Skull Base Surgery Atlas

An axial view of the skull through the level of the of the internal auditory canal and cerebellopontine angle.

Retro- labyrinthine, Trans- labyrinthine, Transcochlear Approaches

In the classical suboccipital approach bone is removed from the midline laterally until the first air cells are encountered. This often creates an opening located well posterior to the sigmoid sinus. When a suboccipital approach is used to expose the CPA, a relatively large amount of cerebellar retraction is necessary. With the retrosigmoid approach, where the opening created immediately adjacent to the sigmoid and transverse sinuses, much less cerebellar displacement is required. (SO, suboccipital; RS, retrosigmoid.)

Microsurgery of Acoustic Neuroma

(A) A schematic coronal view through the temporal bone illustrating the relationship between the undersurface of the temporal lobe and the roof of the petrous pyramid. An intracanalicular acoustic neuroma is present. Note that this often-used style of illustrating the inner ear in the coronal plane, which makes both the semicircular canals and cochlea visible through a single coronal slice, is inaccurate. The cochlea actually lies just beneath the floor of the middle cranial fossa.

Combined Craniotomies: Posterior & Middle Fossae

Completed exposure of a meningioma involving both the middle and posterior fossa by traversing Meckel’s cave via the combined retrolabyrinthine-middle fossa approach. The tumor spans from the entry zone of the audiovestibular and facial nerves (7,8) to the cavernous sinus (CS). Note the trochlear nerve on the tumor surface (4). The distil of the branches of the trigeminal nerve can be seen (V2, V3). The posterior retractor is on the cerebellum (Cb). The superior retractor is on the temporal lobe (TL). The curled dural flap containing the endolymphatic sac (ES) overlies the petrous portion of the temporal bone containing the semicircular canals. All three segments of the brainstem are visible: medulla (M), pons (P), midbrain (MB). The edges of the divided tentorium (T) can be seen anteriorly and posteriorly. (for details of the microsurgical exposure, see “Combined Craniotomies of the Posterior and Middle Fossae).

Meningioma via Combined Approach

Anatomical overview of the jugular foramen region and its neurovascular relationships. (9, glossopharyngeal nerve; 10, vagus nerve; 11, spinal accessory nerve; 13, hypoglossal nerve.)

Use of Endoscopes in Skull Base Surgery

Schematic illustration of the major arterial branches in the cerebellopontine angle. (IAA, internal auditory artery; SCA, superior cerebellar artery; AICA, anterior inferior cerebellar artery; PICA, posterior inferior cerebellar artery.)

Vascular Considerations in Lateral Skull Base Surgery

$Fractures through the petrous pyramid may result from either posterior or lateral blows to the head. The skull base fractures more easily when struck from the side, on the thin temporal squamosa, than posteriorly on the thick occipital bone. Fractures resulting from temporal blows tend to propagate medially along a course parallel to the long axis of the petrous pyramid and thus are termed longitudinal. Strong occiptal blows characteristically produce a fracture which disrupts the foramen magnum ring and then propagates anteriorly across the petrous pyramid art right angles to its long axis. These are termed transverse fractures.$

Fractures of the Cranial Base

$Encephaloceles of the temporal bone most commonly occur through the floor of the middle cranial fossa into the epitympanum or mastoid. Most frequently, they are traumatic in origin, arising either due to cranial base fracture or after iatrogenic injury sustained during mastoid surgery. Spontaneous meningoceles and encephaloceles also occur, presumably due to prominent arachnoid granulations that penetrate the eggshell-thin tegmen mastoideum or tympani. Chronically increased intracranial pressure may play a role in such cases.$