Neurosurgery notes/Anatomy/CSF anatomy/3rd ventricle

3rd ventricle

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CSF anatomy

General

  • The third ventricle is a narrow, funnel-shaped, unilocular, midline cavity.
  • It is intimately related to the circle of Willis and its branches and the great vein of Galen and its tributaries.
  • The third ventricle sits in the center of the cranium
    • below the corpus callosum, body of the lateral ventricles, and septum pellucidum,
    • above the midbrain and interpeduncular fossa,
    • anterior to the quadrigeminal cistern and vein of Galen, and
    • posterior to the anterior cerebral arteries.
  • Surgical approaches
    • The interhemispheric fissure, along the side of the falx, offers one avenue to the third ventricle.
    • The posterior part of the third ventricle can also be approached along the junction of the falx and tentorium, adjacent the straight sinus
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  • The septum pellucidum separates the bodies and frontal horns of the lateral ventricles and is crossed by anterior and posterior septal veins.
  • Vascular relations
    • Anterior cerebral artery ascends along the front wall of the third ventricle
    • Basilar bifurcation is positioned below the floor
    • Vein of Galen blocks access to the posterior wall
rp. Call.—r :or. tåonro assaA t. sept. V. Body Fomi fit. Cer. Comm.
Enlarged view.
  • The anterior wall of the third ventricle is formed by the lamina terminalis and anterior commissure and blends above into the rostrum of the corpus callosum.
  • The roof is formed by the body of the fornix and the velum interpositum through which the internal cerebral veins and medial posterior choroidal arteries course.
    • Velum interpositum
      • Is the space within the roof of the third ventricle along which the internal cerebral veins and medial posterior choroidal arteries pass.
      • The body of the fornix is located above the velum interpositum.
      • The upper wall of the velum interpositum is formed by the layer of tela choroidea attached to the lower margin of the fornix. The floor is formed by the layer of tela attached along the striae medullaris thalami. The internal cerebral veins and medial posterior choroidal arteries course between the two layers of tela. The choroid plexus in the roof of the third ventricle arises in the lower layer of tela.
  • The posterior wall, formed by the pineal and habenular and posterior commissures, is located anterior to the quadrigeminal cistern and the venous complex created by numerous veins converging on the vein of Galen.
  • The floor is formed, from anterior to posterior, by the optic chiasm, tuber cinereum above the pituitary stalk, mamillary bodies, and upper midbrain.
  • The section extends to the lateral side of the mamillary bodies.
EO Monro -„Lam. Term. hiasm. ec• Chia4b Bod Fornix Inr,: . lex. str. hal. —Pineal queduct
Enlarged view of the third ventricle.
  • This section extends just to the left of the midline through the column and body of the fornix.
  • The body of the fornix forms the roof of the third ventricle.
  • The columns pass anterior to the foramen of Monro and descend behind the anterior commissure to reach the mamillary bodies.
 
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Another third ventricle.
  • The anterior wall is made up of the lamina terminalis and the anterior commissure.
  • The optic chiasm, mamillary bodies, and midbrain are in the floor.
ro Ma Mam. Body Fomix t. Cer. V. d. Thal. .-coll. qu
Enlarged view.
  • The chiasmatic recess is located above the optic chiasm and behind the lamina terminalis.
  • The infundibular recess is located below and behind the optic chiasm.
  • The lamina terminalis blends into the rostrum of the corpus callosum.
  • The anterior commissure is positioned between the rostrum of the corpus callosum and the columns of the fornix.
  • The thalamus and hypothalamus form the lateral wall of the third ventricle
mm. amJerm. asm— it? Stalk Massa Int; Chiasm. Rec. nfundib. Rec. Mam. Body
Enlarged view.
  • The posterior wall of the third ventricle is formed by the aqueduct, pineal, and habenular and posterior commissures.
  • The pineal recess extends into the base of the pineal in the interval between the habenular and posterior commissures.
Int. Cer. V. Str. Med. Thal,:. Hab. Comm. Pineal Rec. Post. Comm.— Sup. Coll. Aqueduct Splenium Pineal
Enlarged view of the posterior part of the third ventricle.
  • The body of the fornix forms the roof of the third ventricle.
  • The velum interpositum, through which the internal cerebral veins course, is located between the body of the fornix and the striae medullaris thalami.
  • The quadrigeminal cistern and pineal region are located anteromedial to the crus of the fornix, and
  • the ambient cistern and posterior cerebral artery are located medial to the temporal horn and the fimbria.
  • Opening the choroidal fissure adjacent to the body of the fornix exposes the third ventricle.
  • The medial posterior choroidal arteries turn forward beside the pineal to reach the velum interpositum
Cau ody Lat. Ve iss ucl. Col Pine Comm. Ma CN Il . —Crus od Fimb
Lateral view of the third ventricle with the hippocampus and fornix preserved.

