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Before commencing a post–mortem examination on any patient known to have had some neurological disease, the pathologist must consider – preferably in consultation with the clinician – what special steps might have to be undertaken prior to fixing the brain. If there is any clinical suspicion of meningitis, some of the exudate should be sent for bacteriological examination – micro–biologists prefer exudate itself rather than a swab; if any type of encephalitis has been considered in the differential diagnosis, representative samples of brain tissue should be placed in an appropriate transport medium and sent for virological examination – and also samples of blood and cerebrospinal fluid for serological studies; if there is a possibility of some lysosomal enzyme deficiency, e.g. one of the neuronal storage disorders, or an unusual type of demyelinating disease, some brain tissue should be deep frozen as quickly as possible in case it is required later for neurochemical analysis; and if the post–mortem examination is being undertaken soon after death, the possibility of taking samples of the brain for electron microscopy should be borne in mind.
There are two basic principles in removing the brain – all structures holding it in position must be cut without inflicting any damage on the brain, and undue stretching of the brain stem must be avoided since it is very liable to tear at the level of the midbrain (see Fig. 1.26).
Widespread sampling of peripheral nerve and muscle is essential in any patient thought to have had some type of neuromuscular disease. Many of the enzyme histochemical techniques routinely used in the examination of muscle biopsies can still be applied to muscle taken up to 24 to 36 hours after death. Thus some specimens of muscle taken post mortem should – properly labelled – be frozen in liquid nitrogen as quickly as possible. Most specimens of nerve and muscle are, however, simply fixed in neutral 10% formal saline. The selection of muscles and peripheral nerves to be examined will be determined by the clinical pattern of the disease, and prior discussion with the appropriate clinician is therefore essential. For a complete picture of peripheral neuropathy, cranial nerves, the trigeminal ganglia, posterior root ganglia and various peripheral nerves need to be examined. Once the posterior root ganglia in the lumbar and sacral region have been exposed (see Figs. 4.11 and 4.12) it is not difficult to continue the dissection distally to free all of the major nerves constituting the brachial plexus. Other nerves can be sampled individually.
This is a rather expert field, however, and before undertaking a post–mortem examination on a patient known to have some disorder of muscle or peripheral nerve it is advisable also to consult a neuropathologist. It may, for example, be important to attempt to examine the small muscles of the hand, and intramuscular nerves and end plates adjacent to the motor point in a muscle.
The type of dissection depends to a certain extent on the site of any abnormality suspected of being present. Thus if there is thought to be a midline lesion affecting the third or the fourth ventricle, a midline sagittal section may be indicated (Figs. 7.23 – 7.25) and on occasion there may be good reason for slicing the brain in the planes demonstrated by the C–T head scanner. In general, however, the method described below is the most informative since it produces the maximum amount of information about distortion of the brain, the size and shape of the ventricular system, the presence of internal herniae and the appearances of the basal nuclei and the hippocampus (Ammon's horn).
Figs. 7.1 and 7.2 The first step is to make a transverse cut through the rostral pons. The scalpel blade should be large and have a broad base (e.g. Swann-Morton No. 22).
Place the brain, superior surface downwards, on a non–slippy surface – a sheet of cork is probably the best. Insert the scalpel blade right through the lateral surface of the pons just caudal to the oculo-motor nerves (arrow). Extend the cut transversely to the other side of the pons and lift the cerebellum and the brain stem away from the cerebral hemispheres. Care must be taken not to damage the medial parts of the temporal lobes with the scalpel.
The spinal cord should be examined routinely in every post-mortem examination on a patient with a disorder of the central nervous system. This may, on occasion, appear to be an unnecessary labour but even in a patient thought to have died as a result of a severe head injury, removal of the spinal cord may disclose that there has been an unsuspected fracture/dislocation of the cervical spine; and in a patient known to have a malignant brain tumour, examination of the spinal cord may disclose that diffuse tumour or seedlings in the spinal subarachnoid space have materially contributed to the clinical picture. And there are numerous metabolic derangements including disseminated systemic malignant disease where long tract degeneration in the spinal cord, particularly in the posterior columns, has been the principal source of neurological dysfunction. If the cord is not removed precise clinico-pathological correlations can never be established in such cases.
There is inevitably a certain reluctance on the part of the pathologist and the mortuary attendant to remove the cord because of the extra time and labour involved. In cases of particular interest, the best technique is to remove the entire vertebral column so that a careful dissection can be undertaken after appropriate preliminary fixation but, using the anterior approach illustrated here, removal of the spinal cord and posterior root ganglia can with experience be accomplished in little more than 10–15 minutes.
