Dissection Of Fresh Lungs

Dissection from Hilus The pulmonary arteries and bronchi are opened from the hilus toward the periphery of the media-stinal surface of the lung. Subsequently, the lungs are cut into several sagittal slices, that is, parallel with the mediastinal surface. This method permits study of many cross-sections of bronchovascular units and gives a good overall view of the parenchyma. Unfortunately, the continuity of the organs is lost so that it may be difficult to identify the original site of individual slices. More important, vessels and bronchi running in a more frontal plane cannot be opened without at least partly destroying the slices.

Dissection from Incisions Along Lateral Surface of Lung After separation from the mediastinum, a bronchopulmonary cuff should remain on the lungs. The hilus of the lungs with this cuff is held in the hand of the prosector. An incision is made from the apex to the base of the pulmonary lobes along their longest lateral axis. For the right middle lobe, this axis lies almost in the horizontal plane. The incisions into the upper and lower lobes reach toward but not into the hilus and are connected by a third incision that lies at a right angle to the first and second. This third incision divides part of the wall of a main pulmonary artery, which usually shines through the pleura in the interlobar fissure close to the hilus. One blade of a pair of scissors is introduced into this opening and the pulmonary arteries are opened radially in all directions. The cuts made by the scissors should include the periphery of the pulmonary parenchyma and the parietal pleura so that the lungs can be laid out well (Fig. 4-2). Subsequently the bronchial tree is dissected in the same fashion (Fig. 4-3). During this last maneuver, the prosector must cut through many pulmonary artery branches.

This method requires more practice than the dissection from the hilus, but it leaves the dissected lung in continuity and permits easy reconstruction of the original position of pulmonary lesions. If the lungs had been separated from the main bronchi too close to the hilus, it may be difficult to leave the hilar structures intact. In order to preserve the continuity of most arteries and bronchi, this method can be combined with dissection from the hilus (3).

Histologic Sampling For routine histologic sampling, a container can be used with three compartments for the right pulmonary lobes and two compartments for the left lobes. Whatever method is used, the origin of every lung section should be identified. For electron microscopic studies, rapid collection and fixation of samples is recommended. For fixation prior to routine autopsy, see Chapter 1 "Immediate Autopsies for

Fig. 4-1. Larynx, trachea with carina, and esophagus with anterior half of trachea and adjacent main bronchi removed. Note perforation of carcinoma of esophagus into left main bronchus at carina.

Special Laboratory Procedures such as Electron Microscopy, Cytochemistry, and Tissue Culture" and "Needle Autopsies."

WET FIXATION OF LUNGS Formalin fixation of lungs with a perfusion apparatus (see below) provides excellent specimens, both by reconstituting the size of the lung at full inspiration and by providing good fixation for histologic study. A prudent approach is to perfuse one lung and dissect the other in the fresh state to obtain material for microbiologic study and for smears, for instance when Pneumocystis carinii infection is suspected. Also, pulmonary edema and embolism are best assessed in the fresh lung.

If no perfusion apparatus is available, lungs can be reinflated with 10% formalin solution through the main bronchus. About 2 L of formalin solution is needed for an adult lung. The inflation can be done with a large syringe or, better still, from a bottle 30-50 cm above the specimen. Subsequently, the main

Fig. 4-2. Cut surface of lung dissected from incisions along lateral surfaces of lobes. Hilus is left intact. Pulmonary artery tree has been opened lengthwise in radial fashion.

bronchus is clamped and the lung is floated in a formalin bath. It should be noted that the organ shrinks again during this period.

Removal and Preparation of Lungs Prior to Wet Fixation

For most special studies of isolated lungs, it is essential not to lacerate the organ during removal. We usually first produce a pneumothorax through a small parasternal incision. In many instances, the chest plate can then be removed safely. If one wants to protect the lungs even better, the anterior attachments of the diaphragm to the rib cage should be incised so that the hand of an assistant can be introduced to hold back the lung during removal of the chest plate. The remaining rib ends should be covered with a thick towel or plastic sheet because the severed bone may lacerate the pleura (and also the skin of the persons working on the cadaver!). Before the lungs are removed, adhesions must be carefully dissected as close to the parietal pleura as possible. This is particularly difficult at the posterior base of the lower lobes, where adhesions are frequently encountered. If adhesions are extensive, one may attempt to remove the lungs with the parietal pleura that must be dissected from the bony and muscular parts of the chest wall. Small rents in the pleura should be tied off or sealed with wound spray ("artificial skin").

