Fig. 15.1
Key steps in the successful enucleation of a group E eye. Immediately after the peritomy, Tenon’s capsule is being spread widely and deeply between the rectus muscles with a curved Stephens scissor (a). 2 cc of a 1:1 mixture of short- and long-acting local anesthesia is deposited in the retrobulbar space using an irrigating cannula (b). Dry orbit immediately after removing the iced-saline-filled test tube that had provided gentle pressure to the apex of the orbit for 10 min (c). 20 mm conical SST Medpor® implant being inserted into the orbit (d). Fig. 15.1 (continued) The predrilled holes and orientation for the rectus muscles are indicated by a skin marker. The four rectus muscles are attached to the predrilled Medpor implant (e). Approximately 3–4 more mattress sutures will be used to approximate the tissues (f). Six to eight vertical interrupted sutures across the horizontal mattress sutures will provide strength to Tenon’s closure. The appearance of the child immediately after the drape has been removed following the removal of the left eye (g). Note the lack of ecchymosis or lid edema. A simple patch will be used for only for the first 24 h
The four rectus muscles are then sequentially isolated with muscle hooks, imbricated with a double-armed 5-0 vicryl suture, and transected from the globe at their insertion sites. A suggested sequence of muscle disinsertion is (1) inferior rectus, (2) lateral rectus, (3) medial rectus, and (4) superior rectus. When passing needles through muscle tissue, the angle of passage should always be parallel or away from the sclera to avoid inadvertent globe perforation. A longer muscle insertion (about 5 mm) is left at the insertion of either the medial rectus or lateral rectus muscles (surgeon’s preference) to allow for some traction on the globe (with an Adair clamp) during transection of the optic nerve. As each muscle is disinserted, the ends of the vicryl suture are secured to the drape with a labeled steri-strip to prevent tangling during the rest of the procedure. The superior oblique muscle is then isolated with a muscle hook using a sweeping motion behind the superior rectus insertion and transected from the globe. The inferior oblique muscle is located in the inferolateral, anterior orbit by sweeping the muscle hook away from the globe toward the orbital rim; this muscle is highly vascular and should be cauterized with bipolar cautery before transection. A visual inspection is then performed of the anterior and equatorial sclera surfaces to ensure that there are no adhesions remaining between the orbit and sclera (other than the optic nerve).
The scissors chosen to transect the optic nerve varies with the preference of the surgeon. In general, we prefer a pair of slim-profile scissors with long tips which are slightly curved (e.g., long Metz or Metzenbaum scissors). It is our impression that the exaggerated 15° curve on the enucleation scissors increases the risk of sclera perforation and reduces the ability to extend the tips into the posterior orbit. Some surgeons utilize an enucleation snare to cut the optic nerve although we do not have a great deal of experience with this instrument because of the induced crush artifact. For similar reasons, we also do not recommend clamping of the optic nerve prior to transection. Another option is to sever the optic nerve under direct visualization through a superior orbital approach, utilizing a small upper lid incision [3].
15.4.1 Long Optic Nerve Stump
Certain surgical steps can facilitate obtaining the minimum 15 mm of optic nerve stump recommended in all enucleation cases for retinoblastoma. An Allis Adair artery clamp (same width as the rectus muscle insertion) can be used to exert gentle traction on the globe during this critical step. Our personal experience is that gentle traction applied to the 5 mm of rectus stump will serve to “lengthen” the nerve in the orbit exposed to the scissors. An initial spreading movement adjacent to the optic nerve with the scissors will open the posterior Tenon’s layer and allow the tips to enter the retrobulbar space. While maintaining tension on the Allis clamp, the scissors tips are mobilized along the medial orbital wall and moved in a vertical motion to palpate the optic nerve. If the surgeon cannot feel the optic nerve with this motion, the nerve may be either below or above the scissors tips due to globe rotation. The surgeon should then find the medial rectus insertion and rotate the globe so that it is located in the correct anatomic position. It should also be kept in mind that the optic nerve follows a temporal to nasal route as it plunges toward the orbital apex. Once the optic nerve is palpated, the tips of the scissors are opened slightly (with the optic nerve between the tips) and pushed nasally/posterior toward the medial wall. With the scissors tips pushing toward the posterior belly of the medial rectus muscle, posterior pressure is maintained and the scissors are closed around the optic nerve, transecting the nerve in one decisive motion. The tension on the globe should release at this point, confirming that the optic nerve has been successfully transected. The globe will now move forward and you will note some attachments of orbital fat and soft tissues holding the globe within the orbit. The scissors are then used to gently lyse these attachments fairly close to the globe to avoid cutting any motor nerves within the muscle cone.
After the globe has been removed from the orbit, it is placed on a separate Mayo stand which has been set up with several instruments including a corneal trephine, small Castroviejo forceps, and Westcott scissors. Hemostasis within the orbit is obtained with a tonsil ball (i.e., spherical gauze pad) soaked in epinephrine (1:1,000 concentration) and activated thrombin. An assistant gently holds the tonsil ball within the muscle cone, while the globe is prepared for pathologic examination. Another option for hemostasis is to use a test tube filled with a frozen-slush saline solution to tamponade the orbit (Fig. 15.1c). Using the epinephrine-soaked tonsil ball (or ice-filled test tube) as a tamponade for approximately 10 min results in little postoperative swelling or bruising. There is typically no need for a pressure patch and the dressing can be removed the following day after outpatient surgery.
15.4.2 Harvest of Fresh Tumor for RB1 Testing or Other Research Uses
On the Mayo stand, the optic nerve stump should be measured and inspected for any gross pathologic changes. A posterior optic nerve margin is obtained prior to opening the globe to avoid any tumor contamination by artifactual clumps of tumor cells. The posterior stump of optic nerve is prepared by marking the surgical margin with ink, and then transecting the optic nerve with a razor blade 4 mm behind the sclera. This posterior optic nerve margin should be placed into a jar of 10 % buffered formaldehyde and submitted separately. The globe is then inspected for any evidence of extraocular tumor extension, and the location of the inferior oblique muscle is used to aid in orientation of normal globe landmarks (e.g., macula). The location of the base of the tumor is outlined with a marking pen on the sclera, determined either with transillumination or from preoperative fundus drawings. Then, a small sclero-choroidal window is created, adjacent to the tumor base near the equator with a 6 to 8 mm corneal trephine. Once the opening into the vitreous chamber is established, tumor tissue should be gently removed with forceps and scissors. For genetic testing, the sample is sent fresh in saline in a Petri dish. Samples of the tumor for research purposes are placed into the appropriate vials and transported immediately to the lab. It is best to leave a hinge on 1 side of the scleral flap so that it can be closed with 1 or 2 suture(s) following the removal of tumor sample. The globe should be placed in a second jar of formalin (separate from the optic nerve stump) and be allowed to fix for at least 24–48 h before sectioning.
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