Examination of brain and spinal cord

Removal of the brain
Scalp is incised along the coronal plane from a point behind one ear and extended to a corresponding point behind the other ear. Underlying deep scalp tissue is peeled off by traction, freeing with the help of knife, where required. In cases with injuries present over the head, scalp must be reflected till the nape of the neck. Face is peeled upwards from jawline or downwards from forehead, to examine facial injuries. This procedure is not practiced routinely owing to restoration hassles and cosmetic flaws.

On exposure of skull vault, hand saw or electric saw is used to cut through the outer table of skull, angled downwards and backwards from forehead and downwards and forwards from the occipital area. Careful sawing is necessary to avoid artefacts mimicking head injuries. A chisel and hammer can be used to remove skullcap ensuring that the dura mater remains intact.

The skull and dura mater is examined for extra-dural and sub-dural hemorrhages before being cut circumferentially. Falx Cerebri is separated with help of blunt scissors passing at the Falx and cutting at the extreme of depth. Frontal lobes of the brain are reflected carefully, and cranial nerves, optic chiasma and pituitary stalk separated with the help of a scalpel. Each side of Tentorium Cerebri is cut along the line of petrous part of temporal bone extending to lateral wall of skull. Scalpel can be used to transect the spinal cord at a furthermost reachable point, from the foramen magnum.

By gently sliding the hand below the brain, it is rotated backwards for removing any adherent dura. Floor of the skull is now examined after stripping the dura with forceps, to reveal basal fractures, if present. Petrous part of temporal bone can be sawed to look for any hemorrhages in the middle ear.

With a chisel and hammer, dorsum sellae is fractured along its upper anterior surface. Diaphragm of the Sella can be grasped with forceps and a pair of scissors used to cut around its margins. Upward traction raises the pituitary gland from its fossa, allowing a scalpel or fine scissors to transect the inferior connections for removal.

Examination of the brain
After removal of the brain, it is weighed first. It is then up to the examiner whether to examine it immediately or following fixation. In cases of neurological significance, it is always advisable to fix the brain in formalin and dissect it several weeks later. Fixed brain becomes more firm and hence thinner sections can be made, whether for naked eye or for histopathological examination. In cases where the brain is softened due to ischemia or infarction, it is also advisable to fix the brain.

Fixation is not required in most cases, especially if the lesions are apparently visible on examination. While dissecting the wet brain if the examiner thinks the brain needs to be fixed, it is suggested to immediately stop the dissection and submerge the slices and remaining brain in formalin buffer. Subarachnoid hemorrhage if present should be recorded before setting the brain for fixation.

Wet or fixed dissection, the procedure for examination of brain remains the same. Symmetry of cerebrum and/or any contusions or herniation should be examined first by surface examination. Hippocampal herniation, flattening of gyri and filling of sulci are suggestive of cerebral edema. Cerebral tonsilar coning can be confused with anatomical pouting. Meninges should be examination to look for sub arachnoid, sub-dural or extra-dural hemorrhages. Cerebral blood vessels like circle of Willis is examined to look for any aneurysms. Fluctuant masses under the cerebral cortex should be palpated to confirm internal hemorrhages, cystic tumors and abscesses.

Initial cut is made through peduncles of cerebrum by brain knife, which separates cerebrum from cerebellum and brain stem. Cerebellum is then examined for substantia nigra and aqueduct. Cerebellum is cut vertically to display fourth ventricle and dentate. Pons and medulla are sectioned transversely. Along the coronal plane, cerebral hemispheres are cut in serial sections measuring about 1 cm each.

Removal/examination of spinal cord
Examination of spinal cord is not indicated unless injuries or anomalies exists. However, where damage to vertebral column is suspected, one should never hesitate in examining the spinal cord. Two approaches can be used to access spinal canal – anterior approach and posterior approach.

The posterior approach is more commonly used. A midline incision is made from occiput to lumbar region. Para-spinal muscles are reflected along with underlying sub-cutaneous tissue. Parallel saw cuts are made with an oscillating saw or a Rachiotomy saw, down the length of the spine, dividing right and left laminae and providing access to spinal canal. Caution must be applied not to cut deep as this may result in perforation of spinal dura. The cuts must be placed as laterally as possible, to allow cord to be removed with ease.

In anterior approach, the vertebral bodies are removed by sawing through the pedicles laterally. Heads of the ribs usually makes this procedure difficult. The only advantage is that the body need not be turned over and external disfigurement is minimal.

Once the canal is exposed by either approach, dura is examined for any anomalies or infections. Nerve roots are then detached from dural attachments and dura is carefully opened with forceps and scissors to examine the cord. It is then peeled out from the canal, caudal to cephalic. It is examined following fixation with formalin, before samples are taken for histopathology. Following removal of the cord, the canal is examined for any protrusion of disc, fracture or dislocation.

How to fix the brain in formalin?
Ten percent buffered 5 to 8 liters formalin is taken in a wide mouth container to allow the brain to be submerged completely. Brain is removed leaving falx and parasagittal bridging veins intact. The brain is then suspended from the falx, in an upright position.

Alternative method
A thread or metallic clip is used to hold basilar artery and tied across the mouth of container, leaving the vertex clear from the bottom. The weight of the brain increases by up to 8 % after fixation in formalin.