Makindo Medical Notes

Skull Anatomy

The skull provides structural protection for the brain, support for the face, and passage for cranial nerves and major vessels. For clinical practice, skull anatomy is best understood by combining bones, named foramina, transmitted structures, and embryological development. This integrated approach helps explain fracture patterns, cranial nerve deficits, and congenital abnormalities.

🧩 Bones of the Skull

The skull is divided into the neurocranium (protecting the brain) and the viscerocranium (forming the facial skeleton). The neurocranium consists of eight bones forming the cranial vault and base, while the facial skeleton comprises fourteen bones.

• Neurocranium: Frontal, parietal (×2), temporal (×2), occipital, sphenoid, ethmoid
• Viscerocranium: Maxilla (×2), zygomatic (×2), nasal (×2), lacrimal (×2), palatine (×2), inferior nasal concha (×2), vomer, mandible

🕳️ Skull Base Foramina – High-Yield Anatomy

The skull base contains multiple foramina that transmit cranial nerves and major vessels. Lesions at the skull base often produce characteristic clusters of cranial nerve deficits, making knowledge of these foramina clinically essential.

Anterior Cranial Fossa

• Cribriform plate (ethmoid): Olfactory nerve (CN I) → anosmia, CSF rhinorrhoea if fractured
• Optic canal (sphenoid): Optic nerve (CN II), ophthalmic artery

Middle Cranial Fossa

• Superior orbital fissure: CN III, IV, V1, VI + sympathetic fibres
• Foramen rotundum: Maxillary nerve (V2)
• Foramen ovale: Mandibular nerve (V3)
• Foramen spinosum: Middle meningeal artery (rupture → extradural haematoma)

Posterior Cranial Fossa

• Internal acoustic meatus: CN VII, VIII
• Jugular foramen: CN IX, X, XI + internal jugular vein
• Hypoglossal canal: CN XII
• Foramen magnum: Medulla, vertebral arteries, spinal root of CN XI

🧠 Relations & Clinical Correlations

The skull base is closely related to the brainstem, pituitary gland, cavernous sinus, and major vascular structures. This explains why skull base pathology can produce mixed cranial nerve palsies and autonomic symptoms. For example, cavernous sinus disease may affect eye movements, corneal sensation, and sympathetic fibres simultaneously.

• Cavernous sinus: CN III, IV, V1, V2, VI + internal carotid artery
• Middle meningeal artery runs deep to pterion
• Jugular foramen lesions → dysphagia, hoarseness, shoulder weakness

🧬 Development of the Skull

The skull develops from both neural crest cells and mesoderm, using two distinct ossification processes. The cranial vault forms mainly by intramembranous ossification, allowing postnatal brain growth, while the skull base forms by endochondral ossification, creating a rigid platform for the brain.

• Intramembranous: Flat bones of skull vault (fontanelles allow growth)
• Endochondral: Skull base (sphenoid, occipital)
• Premature