6
The Respiratory System
180
The respiratory system extends from the nares to the most distal alveolar spaces. Although in life many infections occur in the upper tract, the major- ity of respiratory conditions relevant to the post mortem are found in the lung. Many ultimate causes of death involve the pulmonary tree, and this makes careful investigation of the lungs especially important. Most of the major pathological findings such as tumours or infections will have been identified pre mortem or found at the time of evisceration, but it is as well to follow a routine for dissecting the airways to avoid overlooking relevant pathology. For example, it is important to examine the pleural cavities for fluid, adhesions, or pneumothorax and the pulmonary arteries for emboli at the appropriate time in every case in order that these findings are not passed over and therefore neglected. These have been discussed fully in Chapter 3 on general evisceration and are not repeated here. Obviously, flexibility of technique is also important in order to obtain as much infor- mation from the post mortem examination as possible and avoid potential problems from hazards such as tuberculosis. Flexibility also allows optimal impact at the time of demonstration. This chapter outlines:
• Routine examination and dissection of the lungs
• Special techniques used in lung dissection
• Dissection in cases of lung transplantation
• Special techniques used in dissection of the nasopharynx, sinuses, and larynx
The Lungs
As mentioned previously, removal of the lungs for dissection is achieved by cutting through each of the main bronchial stems distal to the carina with a large pair of scissors or PM40 (see Fig. 4.7). In many cases it is not par- ticularly important where these cuts are made, but if a proximal tumour is present, or when it is crucial to examine the lung parenchyma closely (e.g.,
with possible interstitial lung disease or in cases of pneumoconiosis) the cut should be made toward the carina, leaving as long stump of bronchus as possible. In this way the lungs can be inflated and fixed to allow the subse- quent morphological assessment to be optimised. It is almost impossible to interpret collapsed lung tissue sections accurately and conditions such as emphysema or interstitial lung disease cannot always reliably be recognised from examination of unfixed, often squashed, uninflated lungs. This is also useful for distinguishing between arterioles and venules as the anatomical relationships are better preserved. In cases of suspected glue sniffing or chemical inhalation a whole lung can be removed to an airtight container and retained for analysis before the solvent evaporates.
External Examination
Normally the lungs weigh 350 to 400 g each in an adult (see also Appen- dix), but may weigh well in excess of 1 kg in cases of severe cardiac failure or other severe acute diffuse lung pathology such as pneumonia or diffuse alveolar damage. The weights are recorded prior to dissection to obtain a quantifiable measure of the amount of intraalveolar fluid, particularly oedema. As will be recalled, there are three lobes on the right and two lobes with a lingula on the left. Each lobe is served by a main lobar bronchus, which branches into the segmental bronchi, which in turn split into bron- chioles. The following descriptions are documented as if dissecting one lung, but apply to both left and right lungs equally.
Internal Examination
Dissection of the Airways
It is conventional to open the airways with a medium to large pair of round- ended scissors from the large to small airways, from medial to lateral to include all lobes and segments opening along the branches as they are encountered (Fig. 6.1). In this way it is possible to gain an impression of the parenchymal appearance and texture and to approximate the airway calibre. Very small sized lung tumours (especially small cell carcinoma) are among a limited group of malignancies in which a miniscule primary may be associated with (or even present with) widespread metastases and there- fore careful inspection is warranted in such cases.
Apical disease such as old tuberculous cavities or fungal balls can also be demonstrated. A rough guide to the presence of chronic obstructive pul- monary disease (COPD) can also be made by assessing how far peripher- ally the airways can be opened. The further the passages can be opened the more severe the COPD. A more accurate and demonstrable way to assess COPD is to produce Gough–Wentworth slices of inflated and fixed lung as described below. The latter enhances the appearance and can be examined
with a hand lens. Air spaces greater than 1 mm are considered emphyse- matous. Once the airways have been opened the parenchyma is inspected to look for fibrosis, consolidation, tumours, scars, or cavities. The paren- chyma should be squeezed or massaged and any pus or fluid expressed should be noted.
