CorpusHuman Anatomy
SkeletalRegion

Cranial fossae and foramina of the skull base

Fossae cranii

Also known as: cranial base, skull base, foramina of the skull, anterior cranial fossa, middle cranial fossa, posterior cranial fossa

The floor of the cranial cavity is stepped into anterior, middle and posterior cranial fossae that cradle the brain. Their foramina transmit the cranial nerves and the major vessels of the head.

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Overview

The anterior cranial fossa (frontal orbital plates, cribriform plate of the ethmoid, lesser wings and front of the sphenoid body) supports the frontal lobes and olfactory bulbs. It is separated from the middle fossa by the sharp posterior edges of the lesser wings (sphenoidal ridges).

The butterfly-shaped middle cranial fossa has a narrow central part (sella turcica with the pituitary) and two deep lateral parts (greater wings of the sphenoid, squamous and petrous temporal bones) lodging the temporal lobes. It contains most of the important foramina. Its posterior limit is the superior border of the petrous temporal bone and the dorsum sellae.

The posterior cranial fossa, the largest and deepest (occipital bone, petrous and mastoid temporal, dorsum sellae and clivus), contains the cerebellum, pons and medulla, roofed by the tentorium cerebelli. It is pierced by the foramen magnum, the internal acoustic meatus, the jugular foramen and the hypoglossal canal.

Location

Internal surface of the cranial base.

Parts & subdivisions

  1. Cribriform plate foramina (anterior fossa)
    Olfactory nerve filaments (CN I).
  2. Optic canal (middle fossa)
    Optic nerve (CN II), ophthalmic artery.
  3. Superior orbital fissure (middle fossa)
    CN III, IV, V1 (lacrimal, frontal, nasociliary), VI; superior ophthalmic vein; sympathetic fibres.
  4. Foramen rotundum (middle fossa)
    Maxillary nerve (V2).
  5. Foramen ovale (middle fossa)
    Mandibular nerve (V3), accessory meningeal artery, lesser petrosal nerve, emissary vein.
  6. Foramen spinosum (middle fossa)
    Middle meningeal artery and vein, meningeal branch of V3.
  7. Foramen lacerum (middle fossa)
    Filled with cartilage in life; the internal carotid artery passes across its upper end; the greater petrosal nerve joins the deep petrosal nerve here.
  8. Carotid canal (middle fossa)
    Internal carotid artery and its sympathetic plexus.
  9. Internal acoustic meatus (posterior fossa)
    Facial nerve (CN VII), vestibulocochlear nerve (CN VIII), labyrinthine artery.
  10. Jugular foramen (posterior fossa)
    Glossopharyngeal (IX), vagus (X) and accessory (XI) nerves; sigmoid sinus → internal jugular vein; inferior petrosal sinus.
  11. Hypoglossal canal (posterior fossa)
    Hypoglossal nerve (CN XII).
  12. Foramen magnum (posterior fossa)
    Medulla/spinal cord and meninges, vertebral arteries, anterior and posterior spinal arteries, spinal roots of CN XI.
  13. Stylomastoid foramen (external base)
    Exit of the facial nerve (CN VII) to the face.

Function

  • Support the lobes of the brain in three tiers
  • Transmit cranial nerves and vessels between the cranial cavity and the head and neck

Clinical significance

Jugular foramen (Vernet) syndrome

A lesion at the jugular foramen (e.g. glomus tumour) paralyses CN IX, X and XI: loss of gag reflex, dysphagia, hoarseness with uvular deviation away from the lesion, and weakness of trapezius and sternocleidomastoid.

Anterior cranial fossa fracture

Periorbital "raccoon eyes", CSF rhinorrhoea and anosmia; nasogastric tubes are contraindicated because they may pass into the cranial cavity.

Middle cranial fossa fracture

May involve the petrous temporal bone (haemotympanum, CSF otorrhoea, facial nerve palsy, deafness) and is accompanied by Battle sign.

Mnemonics

Cranial nerves through the posterior fossa

Internal acoustic meatus 7 & 8; jugular foramen 9, 10, 11; hypoglossal canal 12 — "7-8 hear, 9-10-11 jugular, 12 alone".

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.