Type:
Educational Exhibit
Keywords:
Not applicable, Education and training, Dilatation, Cerebrospinal fluid, History, Education, Complications, MR, CT-Angiography, CT, Management, Head and neck, Anatomy, Neuro
Authors:
A. N. Khan1, K. S. Babar1, U. S. Umer1, R. A. Shah2, M. Khan1, S. Shabir3, Z. Malik4, A. Jang1, M. Kumar5; 1Peshawar/PK, 2Islamabad/PK, 3Rawalpindi/PK, 4Islamabad /PK, 5Karachi/PK
DOI:
10.26044/ecr2020/C-15125
Background
In this section, we will discuss the definition and pathophysiology of spontaneous intracranial hypotension (SIH) that will assist in understanding the radiological features.
Definition:
Spontaneous intracranial hypotension is defined as a rare neurological disease presenting with postural headaches related to decrease in cerebrospinal fluid pressure, commonly due to CSF leak [1].
Intracranial hypotension can occur spontaneously or secondary to other events like trauma and intervention, but here we will discuss spontaneous cause, which is most commonly due to dural abnormality leading to CSF leakage.
Pathophysiology:
Monro-Kellie hypothesis:
In the normal adult, the skull encompasses a total volume of 1450 mL: 1300 mL of brain, 65 mL of CSF, and 110 mL of blood.
The Monroe-Kellie hypothesis states the summation of the intracranial volumes of blood, brain, CSF, and other constituents is fixed, and that a rise in any one of these must be compensated by an equal decline in another or else pressure increases and vice-a-versa [2].
Therefore, in a case of spontaneous intracranial hypotension there is CSF leakage leading to decrease in CSF volume and compensatory increase in volume of venous blood volume with relatively fixed volumes of rest of constituents and formation of subdural collections Fig. 1 .
Fig. 1: Diagrammatic presentation of Monro-Kellie hypothesis in normal state and spontaneous intracranial hypotension.
Loss of buoyant force of CSF and mechanism of orthostatic headache:
As the CSF volume has decreased, there is loss of buoyant force of CSF, which leads to sagging of the brain. This in combination with venous engorgement causes traction on veins, meninges and nerves, resulting in headaches. Sagging of brain and venous engorgement are accentuated in standing position, which explains the orthostatic pattern of headache[3].