Dissection of the Vessels
The lung is now turned over so the outer visceral pleural surface can be reexamined. The horizontal and oblique fissures are then identified and the soft tissue deep within the fissure is dissected superficially to expose the outer surface of the wall of the hilar segment of each pulmonary artery. A scissor cut at this point into the lumen will allow access to the rest of the pulmonary tree by opening the vessels in a peripheral direction, rather like the method for opening the airways (Fig. 6.1). Obviously here it is impor- tant to look for emboli and atheroma; the latter is associated with raised pulmonary pressure/pulmonary hypertension. Large emboli associated with sudden death are usually found at the evisceration stage; emboli identified when opening the smaller arteries may well have less significance. It is also possible if required to open the airways and vessels both from either the Figure 6.1. The pulmonary airways and arterial tree are demonstrated by tracing the systems from the hilum peripherally with medium or small scissors. It is cus- tomary to open the airways from the medial aspect and the vessels from the outer aspect. The airways are demonstrated here on the left and arteries on the right. In practice both systems are opened more distally than they appear in this photograph.
hilar or outer aspects but there will obviously be a significant amount of cross-cutting and loss of control over the procedure.
Slicing the Lung
Once the airways and vessels have been dissected it is useful to make a hor- izontal slice through each lobe with a large-bladed knife such as a brain knife in order to inspect the rest of the parenchyma. This is done on the dissecting board by laying the lung flat with the medial side down toward the board. A sponge can then be placed over the outer surface of the lobe to be cut to protect the securing hand from inadvertent injury during slicing (Fig. 6.2). It is occasionally preferable to make large horizontal slices through the whole lung rather than opening the airways and vessels as described previously. This displays any large mass lesion in the lung, such as a large bronchogenic carcinoma, well and preserves all the local rela- tionships for demonstration.
Histology
When blocks are required for histology, and consent is available for this, they should be taken from each lobe of each lung even if no obvious
Figure 6.2. The lung is sliced parallel to the dissecting board with the upper surface controlled with a sponge. (Courtesy of Mr. Dean Jansen, Whittington Hospital.)
pathology is identified. Identification of the origin of these blocks is aided by following a system of cutting particular shapes of tissue for a particular site as described in Chapter 13. The tissue blocks should be of the usual size, approximately 3 ¥ 2 ¥ 0.4cm, and need to be fixed well before pro- cessing and sectioning. Extra blocks will need to be taken from any masses identified or areas of interest. Remember that it is better to retain and fix excess tissue at the time of post mortem if there is any possibility of it being relevant to the examination, as it is impossible to retrieve later. This does not of course mean that all tissue retained needs to be processed and sec- tioned if it turns out that it is not required. Histology is essential in cases of industrial related diseases relevant to the cause of death, especially if this has not been documented and established during life, and methods for assessing asbestos exposure are described later in this chapter.
Immunohistochemical methods for differentiating pleural metastases from primary malignant mesothelioma are sometimes required and these should follow routine surgical pathological principles and are not discussed here.
Special Techniques
Method for Opening Airways and Vasculature Avoiding Transection A method has been described for examining the lungs that allows demon- stration of both the bronchi and pulmonary arteries without potential problems caused by transection [4]. This is a modification of the method described above which opens the airways on the hilar (medial) aspect and the vessels from the outer (lateral) aspect. With the isolated lung in the palmar aspect of the hand, the visceral pleura is incised opposite the hilum in the exposed transverse (or equivalent) fissure. The vascular supply to the lower lobe can be opened with blunt ended scissors from the main pul- monary distally as described previously. Next the lingula or right middle lobe arteries are dissected similarly by cutting the visceral pleura between the upper and lower lobes (oblique fissure) on the left or between upper and middle lobes (transverse fissure) on the right. Then the lung is turned over to demonstrate the hilar side. The upper lobe arteries should then be opened from this aspect. This is intended to expose the arterial system without disrupting the airways. The next step is to open the airways to the middle, lingual, and lower lobes from the main bronchus on the medial (hilar) surface. The final stage is opening of the upper lobe airways from the hilum on both sides. It should be possible to avoid transection of the upper lobe vessels when opening the airways by advancing the scissors at an angle, underneath the arteries as the bronchi lie below the arteries in this lobe. It should be remembered, however, that local relationships between airways and vessels do show some variation and slight modifica- tions may be necessary.
