The scope of knowledge here is not necessary required for medical school, but the relationship of the anatomical relationships of the third ventricle is required, as this will help and explain pathology.
To understand the certain types of pathology affecting the third ventricle one must appreciate the anatomical relationships.
Please make note of the following structures:
The Roof: of the third ventricle is formed by the Tela Choroidea (capillary plexus in the choroid plexus)
The floor: hypothalamus and its associated structures
The Posterior: Pineal Gland
The Anterior: Lamina Terminalis
Lateral: the thalamus forms the lateral walls of the third ventricle
The third ventricle has two indentations called the supra-optic recess and the infindibular recess.
Please note the close relationship between the Midbrain and the Pineal Gland. This will form the basis of Parinaud’s Syndrome
These are remnants of Rathke’s Cleft. There are two types those that occurr in children (adenometous type) and occurr in adults (papillary type). Adult tumours are more aggressive than children. These tumours have an epithelial lining and enlarge slowly by shedding epithelium into the cavity. They also deposit cholesterol and fat content into the tumour cavity.
Clinical Effects of the tumour
1. The most important concepts to identify is that compression of the optic chiasm from above. Therefore any lesion that compresses the optic chiasm will cause an INFERIOR BITEMPORAL HEMIANOPIA
2. If the tumour extends anteriorly it will cause compression at the frontal boundary of the 3rd ventricle leading to acute hydrocepalus
3. If the tumour extends superiorly it can block the inter-ventricular foramen leading to acute hydrocephalus, with dilation of the lateral ventricles.
4. If the tumour extends inferiorly it can compress the hypothalamus and pituitary leading to pituitary dysfunction, dwarfism, growth retardation in children and diabetes insipidus
As medical students please don’t get bogged down with the histology of a craniopharyngioma but understand the ANATOMY, this will make things a lot easier to understand
Pineal Gland Tumours
Look at the anatomy of the Pineal Gland this is important.
- Anteriorly 3rd ventricle
- Inferiorly the midbrain tegmentum and aqueduct of Sylvius.
You can almost guess what may happen as a result of a pineal gland tumour. The majority of pineal gland tumours are benign and include germinoma or teratomas. They can secrete B-HcG, Placental ALP and Alpha Feta Protein
The other tumours arise from the substance of a pineal gland tumour are called pineal gland tumours, pineoblastoma’s (extremely aggressive tumour)
Patient with pineal gland tumours can compress the midbrain causing an impairment in upward gaze. Remember the midbrain contains vertical gaze eye centres and therefore impairment.
Parinaud’s Syndrome Presents:
- Impaired upward gaze
- Pseudo Argyll-Robertson Pupils
- Convergence-Retraction Nystagmus
- Eye-lid retraction
Note impaired sun-setting sign is extremely poor sign and downward gaze in the presence of acute hydrocephalus is a medical emergency.
3rd Ventricular Colloid Cysts
Colloidal cysts can obstruct the foramen of Munro and cause significant headaches and obstructive hydrocephalus. If not suspected these patients can undergo significant raised ICP and death.
Management is conservative unless there is a diameter of >10mm or obstructive hydrocephalus.
With acute hydrocephalus these patients undergo bilateral EVD insertion to decompress the lateral ventricles.