Wednesday, March 23, 2011

Canine fossa trephination


The key to any successful Endoscopic sinus surgery lies in clearing the residual disease from the maxillary sinus cavity. The diseased mucosa of the maxillary sinus cavity could cause formation of pus, eosinophilic fungal debris, polyps etc. These disorders dont reverse after performing a wide middle meatal antrostomy. They need to be cleaned out physically which can be rather difficult via the middle meatus as the anterior wall of the maxillary sinus and the high lateral walls are virtually not reacheable via the natural ostium. It is hence advisable to remove as much as diseased mucosa from the maxillary sinus in order to facilitate the rapid return of the sinus mucosa to normal. This is where maxillary sinus trephination has a role to play.

Optimal location for Canine fossa traphination:

Anatomical studies have shown that the best place to insert the trocar in the canine fossa is at the junction of the mid pupillary line and a horizontal line drawn through the floor of the nasal vestibule. At this site a 5mm hole can very easily be drilled thorough which a 4 mm nasal endoscope can easily be passed.

Illustration showing the exact location for placing the trocar in the canine fossa

Indications for canine fossa trephining:

  1. Grade III maxillary sinus disease that cannot be addressed adequately via the enlarged natural ostium
  2. Presence of excessive polypoidal mucosa within the maxillary sinus
  3. Presence of mucopyoceles
  4. Presence of a large antrochoanal polyp

Before proceeding with canine fossa trephining a large middle meatal antrostomy should be performed. A 70 degree endoscope can be used to inspect the interiors of the maxillary sinus cavity. This inspection will also help in grading the maxillary sinus disease.

Grade I – Normal or slightly oedematous mucosa
Grade II – Oedematous mucosa with small polypi without eosinophilic mucous
Grade III – Presence of extensive polypi and thick tenacious mucin

Anatomy of the canine fossa:

The canine fossa is the thinnest portion of the anterior wall of the maxillary sinus. Hence it is easy to breach this area and enter into the sinus. Boundaries of the canine fossa include:

  1. Canine eminence formed by the canine tooth – medial
  2. Root of the zygoma – laterally
  3. Alveolar process of maxilla - inferiorly
  4. Infraorbital foramen with the infraorbital nerve superiorly

The trephining of the canine fossa can be performed sublabially. After successful trephination using the trocar has been performed the opening can be widened using a burr. The opening should be wide enough to permit insertion of a 4 mm nasal endoscope. The maxillary sinus can be visualized from both angles i.e via the natural ostium using a 70 degree endoscope and via the opening in the anterior wall of maxilla. One port can also be used to introduce instruments to remove the diseased mucosa and pent up secretions.

Complications: Are very few if anatomy is respected.

  1. Facial numbness
  2. Numbness of upper dentition
  3. Pain over the cheek
  4. Hematoma over cheek

Most of these complications are self limiting and resolve within the first week after surgery.

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