Inflating a Lung
It is very useful and occasionally essential to examine the lung parenchyma in a fixed inflated state so that an accurate diagnosis and assessment of interstitial disease can be made. Three main methods are employed, all either introducing fixative via the trachea into both lungs in continuity, or fixing via the main bronchus of an isolated lung. Should this be required it should be remembered that one lung could be dissected in the usual way at post mortem while the other is retained and the following technique per- formed on the latter. The left lung is recommended for inflation because the left main bronchus is longer than the right and this should aid cannu- lation and perfusion. It is important to preserve the pleural surface in order that the fixative does not leak out during fixation. The bronchus or trachea is cannulated and this cannula is fixed firmly in place with a ligature. The lung is placed in a bath of 4% or 10% formalin or formal saline and the cannula is connected to a hose running from a container of the same fixa- tive placed at a height from the bath. This produces a head of pressure that allows fixative to enter the airways and perfuse these distally. A pressure of about 25 to 30 cm of water is recommended, and perfusion is stopped when the pleural surface becomes smooth. Elastic recoil within the lung(s) may push some fixative out, but this is usually not a problem. The lungs are left in this state for 24 to 48 hours after which they can be washed in water and sliced using a large brain knife with the slices lying 1 to 2 cm apart in a parasagittal plane. Alternatively a meat slicer can be used to produce thinner slices. Slicing should be performed in a suitable area such as a safety cabinet to reduce the risk of exposure to formalin fumes.
The Pump System
The second method involves a similar setup but instead of introducing the fixative by hydrostatic pressure, a constant pressure pump can be attached and this also allows recycling of formalin through the system. Slices of lung tissue can be made in a manner similar to that described earlier after 24 to 48 hours.
Formalin Vapour Method
The third main method that has been described for inflating and fixing the lungs is to fix the lung(s) with formalin vapour. A rubber stopper is plugged into the main bronchus and this is then pierced by a needle through which the lung is inflated with formaldehyde gas at a pressure of 40 to 50 mmHg.
The gas is produced by filling a large container with 40% formadehyde solu- tion and bubbling air through it. Once the lung is filled with gaseous fixa- tive it again is floated on a bath of liquid fixative and covered in a soaked cloth. After 48 hours of fixation, slices can be made in the same way as
described above. In practise the previous methods are preferred because of the hazards of using formalin vapour.
Cases with Abundant Luminal Contents
All of these methods of lung inflation/fixation are made easier if the airways are patent and the lumina of the airways clear. If there is much pulmonary oedema or consolidation one should consider removing the bronchial mate- rial or performing the same technique as described in the previous section, but perfusing the lung with fixative via a pulmonary vessel. This also allows intraluminal material to be retained in the specimen, which may be desir- able in some circumstances. There are in fact many other variations on these themes with regard to wet or dry fixation, as well as freezing, but these are not all described here.
Producing Lung Slices
The lung slices produced by any of the methods described can be stored in appropriate sealed containers but for permanent records barium sulphate impregnation is recommended. A slice of fixed lung is placed in a barium nitrate solution (75 g of barium nitrate dissolved in 1 litre of warm water) for 1 minute. This is then removed and placed in aqueous sodium sulphate solution (100 g/l). This is repeated until tissue is opaque and greyish white, which renders the tissue opaque and allows for better visualisation. Quan- titative measurements of changes such as emphysema are also easier to calculate.
Gough–Wentworth Slices
Lung tissue slices can also be paper mounted to produce Gough–
Wentworth slices. Fixed tissue slices are washed thoroughly and then placed in a heated gelatin solution and subjected to partial vacuum until the gelatin penetrates the tissue. The slices are then incubated at 35°C for 48 hours.
The gelatin is then allowed to set and is frozen overnight. Sections 400mm thick are cut with a large section microtome and refixed in 10% forma- lin–acetate solution. There follows another washing step and then the section is covered with a second gelatin solution which in turn is covered by a sheet of Whatman no. 1 filter paper. The whole aggregate is dried and the process is complete (Fig. 6.3).
Microbiology of the Lung
It is important to sample any specimen for microbiological analysis early on in the post mortem examination although contamination either during the procedure or caused by post mortem bacterial colonisation or growth is difficult to avoid. It is suggested that all pneumonic processes identified at post mortem should prompt the prosector to consider removing lung
tissue for culture. Several methods are available, with the easiest involving removing a small wedge of peripheral lung tissue and placing it in a sterile container. There may well be contamination with such a basic method and searing the lung surface and sampling a deeper area of tissue approximately 1 to 2 cm3will potentially give more relevant results. It is possible of course to sear the surface and swab the underlying tissue and send this sealed in a sterile tube. An alternative for pulmonary microbiology involves freezing the whole lung and producing large section imprints onto agar plates for culture Zanen-Lim and Zanen suggest that there may be increased likelihood of sampling error with smaller pieces [6]. When tracheal specimens require investigation either a ring of tissue or a swab of secretions should be sampled. Virological samples should be collected into suitable containers.
