Minimally invasive orbital decompression surgery now possible

April 1, 2007

Las Vegas-Successfully performed, minimally invasive orbital decompression surgery for thyroid eye disease requires a clear understanding of the orbital anatomy and pathology of each patient, according to Michæl Kazim, MD.

Las Vegas-Successfully performed, minimally invasive orbital decompression surgery for thyroid eye disease requires a clear understanding of the orbital anatomy and pathology of each patient, according to Michael Kazim, MD.

Dr. Kazim described the importance of both a preoperative clinical review of the patient's photographs before development of thyroid eye disease and also radiographic imaging to determine the nature of the pathology that is causing the proptosis. A meticulous intraoperative technique is needed to maximize exposure and minimize incisions, he emphasized at the American Academy of Ophthalmology annual meeting.

"For patients with thyroid eye disease, the surgical goals of orbital decompression should include restoration of normal globe position, reversal of optic neuropathy if present, and minimization of morbidity, such as sinusitis, double vision, globe ptosis, internal anesthesia, and external scars," said Dr. Kazim, clinical professor of ophthalmology and surgery, Edward S. Harkness Eye Institute, Columbia University College of Physicians and Surgeons, New York.

"The orbital pathology of thyroid eye disease, as it is now understood, includes not just enlarged extraocular muscles but also enlarged orbital fat volume in most cases," Dr. Kazim explained.

Expanded preop evaluation

He said he has expanded the preoperative evaluation of these patients from the conventional examination. "We need to begin to look at the patient's old photographs. They provide an understanding of the patient's expectations and may disclose what the Hertel measurement may have been before development of the disease," Dr. Kazim said. "The examination of the orbital MRI or CT studies should include an analysis of the size and volume of the extraocular muscles and orbital fat, the size and pathology within the paraorbital sinus, and the volume of the lateral orbital sphenoid bone, because they contribute to the potential decompressive effect."

Dr. Kazim discussed the concept of graded orbital decompression, given that one type of decompression does not fit all patients. "Either fat or bone decompression or a combination of the two can be utilized to achieve proptosis reduction in the range of 2 to 10 mm," he explained.

Modified technique

The technique of fatty decompression, which Dr. Kazim and colleagues described about 15 years ago, has been modified to be primarily a transconjunctival approach to the inferior orbital fat compartments. The medial and lateral compartments are debulked deeply. "This is best used for patients with limited proptosis, small extraocular muscles, or to augment the effect of a medial or lateral bony decompression or both," he said.

The removal of fat behind the equator of the globe produces the greatest decompressive effect. The central fat compartment is spared to avoid hollowing of the eyelid.

The medial decompression, which was traditionally performed through external ethmoidectomy or extended intraoral incisions, generally achieves from 3 to 4 mm of proptosis reduction and maximizes decompression of the optic nerve, Dr. Kazim said. The disadvantages are that the procedure may cause sinusitis and is associated with the highest rate of diplopia.

Another approach, described by Norman Schorr, MD, and colleagues, is the transcaruncular approach, with which there is no external incision and no intranasal surgery is required. "However, if there is sinus pathology, this approach is not ideal," Dr. Kazim stated.

Alternatively, the endoscopic endonasal approach to medial decompression performed with ENT surgeons provides increased visualization and more complete posterior exposure, according to Dr. Kazim. He pointed out, however, that instrumentation is expensive and the learning curve is steep.

"When performing this technique, the medial wall of the orbit is exposed [and] the lamina papyracea is removed to expose the periorbita, which is incised above and below the medial rectus muscle," Dr. Kazim said. "The periorbita overlying the medial rectus can also be removed. The ability to monitor the location of the intranasal instruments in three dimensions intraoperatively using the landmark system has been added more recently to the surgical treatment. This allows the surgeon to know where he or she is at all times and to define the extent of the orbital decompression intraoperatively."