Bilateral Dentigerous Cysts

March 1, 2010

Bilateral Dentigerous Cysts

Bilateral dentigerous cysts are uncommon.  A dentigerous cyst, also called an erratic tooth, can developed from one or a conglomerate of teeth, surrounded by a sack or cyst of which the inside is covered with mucous membrane.

Inside the mouth, the number of teeth is normal.  This deformation can be found unilaterally or bilaterally and even in other parts of the body, such as the lymph nodes and testicles.

The origin is located under the temporalis muscle, close to or ankylosed against the temporal bone.  Sometimes, only the cyst is present and no teeth or material can be found.  The cyst usually breaks and drains, forming a chronic drain tract on the cranial edge of the auricle.  Although a foal is born with this deviation, it often remains unnoticed for a long period of time.  Not until the mucous membrane becomes contaminated with bacteria and starts to produce a honey-like secretion, and in a later stage, muco-purulent exudates, does the dentigerous cyst become visible.  This often happens at the age of 1-2 years, but it can occur at a later age.

The symptoms are a chronic dirty ear and/or swelling on the base of the ear, sometimes hard, sometimes fluctuating.  When pressure is added, secretum will come out of the drain tract.  The drain tract is located on the edge of the auricle and runs down the auricle under the temporalis muscle.  Radiographs will confirm the size and location of the erratic tooth.

Treatment for dentigerous cysts is surgical removable under general anesthesia or standing with sedation and local anesthesia.  The drain tract, cyst and erratic tooth must be removed completely for a successful outcome.

Surgery starts with a 6-8 cm skin incision directed ventral from the base of the ear.  The cystic lining should be dissected away from the surrounding tissues and completely removed.  The origin of the cyst is the erratic tooth which is found under the temporalis muscle. Usually the aberrant tooth material is tightly adhered to the temporal bone and can be removed with an osteotome and mallet.

After removing the complete cyst and all of the enhancing tissue, the wound can be closed in three layers, obliterating as much dead space as possible and incorporating a Penrose drain tube.  Dissolvable suture material is used for the muscle and subcutaneous layer and the dermis is closed with a separate non-absorbable suture.  A drain tube can be removed after the hemorrhagic secretion stops.

Field Case: A Yearling QH was referred to the wet lab for evaluation and possible treatment of bilateral dentigerous cysts.  There was a large draining cyst below the left ear and a small similar cyst below the right ear.  Lateral oblique radiographs were taken and it was clearly visible that there was an odontoma present under each temporalis muscle.

Surgical removal of both cysts and odontoma was performed to resolve the abnormality.  The surgery was performed on the horse standing with sedation and local anesthesia.  The lining of the cysts was completely removed, along with the erratic tooth materials which were adhered to the temporal bones.  The surgery site was sutured in three layers and Penrose drain tube was incorporated within the surgical site and vented through a stab incision below the suture line.  The drain tube and suture were removed in two weeks.  Partial dehiscence of the outer suture line occurred 7 days after surgery and the remaining sutures and drain tube were removed 14 days after surgery.  A Three-month follow up revealed compete healing of the surgical area with no signs of drainage or swelling.

B. W. Fletcher, DVM

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