Figure 6.3. A paper-mounted slice of lung prepared following the Gough–
Wentworth technique. This is particularly useful for demonstrating interstitial and obstructive pulmonary disease.
In all cases the appropriate request forms should be completed, with details of the investigations required listed and including notification regarding any potential hazard.
Smears and Imprints
Smears or imprints of airways tissue or fluids may also be made onto glass slides for direct microscopy after staining with appropriate stains such as Gram, periodic acid–Schiff, Grocott, and Ziehl–Neelsen, among others.
Care should always be taken when handling unfixed, potentially hazardous tissue.
Examination of Cases of Known or Suspected Pulmonary Tuberculosis
Whenever there is a possibility of tuberculosis, special procedures must be followed, although the scientific basis for these procedures has recently been questioned. Despite this, it is generally accepted that inflation and fix- ation almost entirely eliminate the risk of contamination in such cases.
There are many general principles that are worth remembering when con- fronted with a high risk post mortem. These have been discussed in detail in the opening chapter, but a few of the important factors are repeated here.
It is essential to limit the number of staff exposed to a minimum and to reduce the time of exposure to an absolute minimum. As the main risk is inhalation, the main protection for the prosector is a microfilter face mask or respiratory equipment. The area of work and equipment used should also be limited. In the case of tuberculosis it may be appropriate to fix the lungs promptly and to leave dissection to a later date (usually after several hours or days). If the risk is not apparent until during the post mortem examina- tion then the lungs can be inflated with formol saline before dissection and left to fix in a container full of formalin fixative for the intervening period.
This has been described more fully in an earlier part of this chapter. With adequate respiratory protection, however, predissection filling by formalin is not considered essential and in fact is no longer recommended (RCPath guidelines 2003). The examination should be performed in a standard fashion. It was previously suggested that the thoracic block be removed as the last part of the post mortem examination so that all other systems are dealt with beforehand. It was also recommended that the rib cage be left intact until the end of the examination and Letulle’s en masse method was not recommended.
Pulmonary Radiology
It is rare for post mortem radiology to be considered necessary, but this is occasionally very useful for comparison with in vivo X-ray films. Even more
rarely is post mortem bronchography or angiography necessary, but again this can sometimes be extremely instructive. The general principles for post mortem respiratory radiology are outlined as follows:
– Cannulate the appropriate vessel or airway.
– Tie a ligature.
– Introduce warmed gelatin–barium sulphate mixture at necessary pressure.
– Cease at point of resistance.
– Take X-ray films.
Specific procedures are best carried out after fixation as outlined below.
Pulmonary and Bronchial Angiography and Bronchography
These can be performed in situ, but are usually performed on organs removed from the body and are really applicable only to inflated intact lungs. The technique is rather fiddly and will require a degree of patience, care, and experience. Depending on the system to be studied either cannu- late the pulmonary artery(ies), veins, bronchi, or bronchial arteries. All of the following require previous fixation in an inflated state in order to allow the medium to get access throughout the lung. The medium to be used is usually a gelatin–barium mixture but the optimal concentration of gelatin will depend on many factors and it should be tailored to each individual case.
Pulmonary Arteriography
If the lungs need to be left in situ prior to arteriography, for instance when a tumour is present, the pulmonary artery can be cannulated with a large- bore needle and barium contrast medium introduced. With isolated lungs, the main bronchus should be cannulated and the lung inflated with air under a pressure of arpproximately 20 mmHg. The barium–gelatin mixture is warmed to 60°C and introduced under pressure (in excess of 70 mmHg) into the main artery. After the vasculature is filled, resistance will be felt and the procedure should be stopped. It is important at this stage to keep the lung warm so that the gelatin does not set too soon.
Venography
For the venous system a similar technique can be followed but it is helpful to leave the left atrium in continuity in order to aid cannulation of the pul- monary veins.
Bronchial Arteriogram
It is also possible to perform bronchial arteriography, either in situ or on isolated lungs. For injection in situ the axillary, common carotid, internal mammary, vertebral, and thyrocervial trunk arteries need to be ligated. The aorta also needs to be ligated just above the aortic valve. Similar gelatin–
barium mixtures are introduced through the coeliac axis and stopped when the peripheral small subpleural vessels are filled. With isolated lungs the bronchial arteries are cannulated just above and behind the main bronchus.
