DATE OF OPERATION: MM/DD/YYYY
PREOPERATIVE DIAGNOSIS: Chiari malformation with large syringobulbia and myelopathy.
POSTOPERATIVE DIAGNOSIS: Chiari malformation with large syringobulbia and myelopathy.
OPERATIONS PERFORMED: Suboccipital craniectomy, C1 and C2 laminectomies, Chiari decompression with microdissection technique, and expansile duraplasty with bovine pericardium, intraoperative somatosensory-evoked potential monitoring.
SURGEON: John Doe, MD
ANESTHESIA: General.
FINDINGS AND DETAILS OF OPERATIVE PROCEDURE: On the day of surgery, the patient was brought to the preoperative holding area where IV access was obtained and mild IV sedation was administered. She was given prophylactic intravenous antibiotics and then was brought back to the operative suite. While on the hospital gurney, she underwent an uneventful induction of general anesthetic with placement of an endotracheal tube. The endotracheal tube was secured in place, and once secured, additional IV access was placed, including central venous access and arterial access. A Foley catheter was inserted and then SSEP monitoring leads were placed, and baseline studies were obtained. TEDs and SCD hose were applied. The patient’s head was then placed in the Mayfield head holder, set to a pressure of 70 pounds using 3-pin fixation, and then the patient was placed on the operating room table on top of gelatin rolls in the prone position with the head flexed to expose the occipitocervical region. She was secured to the table in this position. We made sure that we had at least two fingerbreadths between the patient’s chin and sternum, and we made sure that we did not significantly kink or occlude her venous return from her brain. We inspected all pressure points and appropriately padded them and then secured her to the table.
At this point, 1-inch shave was made from the patient’s inion down to the midcervical region in the midline. The area was then sterilely prepped in the standard fashion using Betadine scrub followed by 70% alcohol followed by povidone-iodine paint. We allowed the paint to dry, and once dried, the area was sterilely draped in the usual fashion. Using a sterile indelible marker, we marked a planned incision extending just caudal to the inion down to approximately at C3 cervical spinous process by palpation. We then infiltrated this area of the skin with local anesthetic, and then used a #10 scalpel to incise the skin down to the subcutaneous tissues. We maintained a plane in the midline and then proceeded to dissect through the avascular raphe between the bellies of the occipital and cervical paraspinal musculature.
As we continued to dissect down this plane, we came upon the occipital bone and used monopolar electrocautery, periosteal dissectors, and Penfield #1 dissector to skeletonize the soft tissues off of the bone. We then continued down caudally until we came upon the C2 spinous process and create a subperiosteal plane with the paraspinal musculature in the C2 process. We dissected down until the lateral mass of C2 and C3 were identified on either side, and then we proceeded to expose the junction between the base of the occipital bone at the level of the foramen magnum with the C2 bone. Interestingly, as we proceeded with this dissection, we found a congenital malformation of the C1 arch. The patient appeared to have a spina bifida of the C1 arch, in fact only a hemi arch was identified. It was present on the right side; it did not come to midline. We also identified what appeared to be a partial C1-2 congenital fusion with the remaining remnant of the C1 arch on the right side.
After we meticulously skeletonized this entire area, we found the prevertebral fat just medial to the vertebral arteries on either side. We placed our cerebellar retractors to maintain this visualization and then felt we did not have to dissect any further laterally, as we now had exposed a generous region to decompress the Chiari malformation. The occipital bone was exposed and approximately 5.5 to 6 cm of bone was exposed in the X-axis, being approximately 2.5 cm to 3 cm off the midline on each side.
