; skull; variations.

Figure 1. Left: Note the left anterior clinoid process (AC) with unusual foramen passing through it (black arrow). The optic foramen is seen just medial to this as well as the bony bar (red arrow) between the posterior clinoid processes with resultant foramen. The shortened left superior orbital fissure (black/white arrow) and ossified petroclinoid ligament (green arrow) are seen. Two of the large clival canals are seen at the white/black arrow and white arrow. Middle: A metal wire is inserted into the foramen formed by the interclinoid bony bar. Large and small clival canals are seen at the arrows. Right: Inferior view noting the crista muscularis (black arrows), and two clival canals that have pierced the bone (yellow arrows).

Figure 2. Lateral view noting the ossified posterior petroclinoid ligament (left vertical white arrow), foramen (horizontal white arrow) formed by the interclinoid bony bar, middle clinoid process (yellow arrow) with resultant caroticoclinoid foramen (*).

A foramen is noted traveling through the left anterior clinoid process (right vertical white arrow). Note the optic foramen (OF).

Figure 3. Left: Floor of the left middle cranial fossa noting the foramen rotundum (FR), foramen spinosum (FS), and septated foramen ovale (arrow). Middle: Following removal of the zygomatic arch, the large plate of bone extending off of the pterygoid process is easily seen. Right: red tubing is inserted through the lateral part of the septated foramen ovale and a blue wire is placed into the unnamed foramen. Note the foramen spinosum (FS) and foramen ovale are both integrated into this bony sheet of bone.

Note the foramen ovale (black arrow), foramen spinosum (blue arrow), and unnamed foramen (green arrow).

Figure 4. Left: View into the posterior cranial fossa. Middle: Inferior view of the left skull base noting the foramen ovale (FO), mastoid process (MP), paramastoid process (PMP), and the external septation of the jugular foramen with three compartments as shown by the red, green, and blue wires. Right: View of the right posterior cranial fossa noting the internal acoustic meatus (IAM), jugular foramen (JF), and septated hypoglossal canal (white arrow).

Note the internal acoustic meatus (IAM), hypoglossal canal (HC), foramen magnum (FM), and the more internal septation within the left jugular foramen (arrow). Also note the bony canal (black arrow) formed for the inferior petrosal sinus, osteophyte (red arrow) protruding toward the groove for the sigmoid sinus, and large granular foveola (blue arrow) at the junction of the grooves for the transverse and sigmoid sinuses.