Function
What it does: Encloses and protects the brain; houses the special sense organs; provides attachment for muscles of mastication and facial expression.
Anatomy
Where to spot it: 22 bones total: 8 cranial (frontal, 2 parietal, 2 temporal, occipital, sphenoid, ethmoid) + 14 facial. Joined by sutures: coronal, sagittal, lambdoid, squamous. Major foramina: foramen magnum (medulla, vertebral arteries, CN XI), optic canal (CN II, ophthalmic artery), superior orbital fissure (CN III, IV, V1, VI), foramen rotundum (V2), foramen ovale (V3), foramen spinosum (middle meningeal artery), jugular foramen (CN IX, X, XI; IJV), hypoglossal canal (CN XII).
Development
How it forms: Calvaria forms by intramembranous ossification; base of skull by endochondral ossification. Anterior fontanelle closes by 18–24 months; posterior by 1–3 months.
Basilar skull fracture → 'raccoon eyes' (periorbital), Battle sign (mastoid bruising), CSF rhinorrhea/otorrhea (halo sign on gauze). Pterion is the thinnest part of the skull — fracture lacerates the middle meningeal artery → epidural hematoma (lucid interval, lens-shaped on CT). Subdural hematoma = bridging vein tear, crescent-shaped, crosses sutures, common in elderly/alcoholics. Premature suture closure = craniosynostosis (e.g. scaphocephaly from sagittal suture fusion). Cribriform plate fracture → anosmia + CSF rhinorrhea (CN I). High-yield
Middle meningeal artery is a branch of the maxillary artery (from external carotid). Foramen magnum syndrome: tonsillar herniation → respiratory arrest. Le Fort fractures (I, II, III) classify maxillofacial trauma — always test for CSF leak. Mnemonic
Cranial foramina contents: 'Standing Room Only' — Superior orbital fissure (V1), foramen Rotundum (V2), foramen Ovale (V3).
