Anatomy Atlas

Skull

Cranium
Also: Cranium · Neurocranium and viscerocranium
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The bones of the head — the neurocranium enclosing the brain and the viscerocranium forming the face. Pterion fractures, basilar skull fractures and infant fontanelles are the clinically important features.

Core anatomy

Location

Sits on the atlas (atlas and axis (C1 and C2)) at the atlanto-occipital joints.

Classification

Flat and irregular bones joined mainly by sutures (fibrous joints); the mandible is the only freely movable bone (see temporomandibular joint).

Key features & landmarks
  • Neurocranium (8 bones): frontal, 2 parietal, 2 temporal, occipital, sphenoid, ethmoid
  • Viscerocranium (facial skeleton): 2 nasal, 2 maxillae, 2 zygomatic, 2 lacrimal, 2 palatine, 2 inferior nasal conchae, vomer and the mandible
  • Sutures: coronal (frontal–parietal), sagittal (between the parietals), lambdoid (parietal–occipital), squamous (temporal–parietal)
  • Pterion: H-shaped junction of the frontal, parietal, temporal and greater wing of the sphenoid, about 3–4 cm above the zygomatic arch; the thinnest part of the lateral skull, overlying the anterior branch of the middle meningeal artery
  • Cranial fossae: anterior (frontal lobes; cribriform plate of the ethmoid), middle (temporal lobes, pituitary in the sella turcica; foramina rotundum, ovale, spinosum), posterior (cerebellum, brainstem; foramen magnum, internal acoustic meatus, jugular foramen, hypoglossal canal)
  • Key foramina: optic canal (CN II, ophthalmic artery); superior orbital fissure (CN III, IV, V1, VI); rotundum (V2); ovale (V3); spinosum (middle meningeal artery); jugular foramen (CN IX, X, XI, internal jugular vein); hypoglossal canal (CN XII); foramen magnum (medulla, vertebral arteries)
Relations

The dural venous sinuses groove the inner surface of the vault; the middle meningeal vessels groove the inner surface of the temporal and parietal bones.

Ossification

The vault forms by intramembranous ossification, the base by endochondral ossification. At birth the vault bones are separated by sutures and fontanelles: the anterior fontanelle (diamond-shaped) usually closes by about 18–24 months, the posterior fontanelle (triangular) by about 2 months. verify

Muscle attachments

Joints

Generated automatically from links in other entries.

Foramina of the cranial base (internal view)The floor of the cranial cavity seen from above, anterior at the top, divided into anterior, middle and posterior cranial fossae. Anterior fossa: the cribriform plate transmits the olfactory nerve fibers. Middle fossa: the optic canal transmits the optic nerve and ophthalmic artery; the superior orbital fissure transmits cranial nerves III, IV, the ophthalmic division of V and VI with the superior ophthalmic vein; the foramen rotundum transmits the maxillary nerve; the foramen ovale the mandibular nerve and lesser petrosal nerve; the foramen spinosum the middle meningeal artery. The foramen lacerum is filled with cartilage, and the internal carotid artery, emerging from the carotid canal in the petrous temporal bone, crosses above it. The sella turcica holds the pituitary gland. Posterior fossa: the internal acoustic meatus transmits the facial and vestibulocochlear nerves and labyrinthine artery; the jugular foramen transmits cranial nerves IX, X and XI and the internal jugular vein; the hypoglossal canal transmits cranial nerve XII; the foramen magnum transmits the medulla, the vertebral arteries and the spinal roots of the accessory nerve.Anterior fossaMiddle fossaPosterior fossaCribriform plateCN I (olfactory fibers)Optic canalCN II · ophthalmic arterySuperior orbital fissureCN III, IV, V1, VI · superior ophthalmic v.Foramen rotundumV2 (maxillary)Foramen ovaleV3 (mandibular) · lesser petrosal n.Foramen spinosumMiddle meningeal arteryForamen lacerumCartilage-filled · ICA crosses above itCarotid canal (dashed)Internal carotid a. · sympathetic plexusSella turcicaPituitary glandInternal acoustic meatusCN VII, VIII · labyrinthine arteryJugular foramenCN IX, X, XI · internal jugular veinHypoglossal canalCN XIIForamen magnumMedulla · vertebral aa. · spinal roots of CN XICranial base from above · anterior ↑Not to scale"Standing Room Only": V1 → Superior orbitalfissure, V2 → Rotundum, V3 → Ovale

Swipe sideways to see the whole diagram →

Foramina of the cranial base. Internal view from above, anterior at the top. Each foramen is drawn on both sides and labelled on one. The carotid canal runs inside the petrous bone (dashed) and opens at its apex, where the internal carotid artery crosses above the cartilage-filled foramen lacerum.
Original schematic, created for this atlas.
Lateral view of the skull with the frontal, parietal, temporal, sphenoid, zygomatic, maxilla and mandible tinted, and the coronal and squamosal sutures
Lateral view of the skull; the pterion lies where the frontal, parietal, temporal and sphenoid bones meet.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 188. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Anterior view of the skull showing the frontal bone, orbits with the superior and inferior orbital fissures, nasal cavity, maxillae and mandible
The skull from the front.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 190. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Epidural hematoma from pterion fracture PANCE

Mechanism / lesion

A blow to the side of the head fractures the thin pterion and tears the middle meningeal artery.

