Pulmonary oedema after venous air embolism during craniotomy:

Mastoid emissary foramina: an anatomical morphological study with discussion on their evolutionary and clinical implications

The identification of mastoidal emissary veins is of importance in the neurosurgical practice to diagnose abnormal and normal structures. In the present study, the objectives were to estimate the prevalence rate of mastoidal emissary foramina in the temporal bones of the adult skull and to study their number and morphology. The present study included 48 adult human skulls which were obtained from the gross anatomy laboratory of our institution. The mastoid parts of 96 temporal bones were macroscopically observed for the prevalence, number and morphology of the emissary foramina. It is observed that, the mastoidal emissary foramen was present in 88 temporal bones (91.7%) of our specimens. The foramen was observed single in 60 temporal bones (62.5%), double in 22 bones (22.9%), and triple in 6 temporal bones (6.2%). The mastoidal emissary foramen was absent in 8 (8.3%) temporal bones. The foramen was bilaterally absent in 3 (3.1%) skulls. It was unilaterally absent in 2 (2.1%) skulls and both were on the left side. The mastoidal emissary vein is prevalent in a large number (91.7%) of cases. It was observed that the accessory mastoidal emissary foramina were present in 29.1% of cases. Recognition of the mastoid emissary veins and accessory mastoid emissary veins during the otologic surgery is critical to avoid the significant bleeding. In the neurosurgical practice, the knowledge is important due to variability in the number of mastoidal emissary veins and their connection to the venous sinuses.

Anatomy of the mastoid emissary vein and venous system of the posterior neck region: neurosurgical implications

OBJECTIVE

The superficial venous system of the posterior neck (suboccipital venous plexus) is a potential source of complications from bleeding and air embolism. Because there is little information available about this in the literature, an anatomic study of the superficial posterior neck venous system and a morphometric analysis of the mastoid emissary vein (MEV) complex were undertaken. Both surgical and endovascular implications were considered.

METHODS

The posterior craniocervical regions of 15 silicon-injected human cadaveric specimens were dissected. The patterns and variances of venous anatomy were observed. Distances between fixed bony landmarks were measured with a caliper.

RESULTS

The suboccipital venous plexus, which forms a complex venous network located between the posterior muscular layers of the neck, drains to the anterior vertebral vein and deep cervical vein. The MEV connects this plexus to the sigmoid sinus. Its average diameter was 2.15 mm, and it was located a mean of 21.14 mm from the asterion and a mean of 33.65 mm from the mastoid tip. However, the size of the MEV complex varied considerably.

CONCLUSION

The suboccipital venous plexus in the posterior neck region may be very large. The size of the veins in the plexus varies, but the drainage pattern remains consistent. The plexus is a potential source of intense bleeding and air embolism during posterior fossa approaches. The risks are greatest for lateral surgical approaches, as a result of the anatomic position of the venous system. The described measurements can be used to approach the MEV in endovascular procedures that involve the sigmoid sinus.