An injection pressure of approximately 150 mmHg will be required and it will also be necessary to inflate the lungs with air or carbon dioxide at the same time.
Bronchography
Bronchograms can be produced in an essentially similar manner but in this instance contrast is introduced into the central airways and care must be taken to avoid overfilling.
Miscellaneous
Further estimates of air content, blood volume, and post mortem pul- monary function studies are possible but these methods are more of historical interest and so rarely performed that the reader is referred else- where for these details [3]. Likewise preparation of bronchial or vascular casts and museum pieces is described in other texts.
Lung Transplantation
The principles for assessment of post mortems after lung transplantation are similar to those at other sites and the aims are to establish the events leading to death, identify any features of a rejection process, identify any complications of the operative procedure or treatment, and look for evi- dence of the disease leading to transplantation. The examination may be complicated and the possibility of referring the case to a centre with expe- rience and a special interest should be seriously considered. Alternatively, the undissected individual fixed organs may be referred to the specialist centre but information may be limited by the fact that inter-organ rela- tionships and pathology may be lost. In any case it is important that a thor- ough examination be performed, as the findings are extremely important for educational, counselling, and audit purposes.
Before evisceration all external sutures and drains should be inspected and if tubing remains in place this should be sent for microbiological culture. During evisceration all cavitary fluids should be collected and measured and any foci of infection sampled for microbiology. It is recom-
mended that the thoracic organs be removed as a complete pluck rather than as individual organs and that this pluck should be removed and dis- sected last, as appropriate time and care need to be dedicated to this section.
First the neck structures can be examined in the routine manner and removed. Then the descending aorta and oesophagus are dissected and removed, leaving the larynx, trachea, lungs, and heart together. The next stage will depend on whether one or both lungs have been transplanted and which lung if only one. When dealing with combined heart and lung trans- plants the cardiac dissection described on p. 160 is followed and then the lung(s) are examined as described below.
As revascularisation is required in all cases, except single lung transplants on the right, and involves anastomosis of the left internal mammary artery (IMA) to the donor bronchial artery, this site needs to be assessed before evisceration of the thoracic organs. The sternum is removed with extreme care and the posterior surface inspected to note the absent left IMA. The origin of this vessel should then be identified along the left subclavian artery and its route traced to the anastomosis. The integrity of this anastomosis is checked before proceeding to the lung (and heart) dissection.
With lung lone double transplants, the heart should be separated from the lungs by dissecting the innominate veins and superior vena cava and then dividing the pulmonary veins and arteries close to the hila of the lungs.
It is important to take care when separating the lungs from the trachea because there may be significant fibrosis and it is easy to damage the local structures and disrupt the tracheal suture line. The larynx and trachea are opened along the posterior wall down to the carina. Assess the tracheal or bronchial suture lines. Inflate one lung as described above. The other lung can be examined in the usual way but 1- to 2-cm thick slices are recommended. The cut surface should be examined for infection, diffuse alveolar damage, oedema, vascular lesions, or mass lesions. Samples should be taken for bacteriological/viral investigation as described previously.
Blocks should also be taken for histological examination from anastomosis sites (including the left IMA and bronchial artery anastomosis) with longi- tudinal segments of tissue taken across the joining area, from each lobe of each lung and the pulmonary vessels (donor and recipient). Fresh frozen tissue should be kept for any future investigations that may be nec- essary. It is important to verify that consent has been obtained for tissue retention.
Other Special Techniques
Pneumoconiosis
All industrial injury benefits from occupational lung disease in the United Kingdom are currently dealt with by the Medical Boarding Centre, Respi- ratory Diseases and the pneumoconiosis panel no longer exists. The routine
examination of the lungs of deceased workers in industries such as mining, potteries, and quarries (for which examination of the lungs was required) ceased as from 1986/7 with the abolition of the death benefit. All present cases concerning asbestos exposure and mesotheliomas are considered by the Medical Boarding Centre. Any doubts in the diagnosis are followed up by local experts. In the United States a special group within the American College of Pathologists known as the pneumoconiosis committee is involved with the pathological aspects of pneumoconiosis cases.
