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Surgeons' Corner

A Surgical Approach to Orbitotomy Using the Bone Scalpel: A Case Report

Ross, Lindsey MD; Bose, Swaraj MD; Chu, Ray MD

Editor(s): Patel, Vivek R. MD; Subramanian, Prem MD, PhD

Author Information
Journal of Neuro-Ophthalmology: September 2020 - Volume 40 - Issue 3 - p e62-e64
doi: 10.1097/WNO.0000000000000952
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A 79-year-old woman with a history significant for cataract revision and breast cancer treated through lumpectomy, chemotherapy, and external beam radiation 5 years earlier presented with left upper eyelid ptosis and binocular diplopia. An MRI of the brain and orbits exhibited a left orbital retrobulbar intraconal mass at the orbital apex with mass effect on the lateral and superior rectus muscles and diffuse heterogenous calvarial bone marrow changes (Fig. 1). She was referred to ophthalmology and neurosurgery for further evaluation.

F1
FIG. 1.:
Preoperative MRI brain and orbits: (A) T2 in axial view (B). T1 precontrast in axial view (C). T1 postcontrast in axial view. D. T2 in coronal view (E). T1 postcontrast in coronal view exhibiting a well-circumscribed lesion in the left superomedial orbit extending to the orbital apex that encases the superior rectus muscle and laterally displaces the superior oblique muscle. The mass inferiorly displaces the optic nerve but does not appear to originate from the optic dural sheath. The mass measures 2.7 cm anteroposteriorly by 1.5 cm superoinferiorly by 1.7 cm transverse.

On evaluation, she exhibited a left pupil sparing third nerve palsy with significant left ptosis and inability to adduct the left eye. Her best-corrected visual acuity was 20/30 and 20/50, respectively, in the right eye and the left eye. Pupils were 3 mm in size with brisk reaction, and there was no afferent pupillary defect seen in either eye. Color vision was recorded using HRR color plates, and she identified 24/24 and 21/24 color plates correctly in the right and the left eyes. The intraocular pressures were 12 and 16 mm Hg. Hertel's ophthalmometry on a base of 110 was 15 and 18 mm with a 3-mm proptosis in the left eye with mild resistance to retropulsion left eye. The palpebral fissures were 8 mm in the right eye and 1 mm in the left eye. Rest of the anterior segment examination including the conjunctiva, cornea, anterior chamber, lenses, and vitreous was within the normal limits in both eyes. Motility evaluation revealed 8–10 prism diopters (PDs) of exotropia (XT) and 25 PD of left hypertropia (HT) in the primary position. There was a limitation of adduction, elevation, and depression in the left eye with complete ptosis left upper eyelid. A dilated fundoscopic examination revealed a healthy optic nerve head with a C/D ratio of 0.5/0.6, with normal blood vessels and bilateral age-related dry macular degeneration, L > R. The rest of her neurological examination was within normal limits. This examination was most consistent with optic nerve, oculomotor nerve, superior rectus muscle, and levator palpebrae muscle involvement. Given the patient's history and calvarial changes, metastasis was of most concern. However, given the location of the lesion and its radiographic well-circumscribed appearance, orbital meningioma was high on the differential diagnosis. A craniotomy with orbitotomy was planned with ophthalmological and neurosurgical collaboration.

A CT/positron emission tomography body scan was performed before the operation. This exhibited diffuse sclerotic bone, numerous tiny pulmonary nodules, hypermetabolic activity in the left orbital mass, and widespread osseous heterogeneous fluorodeoxyglucose uptake consistent with metastatic disease.

The patient was positioned supine, and the head was secured in skull pins with stereotactic navigation. She was given Ancef and 10 mg of dexamethasone. An extended pterional incision and craniotomy were created. A subfrontal, extradural approach was performed. With the operative microscope, the roof of the left orbit was freed. Using a medial, lateral, and anterior cut, a small orbitotomy was created using the Misonix BoneScalpel. The Kearson was used to complete the removal of the thin orbital rim. The periorbita was thick and adherent, making it difficult to dissect. Once the periorbita was carefully incised, the orbital contents were explored. The levator and the superior rectus complex were visualized but were also adherent to the tumor. The tumor was seen and dissected at the apex. Here, trochlear nerve and superior oblique muscle were identified and left undisturbed. The tumor invaded the levator palpebrae and superior rectus muscles and therefore was unresectable. Specimens were sent, and frozen section returned metastasis. The orbital roof created from the orbitotomy was replaced and secured with an absorbable plate and fibrin glue. The dura was closed with an only graft and reinforced with fibrin sealant. The bone flap was replaced with titanium plates and screws, and the wound was closed in layers of Vicryl and Monocryl. The patient tolerated the procedure well without complication.

