Dissection 4 - Scalp and Cranial Meninges

Dissection Guide

Layers of the Scalp

• S: Skin

• C: (Dense) CT

• A: Aponeurosis

• L: Loose CT

• P: Pericranium

• M. of facial expression and intervening aponeurosis

  • Epicaranial apoenurosis: Frontalis and occipitalis

  • Galae aponeurotics

• Branches of ICA and ICA that anastamose in the scalp

  • ICA: Supratrochlear and supraorbital a.

  • ECA: Superficial temporal, posterior auricular, occipital aa.

  • Blood vessels lie in the dense CT

    • Lots of bleeding when lacerated because rich anastomotic network

• Sutures: Sagittal and coronal

  • Sagittal runs “vertically”

  • Coronal runs “horizontally” in the anterior

• Role of arachnoid villi in circulation of CSF: Pierce dura mater, allowing CSF to enter superior saggital sinus

Hematomas: Epidural vs. Subdural

• Epidural hematoma: has a clear boundary, caused by severed middle meningeal a.

  • Rapid blood accumulation, compression of the brain and neurologic problems

• Subdural hematoma: diffused boundaries, caused by torn cerebral v.

  • Displacement and neurological symptoms are slow

Venous Sinuses

• Diaphragma sellae: Membrane covering sella turcica

  • Infundibulum of pituitary gland pierces through

  • Cavernous sinus runs laterally

• Can see dilations of superior sagittal, transverse and superior petrosal sinuses on cranial bone

  • Venous drainage pathways

    • Inferior sagittal sinus → IJV: Inferior sagittal → Straight → Confluence of sinuses → Transverse → Sigmoid → IJV

    • Superior sagittal sinus → IJV: Superior sagittal → Confluence of sinuses → Transverse → Sigmoid → IJV

    • Cavernous sinus → IJV: Cavernous → Superior petrosal → Sigmoid → IJV

    • Superior petrosal sinus → IJV: Superior petrosal → Sigmoid → IJV

    • Inferior petrosal sinus → IJV: Inferior petrosal → IJV

Identifying CN and Others in the Cranium

• Olfactory bulb + tracts lie on cribrioform plate of ethmoid

• Optic n. (CN II) → Enter cranium via optic canal → Optic foramen → Optic chiasm

• ICA → Ophthalmic a. → Optic canal

  • ICA enters through the carotid canal

• Oculomotor n. (CN III) → Pierce dura forming roof of each cavernous sinus → Superior orbital fissure (to enter orbit)

• Trochlear n. (CN IV) → Anteromedial to CN V as it pierces dura to enter cavernous sinus → Superior orbital fissure (to enter obit)

• Trigeminal n. (CN V) → Trigeminal ganglion within trigeminal impression

• Abducens n. (CN VI) → Pierce dura overlying the clivus

  • Ascend clivus → Toward petrous apex → Deep to petrosphenoidal ligament → Cavernous sinus → Superior orbital fissure

• Facial n. (CN VII) → Internal auditory meatus → Stylomastoid foramen

• Vestibulocochlear n. (CN VIII) → Internal auditory meatus → Cochlea/Vestibule

• Glossopharyngeal n. + Vagus n. + Spinal accessory n. → Jugular foramen

• Spinal accessory n. has spinal root (see entering skull through foramen magnum)

• Hypoglossal n. → Hypoglossal canal

• Maxillary a. → Foramen spinosum → Middle meningeal a.

• Function and clinical significance of anastamoses between venous dural sinuses and internal vertebral venous plexus:

  • Allow bidirectional blood flow; alternate route for venous return from the brain (in case of blockage)

• Vertebral a.: Pair of a. entering foramen magnum → Basilar a. (ascends clivus) → Circle of Willis

• Dural venous sinus

Cavernous sinus

• N. within sinus: CN III, IV, V1, and V2

Bolded Terms

Abducens n.

• CN VI

• Innervates lateral rectus

• Ascend clivus → Toward petrous apex → Deep to petrosphenoidal ligament → Cavernous sinus → Superior orbital fissure

Accessory n.