Asbestos Body/Fibre Demonstration During the Examination
There are several ways to attempt to identify asbestos at post mortem [1, 2, 5]. The easiest is to slice the lung parenchyma with a blade and to express pulmonary fluid onto several clean glass slides (Fig. 6.4). A cover slip can be placed over this wet preparation and the slide examined microscopically for ferruginous asbestos bodies. Alternatively, the exposed lung tissue can be scraped with the blade and the material applied onto a clean glass slide and examined microscopically in the same way. If asbestos bodies are seen then previous exposure is confirmed but the following methods may still be required for documentaion and quantification of the degree of morpho- logical abnormality. If asbestos is not identified then this does not exclude previous exposure and further sampling is necessary.
Figure 6.4. Asbestos (ferruginous) bodies expressed from the lung of a patient dying with a malignant mesothelioma.
Histological Sections
An additional method is to examine formalin-fixed paraffin-embedded lung tissue for asbestos bodies. Asbestos bodies tend to aggregate in the same areas as carbon dust pigment. They are more easily demonstrated in thick (30mm) sections that are unstained or have a light counterstain. Because the ferruginous bodies contain ferroprotein complexes it is possible to iden- tify this coating utilising Perl’s iron stain (described in Chapter 13), and this is particularly useful if small numbers of bodies are present. The pneumo- coniosis committee of the American College of Pathologists recommends examining 15 blocks of lung tissue in these cases with a minimum of 1 block per lobe, especially in subpleural and basal areas.
Digestion Techniques
The next technique involves utilising the robustness of the fibres by digest- ing the encompassing lung tissue. This can be very useful, as not all fibres are coated in an iron–protein complex and those that are not may be invis- ible on routine microscopy. Digestion techniques allow these fibres to be detected and also allow quantification. For this technique standard blocks of lung tissue are taken and then weighed accurately before being exposed to sodium hypochlorite solution for digestion. The remainder of the tissue block is weighed and then dried to constant weight at 110°C to obtain a wet/dry ratio. After digestion, fat is removed by extracting with diethyl ether and the resultant suspension filtered through a Millipore membrane (0.22mm pore size). The filter is split into a sample for electron microscopy and another for phase-contrast microscopy. The latter allows measurement and counting of fibres. Alternatively, lung tissue samples can be macerated with concentrated potassium hydroxide and the resuspended residue can be inspected directly in a Fuchs–Rosenthal counting chamber which allows the number of fibres and asbestos bodies to be counted.
Electron Microscopy
It has been shown that these light microscopic methods significantly under- estimate the number of fibres that are present in a particular lung sample.
If accurate quantification is required then electron microscopical analysis is necessary. Measurements are made at around ¥20,000 magnification.
Some of the different types of asbestos fibres can also be distinguished using X-ray diffraction analysis.
Environmental Lung Research Group
In the United Kingdom it is possible to send off lung specimens (part or complete) to the Environmental Lung Research Group based at Llandough Hospital, Penarth, Wales for asbestos fibre typing and levels (as well as other fibrous minerals such as talc and silica). The findings are useful in doc-
umenting levels and therefore establishing whether occupational or just background exposure is present in any particular case. Permission will be required from the coroner and/or relatives but as the coroner should be notified of deaths associated with industrial disease, there will usually be local protocols for dealing with such cases.
Diatom Testing in Drowning
Although this is primarily the province of forensic medicine, this tool may be of use on occasion in an attempt to establish whether a body has been immersed in water before or after death. Close cooperation and communi- cation is needed between the mortuary and the laboratory performing the test so that appropriate samples and containers are used. The basic theory and method are briefly considered here but interpretation is not always straightforward. Whole texts have been devoted to the detail and applica- tion of this technique. The fundamental idea is to compare the diatom profile of the water in which a body has been discovered with the presence (if any) of similar diatoms in various tissues removed at post mortem.
For this method a significant sample of water is taken from the presumed drowning site and examined for diatoms. Diatoms are unicellular micro- scopic forms of algae covered with a wall of silica. If none are present then examination of tissue is obviously futile. Tissue samples should be taken from the lung, brain, kidney, liver, and bone marrow. Every effort should be made to avoid contamination with other tissues such as skin and gut con- tents, but after removing the organs, the latter are washed in a strong stream of water (tap water is said to contain much too few diatoms to cause any confusion). A decent sized block of tissue (as much as 4 cm3) should be dis- sected using a sterile scalpel blade, sampling from within the organ. For bone marrow the sternum is washed and cut with a saw, enabling the central marrow to be scooped out of the interior. These tissues are then sent to the laboratory for diatom analysis. This involves digestion in nitric acid, dilu- tion centrifugation, and microscopy of the deposit produced. Identification of significant numbers of diatoms in the peripheral tissues, particularly bone marrow, indicates that death occurred after immersion in the water. The lungs should be examined first because if no diatoms are present here there will almost certainly be none in the other sites.