The immediate postoperative examination was unchanged. She continued to have left upper eyelid ptosis and left-sided medial and supra gaze palsies. Dexamethasone was tapered, and she was discharged with therapy on postoperative Day 3. Surgical pathology of the left orbital mass revealed invasive ductal breast metastatic carcinoma. Immune profile studies were consistent with previous breast pathological examination. On follow-up visit at 1 month, her extraocular motility improved to full range, but she continued to have significant left ptosis. She received fractionated stereotactic radiotherapy to the remaining lesion with 25 Gray in 5 fractions and completed additional chemotherapy for the bone and lung metastases. Her tumor markers downtrended, and follow-up MRI revealed minimal improvement in the size of the left orbital metastasis (Fig. 2). At her 6-month follow-up visit, her ptosis had improved significantly, and the left extraocular muscles remained fully intact.

F2
FIG. 2.:
Postoperative MRI brain: (A) T1 postcontrast in coronal view (B). T2 in axial view (C). T1 postcontrast in axial view exhibiting a left orbital lesion diminished in size from 17 mm cephalocaudad 2–13 mm, and from 14 mm transversely to 10 mm. The tumor mass extends to the orbital apex as previously, but the crowding the orbital apex is diminished, and the optic nerve does not appear compressed as it did previously.

A combined neurosurgical/neuroophthalmological diagnostic and therapeutic collaboration through fronto-orbital approach with orbital osteotomy is often used for surgical work in the orbit (1). Because of the proximity to the optic nerve, the surgeon must plan for optimal exposure while minimizing functional deficits through diminishing direct and indirect contact with the optic nerve (1). The surgical anatomy of the orbital apex is delicate, complex, and essential to appreciate when decompressing the optic nerve. The roof of the optic canal is approximately 5–10 mm long and 4.5 mm wide with a roof thickness of only 1–3 mm. Removal of the roof is often performed with a high-speed burr drill leaving the underlying falciform process and optic nerve susceptible to direct mechanical injury from the rotating burr, thermal injury from heat extending from the drill, compression from the weight and force of the drill, and bone dust artifacts (2–4). The drill bit has a large working surface and can easily damage nearby neurovascular structures and capture surgical products such as sponges in the nearby field. This is seen even in the most experienced hands. In addition, aggressive drilling medially can result in violation of the ethmoid or sphenoid sinuses lending itself to cerebrospinal fluid leaks (1). Finally, drilling of the bone itself can lead to devascularization and bone necrosis (2).

Misonix BoneScalpel works through amplification of an electrical signal that is converted to ultrasonic, high-frequency back-and-forth motion of a blunt blade. It cuts through bone while leaving elastic soft tissues such as the dura mater and periorbita largely unaffected during incidental contact. The orbitotomy created by a bone scalpel allows for easier replacement of bone because of the minimal bone loss endured during the cutting of the bone. The bone flap is precisely configured and is easily returned to anatomical position which may lend itself to a decrease incidence of enophthalmos and pulsatile exophthalmos. Iacoangeli et al described use of the piezoelectric bone scalpel for removal of anterior cranial fossa meningiomas, orbital tumors, and sinonasal lesions with intracranial extension and found that although timing was prolonged, moderately follow-up showed faster and better ossification of the bone with good esthetic results (2). There are concerns regarding use of cavitron ultrasonic aspirator systems and subsequent cranial neuropathies. This brings up concerns around use of other ultrasonic tools. Acute damage is noted electrophysiologically through decreased amplitude of conducted nerve action potentials and increased latency of muscle action potentials. However, regeneration is evident by the second postoperative week (4,5).

Although the literature is limited with regards to use of the bone scalpel at the orbital apex, much of the safety literature around the use of the bone scalpel is present in the spine literature. There are multiple case series reporting decrease in operative blood loss (6–8), complication rates (6,9), and reduced operating time (6,9). In 2015, Onen et al described a case series of 46 patients who underwent decompressive surgery for cervical spondylotic myelopathy. This study found that patients who underwent an operation using the bone scalpel rather than the conventional high-speed drill had less operative blood loss, decreased length of surgery, decreased dural injury, and thereby a shorter length of stay (6). Nevertheless, Mathes et al followed up this study in 2018 with a blinded random control trial of 90 patients undergoing lumbar laminectomy, with either high-speed drill with automatic irrigation or ultrasonic bone-cutting knife (10). This study found a significant increase in thermal conduction and bone necrosis with a drill. This study did not note significant differences in neurological compromise or clinical outcomes between the 2 groups. As the research improves and the ultrasonic bone scalpel gains acceptance as a safe operative tool in the spine, surgeons are readily expanding its use, including skull base surgery (11).

In conclusion, the bone scalpel is a safe and effective tool for orbitotomy and intracranial approaches to the orbit and can decrease the incidence of mechanical and thermal injury of the optic nerve from large and potentially destructive drill bits. The authors found the use of the ultrasonic bone scalpel to be safe and efficient.

STATEMENT OF AUTHORSHIP

Category 1: a. Conception and design: L. Ross and R. Chu; b. Acquisition of data: L. Ross and S. Bose; c. Analysis and interpretation of data: L. Ross, R. Chu, and S. Bose. Category 2: a. Drafting the manuscript: L. Ross; b. Revising it for intellectual content: L. Ross, R. Chu, and S. Bose. Category 3: Final approval of the completed manuscript: L. Ross, R. Chu, and S. Bose.

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