This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The neck is the seat of some very peculiar cystic tumors and fistulae which are connected with developmental defects. They are either lateral or median in location. The lateral originate from the visceral (branchial) clefts, while the median are connected with the thyroglossal duct. The visceral clefts are depressions between the visceral arches. These arches, five in number, spring forward from each side of the embryo to form the neck region. Sometimes these arches are called branchial arches from the fact of their going to form the branchiae or gills of fishes and some of the other lower orders of animals.
Fig. 188. - Foetus, 25th day (after His). Showing branchial (visceral) arches and clefts or furrows.
The first visceral arch divides into two parts, a maxillary part forming the upper jaw and a mandibular part forming the lower jaw. Defects in the maxillary arch producing harelip and cleft palate have already been described. Two of the ear bones, the incus and malleus, are also formed by the mandibular portion of the first visceral arch.
The second visceral arch forms the stapes, the styloid process, the stylohyoid ligament, and the lesser horn of the hyoid bone.
The third visceral arch becomes the body and greater horn of the hyoid bone. The fourth and fifth visceral arches blend and form the soft structures of the side of the neck.
The first visceral cleft, called the hyomandibular cleft from its being between the hyoid bone and the mandible, forms the middle ear and Eustachian tubes from its inner portion and the external auditory meatus from its outer portion. The membrana tympani is the remains of the membrane which stretched across from one arch to the other. Cervical fistulae are formed by the persistence of a visceral cleft. As the first visceral cleft persists normally in the structures already named, it in itself does not form pathological fistulae, but congenital fistulae are sometimes encountered in the external ear which are the remains of the clefts between the tubercles of which the ear is formed.
Fig. 189. - Points of opening of sinuses originating from the thyroglossal duct and branchial clefts. (Modified from Sutton).
Cervical fistulae or sinuses may extend either completely through, from the surface to the pharynx, or may open internally or externally, or be closed at both ends, in which last case the contents accumulate and form a cervical cyst.
Fistula arising from the second visceral cleft open externally opposite the thyrohyoid space in front of the sternomastoid muscle. Internally they open into the recess holding the tonsil.
Fistulae arising from the third and fourth visceral clefts open externally lower down nearer the sternoclavicular articulation in front of the sternomastoid muscle and internally in the sinus pyriformis. The persistence of the third and fourth visceral clefts internally may produce pharyngeal diverticula, as already noted in discussing that region.
In attempting the cure of cysts and fistulae due to persistence of the visceral clefts it is evident that as they are lined with a secreting epithelium this must be destroyed or removed, or a recurrence will take place. In attempting to dissect them out one must be prepared to follow them through the structures of the neck to the pharynx inside. It is needless to say this may be a serious procedure.
Fig. 190. - Median cervical pouch or cyst arising from the thyroglossal duct. - Marshall's case.
Fig. 191. - Median cervical (thyroglossal) cyst. - Author's case.