Examination of the Upper Respiratory Tract
Nasopharynx
Formal examination of the upper airways is often excluded from the post mortem, partly because significant pathology is infrequently found in the nose or nasopharynx and also because these are difficult areas to examine critically. Rarely a tumour arising in these areas may conceal itself but man-
ifest by metastasising widely and hence in cases where disseminated tumour is found with no obvious primary lesion, it is essential to check this loca- tion carefully.This can be done in most cases by a cursory glance from below while removing the tongue as described in Chapter 3. In others more time needs to be taken to examine this area carefully, but usually no further dis- section is necessary. If further investigation is warranted then a good view of the nares and nasopharynx can be gained by chiselling off the central areas of the skull base that overly them. For an even more optimal view it may be worth considering halving the base of the skull after reflecting the skin and soft tissue further over the lower skull. A saw is then used to divide the occipital bone into two halves and then the sawing is extended anteri- orly and inferiorly to separate the rest of the skull base.This is clearly poten- tially disfiguring and in this situation it is prudent to obtain consent from relatives before embarking on the procedure.
Sinuses
The sinuses can also be inspected from above by sawing through the skull base in a manner similar to that just described. All four main groups of sinuses (frontal, ethmoidal, maxillary, and sphenoidal) can be inspected via this route. Examination of the sinuses should be performed by an experi- enced operator owing to the risk of seriously damaging the face of the cadaver. After removal of the brain, the skin incisions made previously are extended if necessary to allow the anterior and posterior skin flaps to be reflected as far down as possible. Next the skull base is divided in the midline by sawing with a manual or electric saw. When this division is com- plete, the two halves can be prised apart using a chisel or T-piece. The sinuses will be exposed and can be fully opened from the medial side.
Further chiselling at the thin bone of the skull base may be required. Any pus or neoplasm needs to be removed and dealt with in the appropriate way. For infection analysis swabs should be taken and sent for microbio- logical study whereas tumours can be examined by sampling tissue for his- tology. Alternatively one can removed the complete block of tissue using a oscillating saw and decalcifying it before sectioning and staining. For a more rapid inspection of the sinuses, it is usually adequate to chisel away at the skull base to expose the underlying tissue and gain a limited view of the sinus cavities.
Larynx
In cases in which the larynx is a major site of interest the larynx and trachea should be removed in the usual way but left intact for more detailed exam- ination rather than opened posteriorly in the manner described previously.
Examination follows the same principles as those used for dissection of a surgical laryngectomy specimen in the dissection room but obviously the margins are not of the same importance. The first stage is to cut through
the larynx by a midline posterior approach. This will expose the mucosal surface of the anterior structures. The larynx can then be cracked open by breaking the hyoid bone and thyroid cartilages by lateral pressure using both thumbs. The epiglottis and other supraglottic structures, vocal cords and glottis, and subglottis are inspected and the lesion of interest identified.
Note the size, macroscopic appearance, and location of the lesion. Slice through the lesion with a scalpel and assess the depth of invasion and any infiltration of surrounding tissues. Assuming consent has been obtained, take longitudinal blocks for histological examination. The blocks may well need to be decalcified prior to sectioning (as described on p. 255). Local lymph nodes that may be involved should also be examined and, if appro- priate, blocked for histology.
If the larynx and local cartilages are very calcified it is worth considering decalcifying the whole larynx before it is examined. Following the same pro- tocol as that described earlier, slices can be made for macroscopic and micro- scopic examination and any direct bony infiltration identified more easily in continuity with the lesion. It also allows full-thickness slices and blocks to be made without distortion from difficulty in slicing through hard, calcified tissues.
Examination of the respiratory system is summarised as follows:
– Check for a pneumothorax.
– Collect pleural fluid if present.
– Check for a thromboembolus.
– Weigh and inspect the lungs.
– Dissect the airways.
– Dissect the vessels.
– Slice the lobes.
– Massage and inspect the cut surface.
– Use special techniques as necessary.
References
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2. Gold C. Asbestos levels in human lungs. J Clin Pathol 1969;22:507.
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