Clinical Skills Pearl Vol 2 (#14): Incidental brain findings on MRI c/o of Dr. Klimek

Why does CSF leak? (How does one measure CSF pressure?)

(Magnaes B. Body position and cerebrospinal fluid pressure. Part 2: Clinical studies on orthostatic pressure and the hydrostatic indifferent point .J. Neurosurg 1976;44:698-705)

There is conceptually a position in the body in which measured CSF pressure does not change during the transition from lateral decubitus to sitting upright.

Imagine that a person is lying down. The opening CSF pressure is the same along the entire length of the spinal canal. With tilting into a vertical posture the pressure of the column of CSF must (like a manometer tube) be proportional to the height of the column (greater at the bottom, less at the top).

In a control group of 72 normal patients, spinal taps were undertaken and the pressure measured as the patient was tilted from lying to sitting upright.

The normal lying CSF pressure measured ranged from 50 to 180 mm H2O. The CSF pressure in the sitting position ranged from 320 to 630 mm (H2O) with a mean of 490 mm. During continued sitting the CSF pressure rose 20 to 60 mm over one hour and returned to normal after lying for 5 minutes.

The occipital prominence is the palpable anatomical landmark beyond which 71 out of 72 normal patients had zero CSF pressure. In other words, maximal CSF pressure measured within 15 minutes of sitting was less than the height of the occipital prominence.

Thus, if one were to measure the opening pressure in the sitting position, it is not higher than the occipital prominence if measured before the increase pressure adaptation occurred.

Therefore a CSF leak above this level would not be accentuated by standing and walking about. However, the possibility of air entering the CSF would be a consideration.