3rd ventricle borders

Corp.Call. Sept. Fornix F. B,åonro Ant. Cornm. Hypothal. Sulc. Lam. Ter. O. Recess o.Ch ON Infund. Recess Infund. Pit. Gland Tuber Cin. Massa Inter Thalamus Tela Hippo Comm. Hab. Comm. Suprapineal Recess Pineal Recess post. Comm. Aqueduct post. Perf. Subst Midbrain Mam. B. — Hypothal. Ill

The floor (blue)

  • Extends from the optic chiasm ↔ aqueduct of sylvius
  • Formed by
    • Anterior half: diencephalic structures
    • Posterior half: mesencephalic structures.
  • Includes the (from anterior to posterior)
    • Lower surface of the optic chiasm
      • Optic chiasm is at the junction of the floor and the anterior wall of the third ventricle.
        • Inferior surface of the chiasm forms the anterior part of the floor,
        • Superior surface forms the lower part of the anterior wall
    • Structures located between the optic chiasm and cerebral peduncles
      • Infundibulum
        • A hollow, funnel shaped structure located between the optic chiasm and the tuber cinereum
      • Pituitary gland
      • Infundibular recess
          • A diagram of the internal organs AI-generated content may be incorrect.
      • Tuber cinereum
        • A prominent mass of hypothalamic gray matter
        • Located anterior to the mamillary bodies.
        • The tuber cinereum merges anteriorly into the infundibulum.
        • The tuber cinereum around the base of the infundibulum is raised to form a prominence called the median eminence
      • Mamillary bodies
        • Round prominences posterior to the tuber cinereum.
      • Posterior perforated substance
        • A depressed, punctuated area of gray matter
        • Located in the interval between the mamillary bodies anteriorly and the medial surface of the cerebral peduncles posteriorly
    • Part of the tegmentum of the midbrain anterior to the aqueduct.

Anterior view of the floor and lower part of the third ventricle

Abbreviations:
  • A., artery; Car., carotid; Chor., choroid; CN, cranial nerve; Comm., commissure; Infund., infundibular; Mam., mamillary; Parahippo., parahippocampal; Ped., peduncle; Plex., plexus; Post., posterior; Rec., recess; Tent., tentorial.
  • The right thalamus has been removed.
  • The posterior part of the floor of the third ventricle is formed by the upper surface of the midbrain located behind the mamillary bodies.
  • The tentorial edges join at the tentorial apex located in the quadrigeminal cistern behind the aqueduct.
  • The choroidal fissure in the body of the ventricle is located between the body of the fornix and the upper surface of the thalamus.
  • The floor between the optic chiasm and mamillary bodies is located above the chiasmatic cistern.
  • The most common site for a third ventriculostomy is located just in front of the mamillary bodies.
Chor.+lex.. Tent. Edge Pa Uncus 111 Car. A. PO. Gyrus Ped. choiFi Body Fomix Thalamus Midbrai Mam. Bod
  • The anterior part of the left thalamus has been removed to expose the cerebral peduncles and upper midbrain on both sides of the third ventricle.
  • The oculomotor nerves arise below the posterior part of the floor of the third ventricle.
  • The infundibular recess is located behind the optic chiasm.
  • The pons is exposed below the mamillary bodies and infundibular recess.
Tent. rain Mam. Body• CN Ill Body Fornix —Thalam Post. Com Aquedu d. Re
  • Both thalami have been removed.
  • The third ventricular floor extends from the optic chiasm to the aqueduct.
  • The choroidal fissure in the body of the lateral ventricle is located between the body of the fornix and the thalamus, in the atrium it is between the crus of the fornix and the pulvinar, and in the temporal horn it is between the fimbria and lower surface of the thalamus.
Bulb Calcar AVIS Body 'Crus Forni ix ost. Comm Fimbria ent Ed i brai ped. Uncus — CN 111 Car. Car. A. N 11
  • Enlarged view.
  • The upper midbrain and pons are located below the floor of the third ventricle.
  • The oculomotor nerves exit the midbrain below the floor.
  • The aqueduct and posterior commissure are positioned in the posterior wall of the third ventricle in front of the tentorial apex and quadrigeminal cistern
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Anterior wall (red)

