Comparative Medicine Branch

Virtual Mouse Necropsy

Step 10: The Lungs

Gross Anatomy of Thoracic Organs

1. Esophagus
2. Thyroids
3. Trachea
4. Mediastenial lymph nodes
5. Thymus
6. Heart
7. Right lung (apical, azygous, cardiac, diaphramic lobes)
8. Left lung

Removing the Thoracic Organs

Your necropsy is almost over.  Using the esophagus as a handle, pull the lungs and attached organs up through the cervical girdle and continue up to where the trachea and esophagus disappear near the larynx. It is important to sever the esophagus and trachea as far up as possible in order to remove the thyroid glands successfully. Now you can remove the whole structure from the thoracic cavity.

General Examination

You have the heart, thymus, lungs, thyroid, esophagus, larynx, mediastinal nodes, and trachea in front of you in one package. All need to be examined.

1. Remove the esophagus from the system and check for any blockage by inserting a syringe in one end and flushing with saline or preservative.
2. The thyroids are flanking the trachea on the anterior end of the system and should have a  tannish color. Check to see if the color is consistent and they are symmetrical in size and shape. The parathyroids are not visible grossly at this point. They are located around or within the thyroids, and can only be seen histologically.
3. The thymus lies directly on top of (or ventrally to) the heart. In younger animals that haven't gotten past adolescence, the thymus will be rather large. As the animal ages, the thymus shrinks. It should be a whitish-translucent color without any inconsistencies in color. In athymic mice, there is no thymus. So, don't worry if you can't find a thymus in an immunosuppressed mouse.
4. The mediastinal nodes lie dorso-laterally to the thymus and can be enlarged. These little lymph nodes, when enlarged, may look like thymic lesions, so be careful.

Lung Examination

1. Larynx
2. Thyroids
3. Trachea
4. Apical Lobe
5. Azygous Lobe
6. Cardiac Lobe
7. Diaphramatic Lobes
8. Left Lobe

Now examine the lungs. Using a syringe full of preservative, insert the needle into the trachea and fill the lungs. Not only does this preserve the lungs in a way that benefits histology, it will also give you a 3-dimensional area to examine for possible lesions. The lungs should have a pink bubble gum color. The surface should be smooth and fresh looking. Examine each lobe (see diagram) to see if there are any lesions in junctions or hidden from view. Place the whole structure in fixative. The lungs are not as dense as the fixative and will float on the surface. If, for some reason, the lungs sink, something is wrong and it should be noted. The only thing that you removed in this whole process is the esophagus; the lungs, heart, thyroids, trachea, thymus, and mediastenial nodes have remained together.

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