• CN XI

• Innervates trapezius and SCM

• Enters jugular foramen with roots extending from foramen magnum

Anterior cranial fossa

Arachnoid fovea

• Indentations along sagittal sulcus where arachnoid granules sit in

• Allow CSF to drain from the subarachnoid space into the venous system

Basilar a.

• L and R vertebral a. → Basilar a. (ascends clivus)

• Part of circle of willis

Calvaria

Cavernous sinus

• Cavernous → Superior petrosal → Sigmoid → IJV

• Drains blood from face/orbit/infratemproal fossa

Cerebral v.

Clinoid processes (anterior and posterior)

• “slide” leading into foramen magnum

Confluence of sinuses

• Where superior sagittal, transverse, straight, and occipital sinus meet

Coronal suture

• Suture separating frontal bone from parietal bones

Cribiform plate of ethmoid

• Where the olfactory bulb and tract lay

Diaphragma sellae

• Membrane covering sella turcica

Diploe

• Spongy bone in the cranium

Dural venous sinuses

• Dilations between periosteal and meningeal layers in dura mater

• Drains deoxygenated blood, waste, and CSF into systemic circulation

Facial n.

• CN VII

• Internal auditory meatus → Stylomastoid foramen

Falx cerebri

• Dura that separates L and R hemispheres

Foramen magnum

• Where spinal cord, vertebral foramen, and spinal accessory roots go through

Foramen ovale

• In between foramen spinosum and rotundum

Foramen rotundum

• Anterior to foramen ovale

• CN V2 passes through

Foramen spinosum

• Posterior to foramen ovale

• Middle meningeal a. passes through

Glossopharyngeal n.

• CN IX

• Enters jugular foramen

Hematomas - Epidural and subdural

• Epidural: Due to severed middle meningeal a.

• Subdural: Due to severed cerebral v.

Hypoglossal n.

• CN XII

• Enters hypoglossal canal

Hypophyseal (pituitary fossa)

• Were the pituitary gland sits (at the bottom of sella turcica)

Inferior sagittal sinus

• Inferior sagittal → Straight → Confluence of sinuses → Transverse → Sigmoid → IJV

Infundibulum

• Pituitary stalk

Inferior petrosal sinus

• Inferior petrosal sinus → IJV

Internal auditory meatus

• In petrous portion of temproal bone where CN VII and VIII pass through

Internal carotid a.

• Enter cranium via carotid canal

Jugular foramen

• CN IX, X, XI and IJV pass through

Middle cranial fossa

Middle meningeal a.

• ECA → Maxillary a. → Middle meningeal a. → Foramen spinosum

Occipital sinus

• Foramen magnum → Confluence of sinuses

Oculomotor n.

• CN III

• Enter orbit via superior orbital fissure

Olfactory bulbs and tract

• Sits on top of cribiform plate

Ophthalmic a.

• Branch of ICA that then enters the optic canal

Ophthalmic, maxillary, and mandibular division of CN V

• Exit via superior orbital fissure, foramen rotundum, and foramen ovale respectively

Optic n. and chiasm

• CN II

Optic foramina

• Cranial opening of optic canal

Pituitary gland

• Sits within pituitary fossa

Posterior cranial fossa

Sagittal suture

• Separates L and R parietal bones

Sigmoid sinus and sulcus

• Sigmoid sinus → IJV

Spinal accessory n.

• Roots seen exiting foramen magnum → Jugualr foramen

Spinal root

Straight sinus

• Joins confluence of sinuses

Superior orbital fissure

• CN III, IV, V1, and VI + superior ophthalmic v. pass through to get to orbit

Superior petrosal sinus

• Superior petrosal → Sigmoid → IJV

Superior sagittal sinus and sulcus

• Superior sagittal → Confluence of sinuses → Transverse → Sigmoid → IJV

Tentorium cerebelli

• Dura that separates cerebellum from cerebra

Transverse sinus and sulcus

Trigeminal n. and ganglion

• CN V

Trochlear n.

• CN IV

Vagus n.

• CN X

Vertebral a.

Vestibulochoclear n.

• CN VIII