The posterior cranial fossa is the deepest and most inferior of the three cranial fossae, housing the cerebellum, pons, medulla, and the origin of cranial nerves V-XII. It is bounded anteriorly by the clivus and petrous ridges, laterally by the mastoid and petrous temporal bones, and posteriorly by the occipital bone. Key foramina include the internal acoustic meatus (CN VII, VIII), jugular foramen (CN IX, X, XI), hypoglossal canal (CN XII), and foramen magnum.
The posterior cranial fossa contains the life-critical brainstem and cerebellum, making posterior fossa pathology high-stakes. Space-occupying lesions produce herniation through the foramen magnum. Posterior fossa tumours include acoustic neuromas, meningiomas, cerebellar astrocytomas, medulloblastomas, and ependymomas. Surgical approaches include the retrosigmoid craniotomy, the translabyrinthine approach (through the mastoid and labyrinth), and the far lateral approach for foramen magnum lesions. The dural sinuses in the posterior fossa — transverse, sigmoid, and occipital — must be preserved during craniotomy.
Hypertensive haemorrhage into the posterior fossa, most commonly the cerebellar hemisphere, rapidly produces obstructive hydrocephalus from aqueduct compression and direct brainstem compression, requiring emergency posterior fossa decompression and haematoma evacuation.
Posterior fossa mass lesion or diffuse cerebral swelling produces downward herniation of the cerebellar tonsils through the foramen magnum, compressing the medulla and causing sudden respiratory arrest, prevented by urgent posterior fossa decompression and CSF diversion.
