1. Microsurgical Anatomy:3rd Ventricle

2. Introduction: The cerebral ventricular system is composed by :
the 2 lateral ventricles,
the 3rd ventricle &
the 4th ventricle.
Each lateral ventricle communicates with the 3rd ventricle through the foramen of Monro.
The 3rd ventricle communicates with the 4th through the Sylvian acqueduct

3. Introduction: Approaches are Difficult: Deeply located,
Surrounded by nervous tissue
Their curved shape
Wide variety in size among individuals
The tiny foramen through which they connect with each other are prone to obstruction

4. Vascular Relations:
The lateral ventricles & the 3rd ventricle are in close relationship with a complex arterial
irrigation system & particularly with a deep venous system draining through the complex
Galenic system
In this picture we can see that the transition from the lateral ventricle to the third ventricle contains both internal cerebral veins.

5. Approach:
The ventricular system relationship with the surrounding nervous structures will determinate the capacity to approach the cerebral lesions as well as to explain neurological deficits produced by excessive dilation in hydrocephalus or by primary growing masses or by secondary invasion.
CC: Corpus callosum; CH: Chiasma; CN: caudate nucleus; F: fornix; M: midbrain; T: Thalamus

6. 3rd Ventricle

7. Roof: lateral to 3rd ventricle transition
 from anterior to posterior : the foramen of Monoro (FM) , medially limited by the fornix columns (FC), at the ventricular body level we can see the choroid plexus (ChP)  with the superior choroid vein (CV) , laterally to the choroid plexus we have the thalamus (T). From the posterior part of the foramen of Monro we can see the septal vein medially & the thalamostriate (TSV) vein laterally.

8. Remember that  the choroid fissure between the thalamus & the fornix is forming  the medial part of the lateral ventricle floor & also the roof  of the third ventricle . This is transition region between both ventricle & is composed of 4 layers: -Neural : Fornix (f) -Tela choroidea (TC) -the internal cerebral vein (ICV) -& again the Tela choroidea.

10. Pushing laterally the choroid plexus we can see : The choroid fissure between the body of the fornix (BF) and the thalamus (T) Way at the bottom we can guess the tela choroidea.

11. If we push aside medially the fornix , we can see the internal cerebral vein (ICV) on the same side, from which arise the septal vein & the thalamostriate vein (TSV).

12. In this picture we can see both of the internal cerebral veins (ICV) on the roof of the third vetricle.

13. Here we can see, after the removal of the splenium & retraction of the crus of the fornix ,  the entry of the internal cerebral veins (ICV) into the Galenic vein (GV) at the pineal region

14. Lateral Wall:
Is formed by the hypothalamus (H) inferiorly & the thalamus (T) superiorly . They are separated by the hypothalamic groove, which is a depression that runs from the foramen of Monro to the Sylvian aqueduct (SA) passing below interthalamic mass (IM). In a saggital cut at the hypothalamic level two recesses are exposed : The optic recess (OR) upward  & the infundibular recess(IR) below. At the superior thalamic  limit , we can see  the thalamic stria mediullaris (SMT) that goes from the Habenula (Hb) to the foramen of Monoro, & this is the  fixing line of the tela choroidea  inferior of the velum interpositum. The interthalamic mass are association  fibers that connect both thalamus & is present in 75% of the population.

15. From the top to the bottom :
The foramen of Monro is surrounded laterally by the columns of the fornix (FC) that will follow a trajectory towards the mammilary bodies (MB). The anterior commisure (AC) are association fibers  located in front of the columns of the fornix. The lamina terminalis (LT) which is a thin layer of pia matter and gray matter that goes from the rostrum (RC) of the corpus callosum to the optic chiasma (Ch) in front of the anterior commissure. The lamina terminalis (LT) is visible in an anterior view unlike the fornix & the foramen of Monro. Finally the optic recess (OR) that projects to the optic chiasma.

16. Floor Wall:
From anterior to posterior : The optic chiasma (Ch) , The infundibulum (I), the tuber cinereum (TC) , the mammillary bodies , the posterior perforated substance (PPS) , the medial pairs of the cerebral peduncles (CP). As we can see , the optic chiasma & the optic tracts are used as the lateral limit of the third ventricle floor.

17. In this saggital cut we differentiate two halves: the anterior diencephalic half & the posterior  mesencephalic half.

18. Endoscopic View
from anterior to posterior,
the optic recess(OR),
The infundibular recess(IR) ,
the tuber cinereum (CT),
the mammillary bodies (MB).

19. Posterior View:
 from the top to the bottom: The habenular commissure (Hb) are formed by fibers that connect both habenular nucleus on both side of the mid line. The habenular nuclei receive afferent input from the hypocampus and amygdalian nuclei through the thalamic stria medullaris (SMT). The pineal gland (P): a backwards projection with the vision of the pineal recess (PR) The posterior commissure (PC):  just on top of the the Sylvian aqueduct (SA) carrying oculomotor reflex related fibers. The Sylvian aqueduct (SA).

20. Superior view of the posterior part of the 3rd ventricle floor
A callosotomy of the body & the splenium has been performed. The velum interpositum has been breached & then we separate both of the internal cerebral veins (ICV). We see the Sylvian aqueduct (SA) below the posterior commissure (PC). We have a clear look at the pineal Gland (P) . The habenular commissure has also been seccionated.

21. Subependymal Veins of Brain:

22. Anterior Comissure
It is a pale opallial commissure that belongs to the telencephalon.
It constitutes an essential landmark for stereotactic/functional neurosurgery.
Its ventral fibers interconnect olfactive structures, & its dorsal fibers interconnect both temporal lobes

23. Clinical Application: Ac- PC line
It is an essential landmark for localization of neuroanatomical targets in the basal ganglia & diencephalon (to treat Parkinson disease) & for relating them to stereotactic atlases.
The length of this line averages 27.07mm.
T1-&T2-weighted MR image acquisition allows minimization of geometric distortion of the magnetic fields & registration error.
Thus, the mean total difference between points on MR & CTimages is 2.2mm with a standard deviation of only1.1mm

24. AC- MB Line:
Baulacet al proposed new MRI sections of the brain in the coronal plane through a line joining the AC & the mammillary bodies displaying the constituent parts of the basal forebrain such as the septal nuclei,the preoptic area of the anterior hypothalamus,the innominate substance, & the nucleus accumbens

25. Role in traumatic Brain Injury
Because of this central position on the midline,AC atrophy (related to wallerian degeneration) can be found after severe TBI or hypoxic stress.Thus, the mean AC cross sectional volume appears significantly smaller in the TBI group compared with an age-& sex-matched cohort of typically developing children.

26. AC Absence
Some authors have reported cases of AC absence without callosal agenes is included in a unilateral pan hemispheric malformation (with ependymal heterotopia & gyral abnormalities).
Refractory seizure is the most common symptom.
Nevertheless, MRI in all cases showed the posterior limb
Genetic mutation present

27. In patients with intractable seizures,corpus callosotomy can be proposed.The persistence of postoperative seizure activity spreads interhemispherically via the remaining commissures (such as the AC, PC, & massa intermedia of thalamus). Therefore,corpus callosotomy must be total without leaving the AC intact.

28. Temporal limb of AC
The myelinated fascicles of the temporal limb of the AC serve as a substrate for neoplastic cells to invade adjacent territories, helping to explain the increasing phenomen of gliomatosis cerebri & multicentricity.