The document provides a detailed anatomical overview of the third ventricle, including its structure, boundaries, the fornix's components, and surgical anatomy. It describes the roof, floor, and walls of the ventricle, as well as communication with the lateral ventricle and drainage into the aqueduct of Sylvius. Additionally, it outlines various surgical approaches to the third ventricle and the associated vascular structures.

1. Third Ventricle
Mohamed Elsayed Elsebaey
Neurosurgery Registrar
Egypt, Ismailia
Ministry of Health
Seba3y700025@gmail.com
Mohamed E Elsebaey

6. Fornix consists of 4 parts
1) Fimbria:
Fimbria hippocampi over the dentate gyrus of hippocampus. The fimbria arises in the floor of the temporal
horn on the ventricular surface of the hippocampal formation
2) Crus:
The crus wraps around the posterior surface of the pulvinar of the thalamus and arches superomedially
toward the lower surface of the splenium of the corpus callosum where it becomes related to trigon of lateral
ventricle
The two crura are connected to each other by the hipocampal commissure
At the junction of the atrium and the body of the lateral ventricle, the paired crura meet to form the body of
the fornix
3) Body:
Formed by union of the two crura below the splenium of C.C. body.
Then runs forward along the superomedial border of the thalami in the medial wall of the body of the lateral
ventricle.
The body of the fornix separates the roof of the third ventricle from the floor of the bodies of the lateral
ventricles.
At the anterior margin of the thalamus, the body of the fornix separates into two columns.
4) column:
They arch along the superior and anterior margins of the foramena of Monro in their course toward the
mamillary bodies.

7. Post
Pre

11. Recesses of 3rd ventricle are:
1) chiasmatic recess,
2) infundipular,
3) suprapineal,
4) pineal

15. •The third ventricle is a narrow, funnel-shaped, unilocular,
midline cavity.
• It has a roof, a floor, and an anterior, posterior, and two lateral
walls.

16. • Its boundaries:
• Roof: Tela choroida
•Floor: optic chiasma → infundipulum → tuber cinerium →
mamiilary bodies → posterior perforated substance →
tegmentum
• Anterior wall: superiorly by anterior commissure and cloumn
of fornix and inferiorly by lamina terminalis
• Posterior wall: Pineal body → posterior comissure →
superior colliculs → inferior colliculus
• Lateral wall: superiorly thalamus and inferiorly
hypothalamus and in between is the hypothalamic sulcus

17. Surgical Anatomy
• Communicates with the lateral ventricle
via the foramen of monro
• Drains posteriorly into the aqueduct of
sylvius
• About one 1/3 of the 3rd ventricle is
located anterior to the foramen of monro
• Extends to optic chiasm inferiorly

18. Third Ventricle

19. Walls
Anterior wall
• Consists mainly of the lamina terminalis
• Lamina terminals is thin sheet of pia and
gray matter that runs from optic chiasm
to the rostrum of the corpus callosum
• The columns of the fornix are found on
the superior lateral margins
• The anterior commissure crosses the
anterior wall at its upper end

20. Optic chiasm
Hypothalamus
Mamillary body
Tegmentum
Peduncle

21. When viewed from inferiorly, the structures forming the floor include, from
anterior to posterior,
1) the optic chiasm (anterior 3rd ventricle): The optic chiasm is located
at the junction of the floor and the anterior wall of the third ventricle. The
chiasm slopes posteriorly and superiorly from its junction with the optic
nerves. The inferior surface of the chiasm forms the anterior part of the
floor, and the superior surface forms the lower part of the anterior wall.
The optic tracts arise from the posterolateral margin of the chiasm and
course obliquely away from the floor toward the lateral margin of the
midbrain.
2) the infundibulum of the hypothalamus, the tuber cinereum,
(anterior 3rd ventricle)
3) the mamillary bodies, (Line of demarcation between anterior and
posterior 3rd ventricle)
4) the posterior perforated substance, (posterior3rd ventricle)
5) the part of the tegmentum of the midbrain located above the medial
aspect of the cerebral peduncles. (posterioir 3rd ventricle)