  • Extends from the optic chiasm ↔ foramen of Monro
  • From inner surface: (Inferior to superior)
    • Includes the
      • Upper surface of the optic chiasm
      • Optic recess
      • Lamina terminalis
        • The lamina terminalis fills the interval between the anterior commissure and the optic chiasm.
        • The lamina attaches to the midportion of the superior surface of the chiasm,
          • Leaving a small cleft between the upper half of the chiasm and the lamina, called the optic recess.
      • Anterior commissure
        • A compact bundle of fibers that crosses the midline in front of the columns of the fornix.
        • AP diameter of the anterior commissure varies from 1.5 to 6.0 mm.
        • The distance
          • Posterior end of anterior commissure --- Anterior border of foramen of Monro: 2.2 mm
          • Upper edge of optic chiasm --- Anterior border of anterior commissure: 10 mm
      • Foramen of Monro
        • Foramen of Monro on each side is located at the junction of the roof and the anterior wall.
        • A ductlike canal that opens between the fornix and the thalamus into the lateral ventricle
        • Extends inferiorly below the fornix into the third ventricle as a single channel.
        • Borders of the foramen of Monro
          • Anteriorly by the junction of the body and the columns of the fornix
          • Posteriorly by the anterior pole of the thalamus.
        • The size and shape of the foramina of Monro depend on the size of the ventricles:
          • If the ventricles are small, each foramen is a crescent-shaped opening bounded anteriorly by the concave curve of the fornix and posteriorly by the convex anterior tubercle of the thalamus.
          • If the ventricles are large, the foramen on each side becomes rounder.
        • Structures that pass through the foramen are
          • Choroid plexus
          • Artery: Distal branches of the medial posterior choroidal arteries
          • Veins: thalamostriate, superior choroidal, and septal veins
      • Columns of the fornix
        • The columns of the fornix form distinct prominences in the lateral walls of the third ventricle just below the foramina of Monro, but inferiorly they sink below the surface.
  • From the outer surface
    • Lower 2/3 of the anterior surface is seen on the external surface of the brain;
      • Formed by
        • Optic chiasm
        • Lamina terminalis
          • A thin sheet of gray matter and pia mater that attaches to the upper surface of the chiasm and stretches upward to fill the interval between the optic chiasm and the rostrum of the corpus callosum.
    • Upper 1/3 is hidden posterior to the rostrum of the corpus callosum.

Roof (green)