Connection of the lung with the perfusion apparatus is greatly facilitated if an extrapulmonary bronchoarterial cuff is left attached to the lung. It is also possible to leave the lungs

Fig. 4-3. Same lung as in Fig. 4-2. Bronchial tree has been opened lengthwise in radial fashion, sacrificing continuity of some overriding arteries.

attached to the trachea and thus perfuse them simultaneously. Similarly, pulmonary angiograms can be prepared by leaving the lungs attached to the main pulmonary artery. Both procedures can be carried out in situ.

Before perfusion, mucus and purulent material should be suctioned from the bronchi. If this cannot be done successfully, the lungs should be perfused through the pulmonary vessels.

Fixation Time Complete perfusion fixation requires about 3 d. Consolidated and fibrosed lungs may need longer. Plugging of bronchi may completely prevent proper expansion and fixation. In such an event, the affected portions of the lung will not inflate.

Formalin Perfusion Techniques (Pressure Fixation) In the previous edition of this book, several apparatuses were described and illustrated. More recently (4), a fixation apparatus for surgically obtained lungs has be described that undoubtedly would also be suitable for autopsy lung. With this apparatus, the perfusion pressure can be set in a range from 15-95 cm H2O. However, for routine purposes, our cascade perfusion system which has been in use for more than 25 years, has been most satisfactory. Therefore, only this system and its operation shall be described here (5,6). The apparatus can also be used to perfuse livers (5) and other organs such as heart and kidneys, either from the autopsy service or from the surgical pathology laboratory.

In the perfusion apparatus shown in Fig. 4-4, the fixative cascades through stacked plastic containers and flows through nozzles tied into the main bronchus or the trachea. An electric pump causes the fixative to circulate. As fixative, we often use modified Kaiserling's solution (see Chapter 14) but neutral buffered formalin is suitable also. Angiograms can be prepared before or after fixation. Prior to the perfusion fixation, we flush the lungs with 10% buffered formalin. This helps to keep the actual perfusion solution reasonably clean. After 3 or more days of continuous cascade perfusion, the lungs are sliced with an extra-long knife (see below), which is needed to avoid cutting marks. It should be noted that the perfusion apparatus shown in Fig. 4-4 was assembled in the Mayo Clinic engineering shop; the complete system is not commercially available but modifications undoubtedly can be built without too much difficulty.

OTHER WET, GASEOUS, AND DRY PRESERVATION METHODS Pressure-free perfusion fixation at predetermined states of expansion (7), fixation with formaldehyde gas, or formalin steam fixation have been used in the past, mostly for research purposes. These and other methods have been illustrated in the second edition of Current Methods of Autopsy Practice (8). They include air-drying of lungs, which is obsolete but still would be justified if no other preservation method is available. After air-drying, the macroscopic features of the lungs are remarkably well-preserved but histologic samples are unsatisfactory. Museum specimens have been prepared by this method, using infiltration of lungs with paraffin or diglycol stearate; this probably has no place in current autopsy practice.

SLICING OF FIXED LUNGS We use a special knife and slicing board (Fig. 4-5) The cork slicing board is mounted in a metal tray where the draining formalin solution collects. The knife has a 78-cm long blade that in many instances permits the whole lung to be cut with one uninterrupted pulling motion. This ensures a smooth and even cut surface without knife marks. This knife also works well to prepare even slices of livers or large spleens. The lung usually is cut in the frontal or sagittal plane in slices about 1.5 cm thick. For frontal sectioning, the lung is placed so that the hilus is uppermost. We usually make the first cut immediately adjacent to the hilus. If the cut section is to be along the axis of a bronchus, the knife is guided along metal probes or glass rods previously inserted into the major airways. For the preparation of large and very thin slices, gelatin infiltration is required (see below under "Paper-Mounted Sections").

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