Meningitis and subarachnoid hemorrhage are serious life-threatening
conditions. They require prompt and accurate diagnosis in the Emergency
Department due to their significant morbidity and mortality. There
are many diagnostic modalities available to the Emergency Physician
to assist in the diagnosis. However, lumbar puncture (LP) is still
considered the gold standard. Lumbar puncture is a procedure that
is often performed in the Emergency Department to obtain information
about the cerebrospinal fluid (CSF) to aid in the diagnosis
of a variety of medical conditions. Knowledge about the proper indications,
contraindications, various techniques, equipment, and recognition
and treatment of its complications is vital to any physician
that performs this procedure. A lumbar
puncture should be performed after a thorough neurological exam.
Significant morbidity and mortality can result if the procedure
is performed on the wrong patient.
While the entire cavity of the brain and spinal cord has a volume
of approximately 1650 mL, CSF occupies approximately 150 mL of this
volume. The brain literally floats in the CSF because the specific
gravity of the CSF and brain are approximately the same. Approximately
500 mL (0.35 mL/min) of CSF is produced each day. Most
(over two-thirds) of the CSF is produced by the choroid
plexus within the lateral ventricles. Small amounts of choroid plexus
can also be found in the third and fourth ventricles. Small amounts
of CSF are secreted by the ependymal surfaces of the ventricles.
A minimal volume of CSF is produced by the brain through the small perivascular
spaces that surround the blood vessels entering the brain substance.
The flow of CSF through the ventricular system is rather simple
(Figure 96-1). CSF produced in the lateral ventricles flows through
the foramina of Monro into the midline third ventricle. It then passes
through the Aqueduct of Sylvius into the fourth ventricle. From
the fourth ventricle, the CSF flows into the cisterna magna via
two lateral openings (foramina of Luschka) and one midline opening
(foramen of Magendie). The cisterna magna is located beneath the
medulla and cerebellum and is continuous with the subarachnoid space
that surrounds the brain and spinal cord. The CSF then flows through
the subarachnoid space to bathe the brain and spinal cord. The CSF is
absorbed back into the venous system by way of arachnoid villi.
CSF circulation around the brain and upper spinal cord.
CSF pressure should average 130 mmH2O when measured
in the lateral decubitus position. It can range from 70 to 180 mmH2O
in a normal person. Since the CSF production rate is constant, the
pressure is regulated by the rate of CSF absorption by the arachnoid
villi that act as one-way valves into the venous blood of the dural
sinuses. Certain disease states may impede reabsorption and lead
to increased intracranial pressure.1