PREOPERATIVE DIAGNOSES:
1.
Intrinsic pontomedullary astrocytoma, evidence of progression following
surgery, radiation therapy and chemotherapy x2.
2.
Cerebellar and cranial nerve dysfunction secondary to diagnosis #1.
POSTOPERATIVE DIAGNOSIS: Progressive intraaxial pontomedullary astrocytoma
with evidence of solid tumor growth and multiple cyst formation extending from
brainstem into cerebellum with worsening neurologic deficit.
OPERATIVE PROCEDURE:
1.
Image-guided CBYON posterior fossa craniotomy and aggressive total
resection of intraaxial progressive low-grade brainstem astrocytoma with
drainage of associated cerebellar cyst.
2.
The use of the intraoperative microscope and microdissection.
3.
Repair of posterior fossa with EnDura dural graft.
4.
Application and removal of cranial fixation device.
5.
Use of intraoperative somatosensory evoked potential, motor evoked
potential and cranial nerve monitoring by Dr. Jaime Lopez.
ATTENDING NEUROSURGEON:
ASSISTANT:
ANESTHESIA:
Michael Edwards, M.D.
Paul Jackson, M.D., Ph.D.
General endotracheal anesthesia.
ANESTHESIOLOGIST:
Pediatric Anesthesia.
PROCEDURE IN DETAIL: Prior to surgery, Xxxxx underwent a contrast-enhanced
image-guided scan placed in the image-guided computer system. She was
premedicated and brought to the operating where careful endotracheal
anesthesia was established. Appropriate lines and monitors were placed,
including an arterial line, Foley catheter, multiple IVs, and compression
hose. Monitors and electrodes were placed for somatosensory evoked
potentials, motor evoked potentials and cranial nerve monitoring. After all
lines and monitors were placed, hyperventilation was begun. The patient was
given dexamethasone 10 mg. She was carefully placed on Mayfield-Kees skull
fixation and turned prone. Laminectomy rolls were also placed at her side.
Her neck was moderately flexed. All bony prominences and peripheral nerves
were padded. She was covered to maintain body warmth. The endotracheal tube
was carefully suspended from the Mayfield-Kees skull fixation.
Her hair was shaved in the occipitocervical area to extend as high as the
ending in her prior incision. We then held her hair forward with a tie and
then draped out the operative area with clean sterile drapes. The skin was
scrubbed for 10 minutes with Betadine soap, painted with alcohol and DuraPrep.
Sterile towels denied, band drape and sterile sheets were applied. The skin
incision had been marked with plans to excise the scar. The skin was
infiltrated with 8 cc of 0.5% local in 1:200,000 adrenaline. The old scar was
then excised with a #15 blade and needlepoint Bovie scalpel. We dissected
down through the prior scar and occipitocervical muscles, separating them off
of the prior occipital craniotomy, which had healed, and separating the
muscles and soft tissue off of the dura in the cervical area from C1, leaving
the spinous process and arch of C2 intact. Deep retractors were placed.
Hemostasis was established with a bipolar cautery on the muscle and soft
tissue, and on the bone with bone wax.
Using an angled curette, we freed the rim of the foramen magnum. Two small
bur holes were made two-thirds of the distance up from the foramen magnum to
the inion using the Midas Rex drill. We then used the high-speed pediatric
Midas Rex Craniotome to perform an occipital craniotomy and the bone was
preserved in normal saline. Hemostasis was established on the dura with the
bipolar cautery and on the epidural space with FloSeal. We irrigated with
warm saline. We draped beyond the operative area with clean sterile towels,
cleansed our gloves, and placed moist Cottonoid patty at the edges of our
craniotomy.
The operating microscope was brought into the field. Using a sharp, the dura
was opened in a V-shaped fashion. The midline sinus had already been occluded
at the prior surgery. We carefully dissected the dura off of the cerebellum
using the microirrigating bipolar cautery and retracted the dura superiorly
with fine silk sutures. We then opened the dura inferiorly in the midline
with a #15 blade and similarly elevated off the cerebellum. It was not
attached at the region of the brainstem. We then retracted the dura with fine
silk sutures and covered the dura with moist Telfa. The Greenberg retractor
was attached to the head holder and the 1/2-inch blade was attached.
Under higher magnification and using the fenestrated suctions and irrigating
bipolar cautery, we first freed the cerebellar tonsils from the region of the
brainstem and identified the tonsillar branches of the posterior and inferior
cerebellar artery. No tumor was noted looking up towards the opening of the
foramen of Magendie. However, based on the image-guided information, we
identified that the tumor sat below the vermis in the midline, slightly above
the region of the obex. Therefore, we used the irrigating bipolar cautery,
fenestrated suction to dissect in the midline of the cerebellar vermis, at
which time we entered a tan to grayish tumor, consistent with the exophytic
component of the tumor coming up from the pons and extending into the
cerebellum. On the right side we entered into the large cyst, which defined a
good portion of the right side of the tumor. The cyst was filled with
xanthochromic proteinaceous fluid and had some hemosiderin staining within the
cystic cavity. We advanced Adaptic over the regions of the cerebellum and
lightly retracted the cerebellum with the Greenberg retracting system. Using
the microdissector and fenestrated suction with the irrigating bipolar, we
began defining a margin between normal brain and tumor. We obtained multiple
biopsies, which were reviewed by neuropathology and consistent with a lowgrade astrocytoma, possibly juvenile pilocytic in origin.
