Wednesday, 11 June 2008

How can you confirm a cerebrospinal fluid leak in a base of skull fracture?

Basilar skull fractures (i.e. base of skull fractures) have a high incidence of dural tears and thus a higher than average risk of meningitis - although it is controversial whether or not to give prophylactic antibiotics. The basics to know about this condition are as follows:

Firstly, skull X-rays are almost never of any help in diagnosing basilar skull fractures. You need to go by clinical signs.

Clinical signs include:
  • Raccoon eyes - this refers to a periorbital (around the eyes) bruising, and is a result of blood tracking down from the skull fracture site to the soft tissue around the eyes.

  • Battle's sign - named after a guy (unsurprisingly) called Battle, this is bruising around the mastoid process (behind the ears). As with raccoon eyes, this bruising is due to blood tracking there from the skull fracture, not from damage directly to the mastoid process.

  • Cerebrospinal fluid (CSF) otorrhoea -this is leakage of CSF out your ear, via a combination of a ruptured tympanic membrane and nearby basilar skull fracture.

  • CSF rhinorrhoea - similar to the otorrhoea story, this is leakage of CSF out your nose. Usually (but not exclusively) the ethmoid cribriform plate is the part fractured.

  • Cranial nerve palsies - many of the cranial nerves run nearby enough to be injured or compressed by a fractured base of skull.

A good question that might now arise is how you tell if fluid coming out the nose or ears is CSF - it could be pure blood, or it (in the case of nasal discharge) it could be the normal nasal secretions. There are a number of tests you can do.

Firstly, CSF should have glucose in it, whereas this is unlikely in normal nasal secretions, and so measuring the glucose (initially on dipstix, and then formally) is helpful.

Secondly, if you are dealing with a bloody fluid, you could try to look for the halo sign (or ring sign). Dab some of the blood on a tissue. If there is CSF mixed with the blood, it will move by capillary action further away from the centre than the blood will. You'll get something like this:

These tests are helpful pointers, but they aren't wholly accurate. If you want to be more sure, measure the level of beta-2-transferrin in the fluid. This protein is only found in CSF, so if you are finding it in fluid coming from the nose or ears, you have a CSF leak.

If you have any of these signs present, you may be dealing with a basilar skull fracture. To confirm your diagnosis, you need to organise a CT scan of the area. This is more or less the diagnostic procedure followed in most hospitals.

6 comments:

  1. I got a good follow-up question to this post:

    "hello doc,

    Thank you very much for the answer.
    I am not that clear with the halo sign. If blood was present, would there not also be a yellow ring? Blood would clot and appear in the center. If it is so, we will have to compare the normal blood and
    blood and csf on tissue paper. The sample with CSF would have a wider ring. Does that sound way too crazy?"

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  2. I think you're on the right track there. When blood clots, there can certainly be a separation of the solid constituents (mainly red blood cells) from the plasma. The plasma would then be capable of spreading out on the tissue/blotting paper quicker than the rest, which could cause a halo sign of sorts.

    But I think this effect:

    (1) takes time - the halo sign is usually present in the case of CSF long before the blood fully clots

    (2) is quite minimal. CSF produces a much more marked effect.

    But you nonetheless bring up a really good point that is worth emphasising again. The halo sign is NOT hugely specific or sensitive - it simply isn't a diagnosis-clincher. It's simply a sign that is an improvement on a random guess.

    Don't take my word for it though. For those interested in a little more detail, there's a nice article here about CSF rhinorrhoea. The relevant passage about the halo sign is:

    Most of us have read about the halo sign. CSF will separate from blood when the mixture is placed on filter paper resulting in a central area of blood with an outer ring or halo. Dula et al studied this ring sign and found that mixtures of CSF and blood will produce a clinically detectable ring with CSF:blood ratios of 30%-90%. Blood alone does not produce a ring. The best ring was obtained with a 50: 50 mix of blood and CSF. More importantly, they found that the presence of a ring was not exclusive for CSF. Blood mixed with tap water, saline, and rhinorrhea fluid also produced a ring. The halo sign does occur, but clearly does not clinch the diagnosis.

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  3. Thank you very much. It helps me a lot with my finals. It saves my time, reading the textbook.

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  4. excellent job...keep helping us...tnx

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  5. Thank you very much.

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