Classic presentation

Brief loss of consciousness, a lucid interval, then rapid deterioration (headache, vomiting, ipsilateral blown pupil, contralateral hemiparesis). CT shows a biconvex (lens-shaped) hematoma that does not cross sutures. Neurosurgical emergency.

Basilar skull fracture PANCE

Mechanism / lesion

Fracture through the skull base (often the petrous temporal bone or anterior cranial fossa) from significant head trauma.

Classic presentation

Raccoon eyes (periorbital ecchymosis), Battle sign (mastoid ecchymosis), hemotympanum, and CSF rhinorrhea or otorrhea; possible cranial nerve palsies (VII, VIII). Avoid nasogastric tubes and nasotracheal intubation (risk of intracranial passage).

Craniosynostosis

Mechanism / lesion

Premature fusion of one or more sutures; sagittal most common.

Classic presentation

Abnormal head shape (e.g. long narrow scaphocephaly with sagittal synostosis); may raise intracranial pressure. Distinguish from positional plagiocephaly.

Fontanelle as a clinical sign PANCE

Mechanism / lesion

The open anterior fontanelle reflects intracranial pressure and hydration in infants.

Classic presentation

Bulging → raised ICP (meningitis, hydrocephalus); sunken → dehydration. Delayed closure: hypothyroidism, rickets, raised ICP; early closure: craniosynostosis.

High-yield PANCE pearls

  • Lucid interval + biconvex bleed → epidural hematoma (middle meningeal artery at the pterion).
  • Raccoon eyes, Battle sign, hemotympanum, CSF leak → basilar skull fracture — no NG tube.
  • Bulging fontanelle = raised ICP; sunken = dehydration.
  • Anterior fontanelle closes by about 18–24 months; posterior by about 2 months.

Imaging anatomy

X-ray

Skull films are largely replaced by CT; still used in skeletal surveys for suspected child abuse.

CT

Non-contrast head CT is the first test in head trauma (fractures with bone windows, epidural/subdural hemorrhage). CT with 3-D reconstruction for craniosynostosis and facial fractures.

MRI

Brain parenchyma, skull base tumors and CSF leak localization (with CT cisternography).

Ultrasound

Cranial ultrasound through the open anterior fontanelle in neonates (intraventricular hemorrhage).

Key views & landmarks
  • Non-contrast head CT (brain and bone windows)

Physical exam

Surface landmarks

External occipital protuberance (inion), mastoid process, zygomatic arch, pterion (about two finger-breadths above the zygomatic arch and a thumb's breadth behind the frontal process of the zygomatic bone), nasion.

Palpation

In infants, palpate the anterior fontanelle (size, tension) with the baby upright and calm; palpate sutures for ridging. In trauma, palpate for steps and bogginess.

Strength / function testing

Inspect for raccoon eyes, Battle sign, CSF leak (clear fluid; "halo sign" on gauze) and hemotympanum on otoscopy.

Self-quiz

Q1.

A 19-year-old is hit on the side of the head with a baseball. He is briefly unconscious, then talks normally for 2 hours before becoming drowsy with a dilated right pupil. CT shows a biconvex hyperdense collection. Which vessel is most likely injured?

Show answer

B

A lucid interval with a biconvex (lentiform) extradural collection is an epidural hematoma, classically from the middle meningeal artery under the thin pterion. Subdural hematomas (crescent-shaped) come from bridging veins.

Q2.

After a car crash, a patient has bruising around both eyes and behind the ear, and clear fluid from the nose. What should be avoided?

Show answer

C

Raccoon eyes, Battle sign and CSF rhinorrhea indicate a basilar skull fracture. A nasogastric tube (or nasotracheal intubation) can pass through the fractured cribriform plate into the cranium; use the orogastric route.

Q3.

Which structure passes through the foramen spinosum?

Show answer

C

The middle meningeal artery enters the skull through the foramen spinosum. V3 passes through the foramen ovale, V2 through the foramen rotundum.

Q4.

After head trauma, a patient has bruising over the mastoid process. What is this sign called, and what does it suggest?

Show answer

B

Battle sign (mastoid ecchymosis), raccoon eyes, hemotympanum and CSF rhinorrhea or otorrhea suggest a basilar skull fracture. Avoid nasogastric tubes and nasotracheal intubation.

Q5.

A febrile 4-month-old has a tense, bulging anterior fontanelle while calm and upright. What does this indicate?

Show answer

E

A bulging fontanelle indicates raised intracranial pressure (meningitis, hydrocephalus); a sunken fontanelle suggests dehydration.

Flashcards

See also