  • Forms a gentle upward arch
  • Choroidal fissure is located in the lateral margin of the roof.
  • Extends from the foramen of Monro ↔ suprapineal recess
  • Layers of the roof of the 3rd ventricle four layers:
      1. One neural layer formed by
          • Anteriorly: the fornix
          • Posteriorly: Crura and hippocampal commissure
      1. Thin superficial membranous layers of tela choroidea
          • Consists of two thin, semiopaque membranes
          • Derived from the pia mater
          • Interconnected by loosely organized trabeculae
      1. Layer of blood vessels between the sheets of tela choroidea (The space between the layers of the layers of the tela choroidea is called the Velum interpositum)
          • Internal cerebral vein and
          • Medial posterior choroidal artery.
      1. Thin Deeper membranous layers of tela choroidea,
  • Structures above the roof
    • Hippocampal commissure
    • Corpus callosum
    • Septum pellucidum
      • Attached to the upper surface of the body of the fornix
  • The velum interpositum
    • Is the space between the two layers of tela choroidea in the roof of the third ventricle
    • It is located on the medial side of the body portion of the choroidal fissure in the roof of the third ventricle below the body of the fornix and between the superomedial surfaces of the thalami
    • The upper layer of the tela choroidea is attached to the
      • Lower surface of the fornix and
      • Hippocampal commissure.
    • The lower wall has an
      • Anterior part:
        • That is attached to the small ridges on the free edge of the fiber tracts, called the striae medullaris thalami,
          • That extend along the superomedial border of the thalamus from the foramen of Monro to the habenular commissure.
      • Posterior part:
        • Attached to the superior surface of the pineal body.
          • The suprapineal recess of the third ventricle is located between the lower layer of tela choroidea and the upper surface of the pineal body.
    • The paired parallel strands of choroid plexus in the roof of the third ventricle are attached to the lower layer of tela choroidea.
      • Many of the veins draining the frontal horn and body converge on the velum interpositum to form the internal cerebral veins.
        • The internal cerebral veins arise in the anterior part of the velum interpositum, just behind the foramen of Monro, and they exit the velum interpositum above the pineal body to enter the quadrigeminal cistern and join the great vein.
        • The velum interpositum is usually a closed space that tapers to a narrow apex just behind the foramen of Monro, but it may infrequently have an opening situated between the splenium and pineal body that communicates with the quadrigeminal cistern to form the cisterna velum interpositum.
        • There also may be a space above the velum interpositum between the hippocampal commissure and splenium called the cavum vergae.

Roof of the third ventricle. Superior views

  • The choroid plexus is attached along the choroidal fissure located between the body of the fornix and the thalamus.
  • The superior choroidal veins course along the choroid plexus.
  • The thalamostriate veins pass through the posterior margins of the foramen of Monro.
  • The columns of the fornix pass anterior and superior to the foramen of Monro.
  • The body of the fornix forms the upper part of the roof of the third ventricle.
Col. Fornix For, Monro Thai. str. V. sup. Ch. V. flor. p Bod FOTO x —Th amus Chor. PI triu
The upper part of the hemispheres has been removed to expose the frontal horn and body of the lateral ventricle.
  • The right lateral edge of the fornix has been removed to expose the upper layer of tela choroidea that spans the interval below the body of the fornix and forms the upper wall of the velum interpositum in the roof of the third ventricle.
  • The velum is positioned between
    • An upper layer of tela attached to the lower surface of the body of the fornix
    • A lower layer of tela attached below the internal cerebral veins to the striae medullaris thalami.
  • The internal cerebral veins and medial posterior choroidal arteries course in the velum interpositum.
Thal.Str. V Thalamus Chor. In Bod For r. Plex ela
  • The upper layer of tela that rests against the lower surface of the body of the fornix has been preserved.
  • The tela is a thin, arachnoid-like membrane, through which the internal cerebral veins and the medial posterior choroidal arteries can be seen.
  • The anterior septal veins pass above the foramen of Monro.
Col. Thal. Str. nix For. M -Thalamus Chor. Plev Int. Cer.
The body of the fornix has been folded backward.
  • The internal cerebral veins have been retracted laterally.
  • The anterior septal veins course along the septum and join the internal cerebral veins near the foramen of Monro.
nt. Sept. y Int. ceé, v. Thalamus Tela A up. Ch. V. Cho Plex. B "Fornix
The upper layer of tela has been removed to expose the internal cerebral veins and medial posterior choroidal arteries.
  • The tela has been opened to expose the massa intermedia, mamillary bodies, and posterior commissure.
Close-up of a human body anatomy AI-generated content may be incorrect.
  • The aqueduct is positioned below the posterior and habenular commissures.
  • The pineal recess extends posteriorly between the habenular and posterior commissures into the base of the pineal
Thal.str. Massa Int Chor. A duct p ..Comm. Ha', Comm. ineal or. Monr • -;-ßhor. Plex. Pi al R Body Fornix
The exposure has been directed to the posterior part of the third ventricle.

