Image guidance surgery - Is it useful to the orbital surgeon?

Image-guided surgery (IGS) refers to a surgical system that is able to incorporate pre-operative imaging to a real-time correlation of a surgical instrumentation within the surgical field. The use of IGS in otolaryngology and neurosurgery has gained considerable acceptance and is especially useful to the endoscopic sinus surgeon in sphenoid, posterior ethmoid, and frontal sinus surgery, pterygopalantine tumor surgery, and cerebrospinal fluid leak closure. Although IGS has only recently been applied to complex orbital and sino-orbital surgery, it is not new to the field of medicine. Stereotactic surgery in early 1900s evolved from animal neuro-functional experimentation to human neurosurgical use in 1947 (Gildenberg, 2004). In 1978 an American physician, Russell Brown, is credited with the inventing the use of CT scans in stereotactic surgery. In the 1990s, frameless stereotactic systems allowed surgical instrumentation to be tracked while imaging was displayed. IGS begins with obtaining pre-operative high quality imaging (CT or MRI scans) and then digitally importing this data into the IGS workstation. Once this data is imported into the IGS system, the surgeon then is able to establish three-dimensional visual localization of surgical instrumentation and the position of the surgical instruments in relation to established anatomical landmarks. The surgical instruments can then be tracked via infrared optical trackers or an electromagnetic tracking system during the operation. Optical tracking involves infrared light for tracking of instruments using a camera and optical sensors on instruments and reference frame (line-of-sight must be maintained). Practically, the IGS workstations should have the ability to display the position of the chosen surgical instrument (suction devices, forceps, probes, and powered instrumentation) in relation to its three-dimensional position on the CT images (axial, sagital and coronal). Endoscopic images can also be displayed alongside the CT images in a multiplanar format. Ideally, the use of this technique should be accurate to approximately 2–3 mm and easily operated by the surgeon with some need for technical assistance (Kingdom and Orlandi, 2004). Widespread surgical experiences have helped develop useful applications of IGS in orbital surgery. IGS provides intra-operative assistance to the surgeon dealing with complicated anatomy. For the orbital surgeon, the bony anatomy of the orbit provides a unique challenge. The orbit, in particular the posterior orbit, is often a technically challenging space to enter; furthermore the delicate structures of the orbit require that any surgery in this region minimizes adjacent trauma. As IGS is used more readily the applications for its use in orbital surgery continue to grow. Current applications in orbital surgery include orbital fracture repair (early, late and revisional), orbital decompression with removal of bone, excisional and incisional biopsies of orbital tumors, optic nerve biopsy, optic canal decompression, surgical repair of lost extraocular muscle, surgical management of fronto-orbital and spheno-orbital mucoceles, and complex lacrimal surgery. It should be emphasized that IGS is especially useful in revision surgery with altered anatomy. At the University of Colorado, we have found IGS especially useful in certain cases. Complex or revision orbital fracture repair is often a challenge for the orbital surgeon. IGS allows the surgeon to deal with complex, altered anatomy and also allows transposition of normal anatomy to help reconstruct the orbit and preserve normal orbital volume (avoid post-operative enophthalmos). We have also found IGS useful in the surgical treatment of compressive optic neuropathy secondary to thyroid eye disease. Although transcaruncular decompression is often used for posterior removal of bone from the medial wall, transnasal endoscopic posterior medial wall decompression with IGS assistance provides an elegant option for direct visualization for bone removal and navigation of the posterior orbital apex (Fig. 1). Finally, IGS is especially useful in our practice in the minimally invasive endoscopic surgical management of sino-orbital mucoceles. Figure 1 Muliplanar image showing coronal, axial, sagital and endoscopic view and localization during orbital decompression for thyroid eye disease. In conclusion, IGS is useful to the orbital surgeon in certain orbital disorders. Indications include altered boney anatomy, orbital apex pathology, and optic nerve or optic canal pathology. The advantages of IGS include the potential for decreased complications and more complete disease management. It is also valuable to the surgical educator as a teaching tool. Disadvantages include over-reliance on technology (using the device as an anatomy seeker instead of anatomy confirmer), increase surgical time, and the cost of acquiring the equipment. It is believed that as familiarity with IGS increases, so will its application in orbital surgery.