Absent headache despite CSF volume depletion (intracranial hypotension)

Report of cases.

Patient 1. A 78-year-old woman with a history of rheumatoid arthritis was seen in March 1994. She had a 3-year history of progressive unsteadiness of gait, intermittent difficulty with bladder control, and mild memory loss. She needed the help of at least one person to walk. Head MRI showed a 4 × 2.5-cm midline posterior fossa arachnoid cyst and an associated occult hydrocephalus (figure, A and B). After treatment with a right ventriculoatrial and cystoatrial shunt, her gait markedly improved. At follow-up at 14 months, an unenhanced head MRI showed the shunt tubes in place, a mild decrease in the size of the ventricular system, and thin subdural fluid collections on the right. She could now walk independently, though arthralgias impaired her gait. A contrast-enhanced head MRI in January 1996 showed diffuse pachymeningeal gadolinium enhancement and engorged sagittal sinus. Decompressed arachnoid cyst and ventricular system, and thin subdural fluid collections were present as noted previously (figure, C and D). The patient never had headaches or postural symptoms. The diffuse pachymeningeal enhancement and collections of subdural fluid were thought to be secondary to an overdraining CSF shunt. In the absence of clinical accompaniments, it was decided not to revise the shunt. A follow-up head MRI in November 1996 showed no change. She has remained headache free. FIGURE

• Download figure
• Open in new tab
• Download powerpoint

Figure. Enhanced T1-weighted coronal (A, C) and unenhanced T2-weighted axial (B, D) MRI. MRI from March 6, 1994 shows dilated ventricles and the midline posterior fossa arachnoid cyst (A, B). MRI from May 21, 1996, approximately 2 years after shunting procedure, shows decompressed ventricles and arachnoid cyst and diffuse pachymeningeal gadolinium enhancement, as well as an increase in size of the sagittal sinus, all suggesting CSF shunt overdrainage. The patient had no headaches.

Discussion.

CSF leak or CSF shunt overdrainage leads to CSF volume depletion. Because the skull and, for the most part, the spinal canal are rigid containers, in the presence of intact skull and undisturbed brain, based on Monro–Kellie doctrine, a decrease in CSF volume should cause an increase in intracranial blood volume.7 This is primarily reflected on the venous system and the meningeal veins. Because the leptomeninges have a blood–brain barrier and pachymeninges do not, in CSF volume depletion the pachymeninges enhance with gadolinium. Other volume compensatory phenomena include enlargement of the pituitary gland (related to engorgement of pituitary veins, sinuses, and portal systems), prominence of cerebral venous sinuses, and subdural collections of fluid.

Another consequence of CSF volume depletion is descent of the brain (“sinking brain” or “sagging brain”). This is often well demonstrated by MRI, but would be probably even more pronounced and more frequently documented if MRI of the head were performed with the patient upright rather than supine,4 a position in which patients are typically less symptomatic or asymptomatic. The headache of CSF volume depletion is thought to be caused by descent of the brain and resultant traction on its pain-sensitive suspending structures. The traction and distortion of these structures is produced or increased in upright posture and, therefore, the typical headaches are entirely or primarily orthostatic in character.8

The clinical and imaging syndrome resulting from CSF volume depletion shows considerable variation. Although many patients display all the classic and expected features of the syndrome, including orthostatic headaches, low CSF pressure, and pachymeningeal gadolinium enhancement, a significant minority of patients do not. In some patients, CSF pressures may be consistently within normal limits.9 In other patients, meningeal enhancement may be absent.8 Yet in another group, such as those patients reported herein, headache may be absent, and the patient may be essentially asymptomatic in relation to the CSF leak or shunt overdrainage.8,10⇓ The independent variable in all of these forms of clinical imaging is a decrease in CSF volume. The CSF pressure, the MRI abnormalities, and the clinical manifestations are dependent variables that may alter considerably.

Our first two patients never developed headaches. The third patient had an initial orthostatic headache that responded to epidural blood patch, with reduced pachymeningeal enhancement and continued CSF leak but without headaches.

When the headache is absent (such as in the cases reported here), the patient is usually though not invariably an elderly patient10 who has undergone CSF shunting (usually for a communicating hydrocephalus) and has an overdraining CSF shunt. The CSF pressure is typically low, evidence of infection or inflammation is absent on CSF analysis, and diffuse pachymeningeal gadolinium enhancement is noted on MRI. Sometimes, other related MRI abnormalities may be seen, such as subdural fluid collections. Nonetheless, evidence of sinking of the brain is typically absent. As previously hypothesized,10 it is likely that in these elderly patients with hydrocephalus, a balance may occur between the decreased CSF volume and the buoyancy of the brain with its reduced weight, that the brain may not sink substantially to produce headaches.