Posterior wall

  • Extends from the suprapineal recess ↔ Aqueduct
  • Inner surface view: includes the (superior to inferior)
    • Suprapineal recess
      • Projects posteriorly between the
        • Upper surface of the pineal gland
        • Lower layer of tela choroidea in the roof.
    • Habenular commissure,
      • Interconnects the habenulae, crosses the midline in the upper lamina, and the posterior commissure crosses in the lower lamina.
    • Pineal gland,
      • Extends posteriorly into the quadrigeminal cistern from its stalk.
      • The stalk of the pineal gland has an upper and a lower lamina.
      • From the outside it is concealed by
        • The splenium of the corpus callosum above,
        • The thalamus laterally,
        • The quadrigeminal plate and the vermis of the cerebellum inferiorly.
    • Pineal recess,
      • The pineal recess projects posteriorly into the pineal body between the two laminae.
    • Posterior commissure.
    • Aqueduct of sylvius.
      • The shape of the orifice of the aqueduct of sylvius is triangular;
      • Borders of the aqueduct
        • The base of the triangle is on the posterior commissure
        • Other two limbs are formed by the central gray matter of the midbrain.
  • Outer surface view (Viewed from posteriorly)
    • The only structure visible is the pineal body.

Lateral Wall

  • Not visible on the external surface of the brain,
    • Hidden between the cerebral hemispheres
  • The lateral walls have an outline like the lateral silhouette of a bird’s head with an open beak.
      • The head is formed by the oval medial surface of the thalamus;
      • The open beak, which projects anteriorly and inferiorly, is represented by the recesses in the hypothalamus:
        • The pointed upper beak is formed by the optic recess
        • The lower beak is formed by the infundibular recess
      notion image
  • Formed by
    • Hypothalamus inferiorly
    • Thalamus superiorly.
      • Striae medullaris thalami
        • A narrow, raised ridges
        • At the superior limit of the thalamic surfaces of the third ventricle
        • These striae extend forward from the habenulae along the superomedial surface of the thalamus near the attachment of the lower layer of the tela choroidea.
    • Hypothalamic sulcus
      • Separates the hypothalamic and thalamic surfaces of the 3rd ventricle
      • A groove that is often ill-defined and extends from the foramen of Monro to the aqueduct of sylvius.
    • Habenulae
      • Small eminences on the dorsomedial surfaces of the thalamus just in front of the pineal gland.
      • The habenulae are connected across the midline in the rostral stalk of the pineal gland by the habenular commissure.
  • Massa intermedia projects into the upper half of the third ventricle and often connects the opposing surfaces of the thalamus.
    • Present in approximately 75% of brains
    • Located 3.9 mm posterior to the foramen of Monro.

Step wise dissection from floor to roof of the third ventricle

The floor of the third ventricle is located medial to the uncus and anterior perforated substance and above the midbrain.
  • From anterior to posterior, the floor includes the
    • Lower margin of the optic chiasm,
    • Pituitary stalk surrounded by the tuber cinereum, mamillary bodies,
    • Midbrain.
  • The interpeduncular fossa is located below the posterior part of the floor.
  • The anterior part of the optic tract extends along the lateral margin of the floor,
    • But further posteriorly, the tracts deviate laterally away from the floor to pass around the upper margin of the cerebral peduncle.
eyrus Rectus — c Pit stalk pptic Tr. Uncus— Aqued iiasm —Ant. peri Tuber. Ci CN am. Bod —Ci—lnterped. Fos Midbrain Lat. n. Bod
Enlarged view.
  • The tuber cinereum is situated around the pituitary stalk.
  • The infundibular recess extends into the base of the stalk.
  • A third ventriculostomy is commonly performed by opening through the thin area (yellow arrow) in the floor just in front of the mamillary bodies.
  • The oculomotor nerves arise behind the mamillary bodies below the posterior part of the floor of the third ventricle.
it. Stalk N Ill, %am. Bod Post. Perf. Subst. u t*rCin
Another specimen showing the thin area in front of the mamillary bodies (yellow arrow) through which a third ventriculostomy is completed.
  • The anterior perforated substance and optic tracts are positioned lateral to the anterior part of the floor of the third ventricle.
  • The mamillary bodies and upper midbrain are positioned below the posterior part of the floor.
'Optic Tr.— Mam. Body Aquedu
View of another third ventricle from below with the vascular structure preserved.
  • The internal carotid, posterior communicating, anterior choroidal, and posterior cerebral arteries all give rise to branches that reach the walls of the lateral and third ventricles.
  • The thalamoperforating branches of the posterior cerebral artery supply some of the posterior part of the floor of the third ventricle
 
