Version May 2024
| Hints for dissection of the intact fetus: |
| 1. Make generous incisions. |
| 2. Examine organs in situ before evisceration – photograph any anomalies and pertinent negative findings. |
| 3. Remove and set aside the thymus and gonads before evisceration because they are small and often difficult to find after dissection. |
| 4. Place the brain into a large, preweighed vessel filled with fixative. Weigh the vessel with the fixative and brain to determine brain weight. |
| 5. After each organ is removed, compare the organ weight with standards. |
| 6. Dissect the heart and great vessels with the descending aorta and lungs after fixation. Document venous return and the ductus arteriosus before dissecting the heart off of the lungs. When opening the heart, open the appendage side from the inferior to the superior vena cava and look immediately for the foramen ovale and the coronary sinus. Probe the coronary sinus to document whether there is a persistent left superior vena cava. Open the right heart along the lines of flow and continue through the main pulmonary artery through the ductus arteriosus and into the descending aorta. Open the left atrium between the left and right pulmonary veins, and then open the left ventricle posteriorly following the posterior descending coronary and then turning anteriorly and opening along the anterior descending coronary keeping in the left ventricular chamber, left of the septum, continuing up through the aortic valve. This will put the papillary muscles on the free wall, give a clean view of the septum (easy to see common ventricular septal defects this way), and maintains the mitral valve intact. Examine carefully for number of valve leaflets in the great vessels. |
| Procedure |
| • Proper respect for the fetus should be maintained during the procedure. Eviscerate by using the classic "Y"-shaped incision. Reflect back the skin, remove the chest plate after cutting through the soft ribs and clavicle. Obtain lung tissue for microbiology. Examine the organs in situ for any situs malformations, ensure all organs are present, and look for any malformations (photograph abnormalities in situ, if identified). |
| • Remove and weigh the thymus, and then submit for histology. Identify gonads, remove, and process. Bluntly dissect up through the neck to the tongue (above the larynx at a minimum), remove as a block from the tongue to anus. Once removed, use a thin probe to document tracheal and esophageal patency (examine for tracheoesophageal fistula). |
| • The organ bloc can be dissected fresh or fixed overnight if tissues are autolyzed. Before tissues are fixed, obtain fresh tissue if needed for special studies. Remove and save the vertebral column. Remove the brain and spinal cord, eyes (intracranially), and pituitary. The brain and spinal cord are best removed by a dorsal approach, which is especially useful in identifying spina bifida and in cases with meningocele, meningomyelocele, and other neural tube defects. |
| • After the scalp is reflected, the cranium can be opened along suture lines. It is sometimes helpful to keep the dura intact. By cradling the head and holding it over a preweighed vessel filled with fixative, the fetal brain can be allowed to fall slowly into the fixative while the cranial vessels and tentoriums are cut. A deep cut into the spinal canal will allow the brain to "slip" into the fixative. Fetal and infantile brains contain more water than adult brains and can therefore be floated in formalin more concentrated than 10 percent. This is achieved by adding undiluted formalin to the formalin solution slowly until the brain floats, thereby avoiding distortion due to fixation. As the brain is being fixed over the following two to three days, it will attain the same density as the formalin and sink. By then, the sunken brain will not distort further and it will not be necessary to add additional formalin. The body should be stitched closed. It is best to ensure the body is presentable. Fetuses who will be buried are rarely embalmed. |
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