Central nervous system (CNS) specimens

                  1.   CSF:  Suggested volumes are 1, 2, and 2 ml for routine, fungal, and mycobacterial cultures, respectively.

                  a.   Lumbar puncture

                        (1) Clean the puncture site with antiseptic solution and alcohol before needle insertion to prevent introduction of infection.

                        (2) Insert a needle with stylet at the L3-L4, L4-L5, or L5-S1 interspace.  When the subarachnoid space is reached, remove the stylet and spinal fluid will appear in the needle hub.

                        (3) Slowly drain the CSF into the sterile leakproof tubes.  Three tubes are generally required for microbiology, hematology, and chemistry testing.  The second tube drawn will generally go to microbiology, and the last tube drawn will generally go to hematology.  (In traumatic taps, the CSF will ofter clear as the later tubes are collected.)  Note:  Always send the most turbid tube to microbiology.

                  b.   Ommaya reservoir fluid

                        (1) Clean the Ommaya reservoir site with antiseptic solution and alcohol prior to removal of Ommaya fluid to prevent  infection.

                        (2) Remove Ommaya fluid via the Ommaya reservoir unit, and place it in a sterile tube.

                  c.   Brain abscess

                        Ninety percent of brain abscesses will grow anaerobic bacteria .  See Table 2 for anaerobic transport systems.  If an anaerobic transport system is unavailable or unsuitable for the specimen obtained, transport the specimen without delay to the microbiology laboratory for immediate processing.

                  d.   CNS biopsy samples

                        Obtain a biopsy sample from the lesion at surgery, and send it to the microbiology laboratory in an anaerobic transport system.  Do not add formalin.

 

                        Table 4  - Collection considerations for CNS specimens