2. Tubulodermoids.
—These are largely connected with obsolete canals and ducts. It is a great service which Sutton has rendered in proving, apparently beyond the possibility of doubt, that the central canal of the nervous system is really of intestinal origin, and may be regarded as a disused segment of the primary alimentary canal. He has also shown how it behaves occasionally as do other functionless ducts, and that cysts and dermoids in connection with it are to be thus explained. He and others have also shown the anterior as well as the posterior communication of these canals, and the pituitary body are to be regarded in this light as the same formation of lymphoid tissue around an obsolete canal which we see in Luschka’s tonsil close by, and in Luschka’s gland at the other extreme of the canal.
Fig. 72
Solid dermoid escaping from pelvis. (Original.)
Fig. 73
Congenital dermoid cyst of pelvis. (Ahlfeld.)
The primary alimentary canal was a continuous tube lined with a continuous layer of columnar epithelium. That portion connected with the yolk sac develops into the intestine, the balance into the central nervous canal. Portions of this canal are in postnatal life absolutely obsolete; others persist in a rudimentary condition. Dermoid cysts and dermoid tumors develop in connection with each of these. In some there is a large central cavity; others are almost absolutely solid. Thus we find dermoids in the coccygeal region, which have been variously regarded as sarcomas, adenomas, etc., which are really of origin as stated above and should be considered simply as dermoid tumors. Most of these project outwardly; some of them arise and develop within the pelvis. Dermoid cysts and tumors are also met with in connection with the rectum—sometimes between the rectum and the bladder, and between the rectum and the spine. Dermoid tumors are also found in connection with the pituitary body. These sometimes develop within the cranium, or, again, protrude perhaps into the orbit, perhaps into the pharynx.
Thyroid dermoids are tumors of great interest. They develop sometimes about the craniopharyngeal canal, which may be detected as a small canal in the macerated sphenoid bone of a fetus, and which before birth is filled with fibrous tissue. It connects with a recess in the middle line and at the base of the skull, presenting in the pharynx, which is often referred to as the bursa pharyngea. It is around this recess that the lymphoid tissue known as the “pharyngeal tonsil” develops. It may be thus expected that the roof of the pharynx should be the occasional site of dermoids. It is from the pharynx or the floor of the mouth that in vertebrates the thyroid body arises. In higher forms it becomes dissociated from the pharynx and shifts its position. The thyroid body is developed around the thyroid duct, which first appears as the thyrohyoid duct, which later becomes divided, that portion in relation with the tongue becoming the thyrolingual duct, the remaining portion persisting as the thyroid duct. These are present about once in every ten subjects, according to Sutton, the canal when persistent being lined with epithelium. When the extremities of these ducts become occluded retention cysts may form. In the same way dermoids of the tongue are formed, similar to those occurring on the scalp. These are frequently mistaken for sebaceous cysts. They may be unilateral, central, or even bilateral. The lingual duct is also of interest, because it would appear that certain cases of epithelioma of the tongue arise along this duct, and perforating malignant ulcer of the tongue is thus produced. Dermoid tumors of the lingual or thyroid ducts resemble in structure the thyroid body. The thyroid duct may also be detected in many adults running from the isthmus of the thyroid body to the posterior aspect of the hyoid bone, and surrounded by muscle tissue. Sometimes the space usually occupied by this duct is represented by a series of detached bodies known as accessory thyroids. These are not infrequently the seat of cysts, sometimes of considerable size. (The accessory thyroids often enlarge when the main thyroid has been extirpated for disease.) Thus cysts in close relation to the hyoid bone are common. Some of them grow slowly, while others grow rapidly and contain much fluid. Many of them are unilateral, and are often mistaken for enlargements of one lobe of the thyroid. Cysts growing from accessory thyroids are often filled with papillomatous masses, and are occasionally the seat of malignant degeneration.