With certain conditions a patient may develop a cerebrospinal fluid (CSF) fistula, with leakage of a clear fluid from the ears (otorrhea) or nose (rhinorrhea). Such drainage may occur years after a causative injury and may be difficult to distinguish from other fluid discharges occurring in these sites. It is important to identify these patients due to the risk of intracranial infection.
Causes of CSF drainage
(1) trauma or surgery
(2) hydrocephalus
(3) tumor
(4) congenital anomalies
(5) osteomyelitis with bone erosion
beta-2 Transferrin
Synonyms: tau transferrin, transferrin isoforms
Beta-2 transferrin (asialo-transferrin) is formed by the desialation of transferrin by neuroaminidase, which may occur in the inner ear, central nervous system or ocular humor. It is normally absent in serum, nasal secretions, tears, lymph, middle ear fluid, sputum, saliva and other body fluids. In certain very rare conditions (familial olivopontocerebellar ataxia or disialotransferrin developmental deficiency) beta-2 transferrin can be found in serum.
If electropheresis with immunofixation is performed on CSF or fluids containing CSF (or ocular humor or inner ear fluid), both transferrin (beta-1 transferrin) and beta-2 transferrin can be seen.
At least 1 mL of the drainage fluid is normally needed for the analysis. Concurrent analysis of a serum sample is sometimes recommended to prevent confusion due to glycated or other transferrin variants.
This is cheaper than imaging studies, but does not localize the defect for surgical planning.
Imaging Studies
Magnetic Resonance (MR) Cisternography:
(1) involves heavily T2-weighted magnetic resonance imaging
(2) shows an enhanced CSF signal
(3) noninvasive
(4) more sensitive (about 90%) than CT cisternography, especially in detecting small lesions
(5) specificity is only about 60% in one study (El Gammal, 1998)
High resolution CT:
(1) noninvasive
(2) showed an accuracy of 93% in one study, with an accuracy of 96% when combined with MR cisternography (Shetty, 1998)
CT Cisternography:
(1) invasive
(2) may be useful if MRI is contraindicated or if a biologically proven fistula is not seen by another technique
Intrathecal fluoresceine dye or radioisotope injection:
(1) invasive
(2) risk of infection or reaction to injected material
