BACKGROUND AND TERMINOLOGY

In 1938, Schaltenbrand used the term aliquorrhea to describe the spontaneous occurrence of an entity manifested by very low cerebrospinal fluid (CSF) opening pressures and orthostatic headaches, among other features.^1,2 Sometimes referred to as Schaltenbrand’s headaches, this later came to be known as spontaneous intracranial hypotension.³ It is now realized that practically all cases of spontaneous intracranial hypotension result from spontaneous CSF leaks,⁴ often at the level of the spine (particularly the thoracic spine⁵) and only rarely at the skull base. CSF leak leads to CSF volume depletion. Terms such as spontaneous CSF leak, CSF hypovolemia, and CSF volume depletion have been used interchangeably with spontaneous intracranial hypotension, because some patients with this disorder have consistently normal CSF opening pressures.^5,6 True hypovolemic state (reduced total body water), CSF shunt overdrainage, dural holes or tears as the result of lumbar puncture, epidural catheterization, surgery, and trauma all may lead to loss of CSF volume. In this chapter, we focus on spontaneous CSF leaks.

ETIOLOGY OF SPONTANEOUS CEREBROSPINAL FLUID LEAKS

The cause of spontaneous CSF leaks often remains undetermined, but two etiologic factors should be considered: trivial trauma and weakness of the dural sac.

Some patients report a history of trivial trauma, such as coughing, pushing, trivial falls, lifting, and sports activities. Evidence for weakness of the dural sac is accumulating. Meningeal diverticula are seen more frequently in patients with spontaneous CSF leaks. Increased frequency of meningeal diverticula and also CSF leaks have been reported in Marfan’s syndrome.^7–9 Some patients with spontaneous CSF leaks show stigmata of the disorders of a connective tissue matrix (e.g., marfanoid features, hyperflexible joints, hyperextensible skin).^5,10

In uncommon instances, a dural tear from a spondylotic spur or disc herniation^11,12 may cause dural defect and CSF leak.

CLINICAL MANIFESTATIONS

Headache is the most common manifestation. It is “classically” orthostatic (present in upright position, relieved by recumbency).^3,5 It is often not throbbing, but it may be throbbing; it is often bilateral, but it may be unilateral; and it is often aggravated or sometimes even triggered by Valsalva-type maneuvers. The headache may be frontal, fronto-occipital, holocephalic, or occipital. Not all headaches in CSF leaks are orthostatic, and variability is substantial (Table 62-1).^5,13–17 Furthermore, not all orthostatic headaches result from CSF leaks. For example, they can be the dominant clinical manifestation in some patients with postural tachycardia syndrome.¹⁸

TABLE 62-1 Headache Variations in Cerebrospinal Fluid (CSF) Leaks

MRI, magnetic resonance imaging.

CLINICAL MANIFESTATIONS OTHER THAN HEADACHES

Many of the patients with spontaneous CSF leaks have one or, often, more symptoms in addition to the headaches (Table 62-2).^3,5,19–32

TABLE 62-2 Clinical Features Other Than Headaches

Proposed mechanisms of clinical manifestations in CSF leaks and intracranial hypotension are listed in Table 62-3.^3,5,19–34

TABLE 62-3 Mechanisms of Clinical Manifestations or Cerebrospinal Fluid Volume Depletion

DIAGNOSIS

Cerebrospinal Fluid Examination

Considerable variability, not only between different patients but also in the same patient if multiple taps are performed at different times, is to be expected.

The opening pressure is typically low, sometimes unmeasurable, and sometimes it is “low normal” or even consistently within normal limits.

Analysis reveals the following characteristics:

Color: often clear, occasionally xanthochromic.

Protein concentration: normal or elevated (protein concentrations up to 100 mg/dL are common, and a concentration up to 1000 mg/dL has been reported).¹⁵

Glucose concentration: never low.

Leukocyte count: normal or elevated (pleocytosis with counts up to 50 cells/mm³ is common, and a count up to 222 cells/mm³ has been reported).⁵

Erythrocyte count: normal or elevated (difficult and traumatic taps are common in this disorder, and epidural venous plexus may be dilated).

Cytological and microbiological profiles: always negative.

Radioisotope Cisternography

Indium 111 is the radioisotope of choice. This is introduced intrathecally, typically through a lumbar puncture, and its movement is monitored by sequential scanning at various intervals, up to 24 or even 48 hours. Normally, by 24 hours (but often earlier), substantial radioactivity can be detected over the cerebral convexities. When a spinal CSF leak exists, the activity typically does not extend much beyond the basal cisterns. Therefore, images at 24 or even 48 hours reveal either absence or paucity of activity over the cerebral convexities.^35–37 This finding is the most common cisternographic abnormality in CSF leaks. Detection of parathecal activity that may point to the level or approximate site of the leak, although more desirable, is noted much less commonly (Fig. 62-1). Furthermore, meningeal diverticula, if large enough, may appear as foci of parathecal activity. Another cisternographic observation in CSF leaks is the early appearance of radioactivity in the kidneys and urinary bladder (<4 hours versus 6 to 24 hours), indicative of early entrance of extravasated isotope into the venous system and its early renal clearance and early appearance in the urinary bladder.

Figure 62-1 Indium 111 cisternography in a patient with spontaneous cerebrospinal fluid (CSF) leak. Note parathecal activity at 2 hours pointing to the level of CSF leak. At 24 hours, there is paucity of activity over the cerebral convexities, although activity can be seen in the spinal canal and, in particular, the basal cisterns.