At this point, we then used the Midas Rex drill utilizing the AM-8 drill bit and thinned the occipital bone to the thickness of eggshell until the underlying dura was visualized. We then used the combination of 1 mm and 2 mm Kerrison rongeurs to remove the remaining bone and expose the underlying posterior fossa of dura. The craniectomy extended approximately 2.5 cm to 3 cm off the midline on each side extended just caudal to the torcular and transverse sinuses bilaterally, and extended down to the foramen magnum and out laterally at the level of the foramen magnum until the occipital condyles were identified on either side. We then proceeded with the use of AM-8 drill bit to create troughs in the C2 bone at the junction of the lamina and the lateral masses, and we proceeded to remove the remnant vestigial C1 ring on the right side. In doing so, we identified the underlying ligament from the foramen magnum extending down to the C2-3 junction where we were able to get a Penfield #1 dissector as well as a Woodson dissector between the planes of this ligament in the dura, and then used bipolar electrocauteries to coagulate this ligament and incise it sharply with tenotomy scissors. We reflected it laterally to expose the occipitocervical dura. At this point, we had obtained meticulous hemostasis and then proceeded to open up the dura.
The remainder of the procedure was now done with microdissection technique under microscopic visualization. Using a #11 scalpel, the dura was incised at the level of the C2 lamina in the midline. We then used tenotomy scissors to extend it rostrally. We immediately, upon opening the dura, identified cerebellar tonsils which were extended down to the C2 vertebral bone. As we opened the dura rostrally, we were very careful to inspect it prior to incising it, thus preventing any injury to any arterial vessels that could lie within proximity to the dorsal dura. As we came to the occipitocervical junction, we then expanded our incision to create a V or Y type incision from this point going out over the cerebellar hemispheres to just within a couple of millimeters of the transverse sinus. The leaflets were then elevated using 4-0 Nurolon tack-up sutures. We did also identify a very small persistent circular sinus at the base of the foramen magnum upon opening the dura, which was controlled with bipolar electrocautery and medium hemoclips.
At this point, we then tacked up the dura to meticulously complete the decompression under microscopic visualization. Using microscissors, bipolar electrocautery, and microdissection technique, we were able to open up multiple separate arachnoid adhesions that were densely adherent to the cerebellar tonsils, posterior inferior cerebellar artery, and with multiple attachments to the occipital dura as well. As we freed these up, we were able to release more CSF flow, but realized that there was still a significant amount of adherent tissue at the obex. We then used microdissection technique and proceeded to open up the arachnoid at the obex to gain access to the floor of the fourth ventricle. We identified cord up into the fourth ventricle and then used bipolar electrocautery to slightly coagulate the base of the cerebellar tonsils back to open up the obex and allow for free drainage of spinal fluid from the fourth ventricle into the subarachnoid space. Upon opening up the arachnoid and coiling back a part of the cerebellar tonsils, we did now see free flow of spinal fluid emanating from the fourth ventricle and coming out of the region of the foramina of Luschka and Magendie and into the subarachnoid space.
At this point, we felt that an adequate decompression had been accomplished and we proceeded with our expansile duraplasty. A 6 x 8 cm piece of Dura-Guard bovine pericardial graft was used to sew into the open dura to provide an expansile dural graft for our closure. It was reapproximated to the patient’s own dura using a running 4-0 Nurolon suture. Just prior to completion of the closure, we did irrigate the entire system out with normal saline, we saw no significant bleeding, and then we performed multiple Valsalva maneuvers to remove intracranial air and to ensure no additional bleeding had occurred. After the dural graft was sewn in, the edges of the dural graft were sealed with Tisseel fibrin glue, which was then also covered with a piece of DuraGen. At this point, the posterior fossa and underlying spinal cord appeared to be well pulsatile. No additional spinal fluid was seen emanating from the incision, and we proceeded with our soft tissue closure.
The paraspinal musculature and fascia were then closed with multiple layers using interrupted 0 Vicryl sutures. The subcutaneous tissues were then closed with inverted 2-0 Vicryl sutures and the skin was closed with a running 3-0 nylon suture, and it was covered with antibiotic ointment, Telfa gauze, and secured with staples. The estimated blood loss in the surgery was 100 mL. No intraoperative complications occurred, and SSEP monitoring and lower cranial nerve monitoring remained at its baseline throughout the surgery. The patient remained hemodynamically stable throughout the surgery. At this point, she was taken out of the Mayfield headholder, placed back on the hospital gurney, and was allowed to awaken. She was moving all her extremities and at her neuro baseline. She was then taken to the recovery room in stable condition.