Chiasm Pi . stałk p.Co .Ch.A. Aquduc V. Cale
Inferior view with the floor of the third ventricle removed to expose the roof.
  • The pituitary stalk has been reflected forward to expose the ventricular side of the infundibular recess and lamina terminalis.
  • The lamina terminalis slopes upward from the upper edge of the chiasm to the area in front of the anterior commissure where it blends into the rostrum of the corpus callosum.
  • The columns of the fornix cross above and anterior to the foramen of Monro and descend toward the mamillary bodies.
  • The massa intermedia crosses the midportion of the third ventricle.
  • The velum interpositum, in which the internal cerebral veins and medial posterior choroidal arteries course, is positioned between the thalami in the roof of the third ventricle.
  • The posterior commissure is exposed below the pineal gland. The vein of Galen, into which the basal veins empty, is located just behind the third ventricle.
N 11 ndib. R mm. co nro In pasa al bulvin . Of Galen).
Enlarged view.
  • The infundibular recess is located below the optic chiasm in the base of the pituitary stalk, and the chiasmatic recess is located above the optic chiasm.
  • The lamina terminalis forms the anterior wall of the chiasmatic recess.
  • The anterior commissure crosses the anterior wall in front of the columns of the fornix.
  • The foramina of Monro open upward into both lateral ventricles.
  • The lower wall of the velum interpositum is formed by the layer of tela choroidea, in which the choroid plexus in the roof of the third ventricle arises, and which is attached laterally to the striae medullaris thalami.
  • The internal cerebral veins can be seen through the layer of tela forming the lower wall of the velum interpositum.
A close-up of a human body AI-generated content may be incorrect.
Another specimen with the floor of the third ventricle removed.
  • The posterior cerebral arteries, from which the lateral and medial posterior choroidal arteries arise, passes around the midbrain.
  • The lamina terminalis is exposed above the optic chiasm and slopes upward toward the anterior commissure.
  • The columns of the fornix pass along the anterior and superior margins of the foramen of Monro and behind the anterior commissure.
  • The lower layer of tela choroidea in the velum interpositum has been removed to expose the vascular layer in the roof of the third ventricle formed by the internal cerebral veins and medial posterior choroidal arteries.
    • Another layer of tela, which spans the interval above the internal cerebral veins and below the body of the fornix, separates the vascular layer from the body of the fornix.
Car Chiasm Lam. Term. Comm. For. Monro rTe1a .Ch P,c.m_. Int. Cer. alc
Enlarged view.
  • The upper layer of tela choroidea that spans the interval below the body of the fornix has been removed. The body of the fornix, exposed by removing the upper layer of tela, blends anteriorly into the columns of the fornix that pass along the anterior and superior margin of the foramen of Monro. The lamina terminalis has been opened in the interval between the optic chiasm and anterior commissure to expose the perforating branches of the anterior cerebral artery.
Close-up of a human body anatomy AI-generated content may be incorrect.

Clinical significance

  • Tumors in the region of the third ventricle are among the most difficult to expose and remove.
  • Manipulation of the walls of the third ventricle may cause
    • Hypothalamic dysfunction:
      • Consciousness
      • Temperature control
      • Respiration
      • Hypophyseal secretion
    • Optic chiasm and tracts
      • Visual loss due to damage of the
    • Forniceal column injury (wall of 3rd ventricle)
      • Memory loss