22. Lateral Wall
Is formed inferiorly by the hypothalamus
------------- superiorly by the thalamus
------------ posteriorly by the thalamus
Massa Intermedia:
Thalamic projection, that bridges the 3rd
ventricle at the superior posterior end

23. Floor
Starts at the optic chiasm (anterior pole)
Dips into the infundibular recess
Jumping superiorly and posteriorly over (tuber
cinereum, 2 mamillary bodies, posterior perforated
substance)
Floor of 3rd Ventricle
Cerebral
peduncle
Aqueduct of
sylvius
Anterior
Posterior

24. Floor

25. Floor, when viewed from inside endoscopically

26. Column of fornix
Anterior commissure
Lamina terminalis

27. Roof
Starts anteriorly at the foramen of monro
End posteriorly at the supra pineal recess
Is separated from the lateral wall by the
choroidal fissure
Choroidal fissure runs in the cleft between the
upper part of the thalamus and fornix

28. The Roof has four layers:
1. Fornix
2. superior tela choroidea
3. Velum Interpositum
4. Inferior tela choroidea

29. • Over ant. 1/3 of roof;
Fornices run in parallel & attached to body of fornix
• Over Post. 1/3 of roof;
The fornices are separated into forniceal crura
The roof is covered entirly by layer or white matter
called, hippocampal commissure
Also
Fornices & hippocampal commissure are covered by
loose trabecular pial tissue in the form of two
layers, called Tela Choroida

30. Between these 2 layers of tela choroida, is a
space (Velum Interpositium) through which
Internal cerebral veins &
Medial Posterior choroidal arteries , course.

31.  Tela Choroidea
Pia matter
Sup. Att. to fornix
Inf. Att. to thalamus
 Velum Interposium:
Space
Contains:
Vessels: As & Vs
Choroid plexus
CSF

32. Tela choroidea:
 The tela choroidea consists of two thin, semiopaque membranes derived
from the pia mater.
 The superior layer of the tela choroidea is attached to the fornix.
 The inferior layer of the tela choroidea is attached to the teniae thalami
and the pineal body.
Velum Interpositum:
 The velum interpositum is the space between the two layers of tela
choroidea in the roof of the third ventricle.
 The two layers of tela chooridea are interconnected by loosely organized
trabeculae and runs in between these two layers blood vessels (2 internal
cerebral veins & 2 medial posterior choroidal arteries & paired parallel
strands of choroid plexus ).
 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.

33. • Internal Cerebral Vein (ICV)
Starts at the posterior edge of the foramen of
monro, and run posteriorly to exit the velum
interpositium just above the pineal body.

34. • 3rd Ventricular choroid plexus:
Attached to the roof by tela choroida
Communicates through the choroidal fissure
with the lateral ventriclar tela choroidea

35. Posterior Wall
• Begins at the sylvius aqueduct anteriorly &
inferiorly ,
taking posterior superior direction
• Contains the posterior commissure, pineal
body, habenular commissure & suprapineal
recess above

38. Corpus callosum
Above view

39. Opening the corpus
callosum (CC)

40. Transcortical transventricular
approach
To
The Anterior part of 3rd Ventricle

41. Transcortical transventricular approach
To
Anterior part of 3rd ventricle

42. Transcallosal paraforniceal
approach

43. Intercallosal Interforniceal
approach

44. 3rd ventricle, viewed through open window in-between
the columns of fornixes
AnteriorPosterior

45. Interhemispheric
transcallosal Transchoroidal
To
Medium & Posterior Parts of
3rd Ventricle

46. Frontal Trans-Lamina Terminalis Approach
To
3rd Ventricle

47. Infratentorial supracerebellar approach
To
The 3rd Ventricle

48. Nose
3rd
ventricle
Very similar to each other in the
outline shape