This hypothesis states that
- The volume of 3 components in brain (tissue, ICF and blood) is nearly constant in a state of equilibrium.
- The average intracranial volume in an adult is 1700 mL = 1400 mL (brain tissue) + 150 mL (ICF) + 150 mL (blood, mainly in veins)
A decrease in the volume of one compartment is compensated by the increase in the volume of another compartment.
- Eg in idiopathic intracranial hypertension, there is slit like ventricles (decreased ICF) and smaller size of pituitary gland i.e empty fossa (decreased blood flow)
How does this apply in intracranial hypotension?
- Characteristic features in intracranial hypotension: venous distension sign, pachymeningeal enhancement, subdural effusion
- A decrease in ICF is compensaterd by increased blood volume (venous hyperemia and engorgement)
– Venous distension sign is due to venous engorgement (sinus becomes round instead of triangular)
– Pachymeningeal enhancement is due to pressure gradient induced leak in gd into the pachymeningeal layer (which
lacks blood-brain barrier unlike leptomeningeal layer)
– Subdural effusion is due to leakage from venous engorgement (like edema in lower extremities)
- Bahram Mokri, MD. The Monro-Kellie hypothesis. Applications in CSF volume depletion. Neurology 2001;56:1746-48