By using a combination of the image-guided system and throughout the procedure
performing sensory and motor-evoked potentials, we carefully checked function
as we began essentially debulking tumor with the Cavitron ultrasonic
aspirator. This allowed us the luxury of defining the lateral margins. As we
were able to work around the lateral margins, we eventually were able to
define an interval between tumor and its extent directly into the pons. Using
very low settings on the bipolar cautery and by debulking the tumor and then
carefully elevating it with small tumor forceps, we were able to define a
plane around the tumor; first laterally and then superiorly. We slowly
defined this plane using microdissection or the microirrigating bipolar
cautery and carefully maintained this plane with Cottonoid patties. By
working from inferior to superior, we were able to begin elevating the tumor
out of the central portion of the pons. Again multiple testing was done, at
one point there was some activity in the 11th cranial nerve. We did not get
any activity in the facial nerve. The tumor extended directly within the
brainstem, but there appeared to be a margin between tumor and surrounding
brain, probably enhanced by the fact that the patient had prior radiation and
chemotherapy. Therefore, we were able to work in this interval and slowly
elevated tumor from the brainstem, removing multiple specimens for permanent
pathology. By continuing to debulk this rather extensive tumor, we were then
able to find the lateral and inferior margins and eventually accomplish what
we thought to be a gross total removal of the tumor extending into the pons.
The tumor was relatively avascular and any bleeding was easily controlled with
the bipolar cautery or application of a small piece of brain cotton for a
matter of minutes.
We then inspected into the cavity inferiorly and noted that there was evidence
of tumor coming from the cerebellar tonsils and extending directly into the
area of the medulla at the junction of the obex. We again were able to use
the Rhoton microdissector, as well as the irrigating bipolar cautery, to
define a margin. We again centrally debulked tumor and rolled this margin
into our view, carefully defining between tumor and brainstem. At the
completion of this rather prolonged and tedious dissection, which ran many
hours, we were able to resect, would what appear to our view, all of the tumor
visible.
Throughout the procedure, warm saline was used to maintain normal
neural transmission. Dexamethasone was given at the initiation of the
procedure and six hours into the procedure.
We carefully inspected along the cerebellar hemispheres. The primary large
cyst and two small secondary cysts had been adequately drained. We could
visualize through the aqueduct of Sylvius and had an excellent view directly
into the pons and the pontomedullary junction.
No further tumor could be identified. There were some areas of hemosiderin
staining due to the cyst, but no definitive tumor was visible to our view by
either angling the patient from side to side or by movement of the microscope
superiorly, inferiorly or laterally.
We again ran multiple evoked potentials, which remained intake. We irrigated
the operative site copiously with warm saline. No bleeding was noted from the
operative site or cerebellum. No hemostatic material was left in place. We
then used a triangular piece of the EnDura, which we anchored in place with
interrupted 4-0 Nurolon suture and sutured to the dura with running 4-0
Nurolon; performing a watertight closure, before placing our last sutures
filling the posterior fossa with warm saline. No bleeding was noted from the
posterior fossa. We obtained a watertight closure. We then irrigated the
dura and muscles with warm saline and bacitracin solution. We placed a large
piece of DuraGen over the suture line, followed by fibrin glue.
We then closed the muscle and fascia in multiple layers with interrupted #0
Vicryl suture; second, a more superficial layer with interrupted 2-0 and 3-0
Vicryl suture, and the skin with running 4-0 Monocryl. Xeroform gauze, Telfa
and Tegaderm dressings were applied. The drapes were removed. The patient
was turned supine and taken out of the head holder. The recording equipment
was removed. The patient was noted to be breathing adequately and a decision
was made to extubate the patient in the operating room and transfer to the
Pediatric Intensive Care Unit extubated. The patient was extubated and was
noted to be ventilating without difficulty. She was therefore transferred to
the Pediatric Intensive Care Unit in stable condition. At no time during the
procedure was there any significant hemodynamic instability. On some
occasions there were some slight changes in either heart rate or blood
pressure; all of which were very transient and responded to our stopping
dissection or irrigating with warm saline solution.
At the end of the procedure, it would appear that a gross total resection of
tumor was obtained. The patient tolerated the procedure well. There were no
intraoperative complications. Needle, sponge, and Cottonoid count was
correct. Specimens to pathology consisted of intramedullary brainstem tumor.
I was the primary surgery with operative assistance of our chief resident.