As indicated in the preface, this chapter is not intended to be a detailed atlas of neuroanatomy. Its aim is simply to illustrate the principal anatomical structures in the brain, using photographs rather than diagrams, that should be recognised by a competent pathologist, if only to allow him to state reasonably precisely the site of any lesion identified post mortem. Provided slices of uniform thickness have been cut as described on p.104 using a very simple technique, the pathologist will also be able to measure the size of any abnormality with a reasonable degree of accuracy.
The first four illustrations demonstrate the principal structures on the medial and lateral surfaces of the brain and at the base of the brain. These are followed by a series of coronal slices of the cerebral hemi-spheres. Fig. 8.11 includes the mamillary bodies and represents the first cut made in the cerebral hemispheres as suggested on p.100. Thus Figs. 8.5 to 8.10 are anterior to this first cut, and Figs. 8.12 to 8.20 behind it. With the aim of illustrating as many levels as possible, Figs. 8.11 to 8.17 have been cut at 5 mm intervals using angles 5 mm thick but similar in all other respects to those illustrated in Fig. 7.9. We have attempted as far as possible to restrict key numbers to one hemisphere so that the corresponding structure in the other hemisphere can be clearly seen. Finally, there are illustrations of the cerebellum and the brain stem obtained as shown in Figs. 7.18 to 7.21.
No post mortem examination on a patient who has died as a result of a stroke, or who has a history of a previous stroke, is complete unless the major extracranial cerebral arteries, viz. the internal carotid and the vertebral arteries in the neck, are examined since cerebral infarction may be caused or contributed to by occlusion or stenosis of one of these arteries. They can be opened in situ but this does not really allow of an assessment of the severity of stenosis or the extent of any occlusion by thrombus. By far the best method is to dissect out the principal arteries and then to examine them after preliminary fixation. This dissection should be undertaken before removing the central structures of the neck, viz. the pharynx, larynx etc.
Fig. 5.1 Access to the arteries is greatly facilitated by using a “collar” incision when opening the body, and then reflecting the skin to expose the lateral structures in the neck.
Figs. 5.2 and 5.3 The sternomastoid muscle (arrow in Fig. 5.2) is retracted laterally to expose the common carotid artery (arrow in Fig. 5.3).
As every neuropathologist knows, the brain and spinal cord are often not removed as well as they should be post mortem: it is very frustrating to be asked to undertake a neuropathological assessment on specimens that are so distorted that it is difficult, if not impossible, to reconstitute the situation that existed prior to death. Yet this is precisely the information sought by neurosurgeon, neurologist and neuroradiologist. Since it is not difficult to remove the brain and cord properly, one can only assume that pathologists and mortuary attendants are unaware of the importance of doing so. A common reason for a brain becoming distorted is that it is removed by the mortuary attendant and then left lying on the dissecting bench for some time before the pathologist decides that it should be fixed intact for dissection later. Furthermore, the optic chiasma and the brain stem are often torn, and the lower medulla and the vertebral arteries are often left within the skull. These observations are not meant to be critical of mortuary attendants, but more of pathologists who fail to appreciate the importance of removing the brain themselves, or at least being present when it is being removed.
This volume was first published in 1982. Hume Adams and Margaret Murray have produced an atlas that illustrates basic post-mortem techniques in neuropathology. It shows how to remove the brain, the spinal cord, samples of peripheral nerve and muscle, the eye and the contents of the orbit, the arteries in the neck that supply the brain and the structures in the base of the skull. These structures can then be examined in a sequence that will help to elucidate the sequence of events leading to a person's death. How a brain should be dissected is also illustrated, and there is a final chapter on brain neuro-anatomy.
The base of the skull and its main anatomical features are illustrated in Fig. 2.1. The principal structures that may require to be examined are the pituitary gland, the cavernous sinuses, the trigeminal ganglia and the middle ear. The orbital contents are considered separately in chapter 3.
The technique to be adopted depends on the circumstances of each individual case. Thus the pituitary gland is usually simply removed from the pituitary fossa as shown in Figs. 2.2 – 2.6: in a patient with an adenoma of the pituitary gland, however, or some other tumour that affects this region such as a chordoma, a central segment of the base of the skull should be removed so that the extent of the tumour can be assessed, e.g. to what extent an adenoma of the pituitary gland has invaded into the cavernous sinuses or the adjacent bone. A similar technique should be used in a patient suspected of having thrombosis of a cavernous sinus. The block of bone removed can be decalcified, and sections cut in the sagittal, horizontal or coronal plane depending on the type of lesion that is being investigated.
Using an electric saw with a fan–shaped blade, cuts should be made along the lines indicated in Fig. 2.1: this central block of bone can then be levered away from the base of the skull after cutting through the soft tissue in the nasopharynx.
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