Radiological and Morphometric Study of the Emissary Foramens and Canal in the Posterior Cranial Fossa of the Human Skull with Its Neurosurgical Significance

Abstract

Objective The posterior condylar canals (PCCs), posterior condylar veins (PCVs), occipital foramen (OF), and occipital emissary vein (OEV) are potential anatomical landmarks for surgical approaches through the lateral foramen magnum. We performed the study to make morphometric and radiological analyses of the various emissary foramens and vein in the posterior cranial fossa. Methods Morphometric study were performed on 95 dry occipital bones and radiological analyses on computed tomography (CT) angiography images of 150 patients. The number of OFs on both sides was recorded and PCC length and mean diameters of the internal and external orifices of PCC were measured for bony specimens. Prevalence of PCV and PCV size was investigated using CT angiography. Results Mean PCC length was higher in the left side (9.85 ± 2.5). Mean diameter of the internal orifice and the external orifice diameter were almost the same. The majority of PCCs (75-79.33%) had 2 to 5 mm diameter; only 4 to 9.2% were small in size (< 2 mm). In CT angiography, PCV was not identified in 23 (15.33%) patients. PCVs were located bilaterally in 105 (70%) and unilaterally in 22 (20.5%) patients. Only 11.3% of PCVs were large in size (> 5 mm), 80% of PCVs were medium sized (2-5 mm), and 8.6% were small sized (< 2 mm). Conclusion Normal values of OF, PCC, PCV, and OEV could serve as a future reference for the understanding of the physiology of craniocervical venous drainage, which is necessary to avoid surgical complications and can also serve as a guide to surgical interventions for pathologies of the posterior cranial fossa, such as tumors and injuries.

Keywords: angiography; computed tomography; emissary vein; occipital foramen; posterior condylar canal; posterior condylar vein.

Fig. 1

Occipital foramen (OF) in the midline ( A ), OF bilateral ( B ), OF unilateral ( C ), OF absent ( D ), and OF bilateral to midline with canal ( E ).

Fig. 2

Computed tomography (CT) angiography of posterior condylar canal (PCC) and posterior condylar vein (PCV). Three-dimensional volume-rendered image in posterior view shows bilateral Posterior condylar foramens and the PCVs exiting from PCCs ( black arrows ).

Fig. 3

Bilateral posterior condylar canals appearing as simple foramen with no variations in perforation or bony spicule or canal ( black arrows ).

Fig. 4

Computed tomography angiography of posterior condylar foramen, posterior condylar canal (PCC), and posterior condylar vein (PCV). A sagittal multiplanar reformatted image demonstrates the PCV in the PCC ( black arrow ) arising from the jugular bulb ( black arrowhead ) draining into the deep cervical vein and the horizontal portion of the vertebral venous plexus.

Fig. 5

Computed tomography angiography of the occipital foramen (OF). Three-dimensional volume-rendered image in posterior view ( A ) shows small OF in the midline ( arrow ) and ( B ) bilateral posterior condylar foramens ( arrow ).