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  5. FP644 : Surgical Outcome of Optic Canal Decompression in Direct and Indirect Traumatic Optic Neuropathy

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Dr. Kasturi Bhattacharjee, B07299, Dr. Deepika Kapoor, Dr. Harsha Bhattacharjee

Kasturi Bhattacharjee, Harsha Bhattacharjee, Deepika Kapoor

Traumatic Optic Neuropathy (TON) is an injury to the optic nerve subsequent to a head or Orbitoadnexal trauma wherein road traffic accident being an important cause. The incidence of TON after closed head injury ranges from 0.5-5.0%1.

Manifestations of TON include a mild diminution to a complete loss of vision. Since, road traffic accident is common in younger age groups, visual loss following TON poses a greater challenge for the economically productive age group. Other clinical features include visual field defect, color vision defect and relative afferent pupillary defect. TON can be due to direct or indirect injury to the optic nerve. Indirect form is the most common form of TON, which occurs following acceleration or deceleration forces due to blunt trauma to the head, especially the forehead region.3 Blunt force trauma transmits a shock wave to the optic canal leading haemorrhage, vasospasm, edema, and necrosis, which in turn leads to compartmental syndrome by swelling of the optic nerve in the canal.4 Assessment of the surrounding soft tissue and bony injuries of the optic canal may be useful in determining the injury of the optic nerve and it can be used as a prognosis predictor of TON.5 On the other hand, direct traumatic optic neuropathy results from direct trauma to the optic nerve from sharp objects, missiles and bony fragments leading to anatomical damage to the optic nerve. The degree of severity of the injury does not always predict or correlate with the amount of visual loss.

Treatment options include observation, intravenous steroids, surgical decompression of optic canal and a combination of both.  The management remains controversial, as there is no convincing studies which clearly show the efficacy of medical or surgical treatments. The present study has been undertaken to establish an effective standard of care in direct and indirect TON cases.

Aim:  To analyse the visual outcome following navigation guided external transcaruncular optic canal decompression in Traumatic optic neuropathy.

Materials and Method: This was a hospital based, prospective interventional case series. The study was approved  by  the  Institutional  Ethics  Committee  and  followed  the  principles  outlined  in  the  Declaration  of  Helsinki on human study. All consecutive patients of >18 years of age presenting with TON without brain trauma were included in the study. Inclusion criteria were, H/O injury within last 3 months, age >18 years, vision < Finger Counting close to face (FCCF) and could  not  be  explained  by  other  causes with  a  relative  afferent  pupillary  defect,  .

Thorough history was recorded in relation to details of trauma, primary treatment before referral, H/O Intravenous methyl prednisolone (IVMP), pattern of visual loss and associated ocular injury. Complete ocular examination including vision, pupil, anterior segment, fundus and disc, Intra Ocular Pressure was done. Diagnosis was made based on clinical findings along with radio imaging (CT/MRI), VEP and OCT RNFL. Pre operatively High-resolution computed tomography (HRCT) scan of the head and the orbit (contiguous slices of 1mm thickness and 1mm slice interval, FOV upto 250) was done in all cases along with Magnetic Resonance angiography (MRA) to rule out any other pathologies such as low flow carotid cavernous fistula.

All patients received IVMP 1 gram daily for 3 days preoperatively and  then  patients  whose  Visual Acuity did not show any improvement  after  intravenous  treatment  were recommended to minimally invasive transcaruncular external optic canal decompression (TCEOCD). Enrolled  surgery  cases  were  divided  into  direct TON   group  and  Indirect TON   group  based on the radiological findings of any fractured bony segment/ hyperostotic bone or haematoma compressing the optic nerve.

The surgery was performed under general anesthesia. All operation performed by the same single surgeon. Pre-operative CT scans of orbit and optic canal were obtained as per navigational guidelines. The data was then uploaded on the Stealth Station’s S7 workstation and 3-D model was build using the software. The software provides a scope for further planning of the surgery by deciding the entry point and a target are (here medial wall of the optic canal), creating a colour coded model of the specific anatomical entity (e.g. optic nerve, optic canal, blood vessels, extraocular muscles etc.).  The specific registration process is to be followed before staring the surgery for Navigation system. The surgery was performed under continuous monitoring using the Navigation probe to locate the specified anatomical landmarks.  The optic canal was approached via medial transcaruncular incision and further dissection was carried out to access the medial wall of the orbit. The posterior ethmoid bone was located and further upward and medial direction dissection  was done to approach the optic canal via the sphenoid sinus. Once the target area was reached and confirmed using the Navigation stylet, the medial bony wall canal was punched out with a 1mm Kerrison punch, and the bone fragment impinging the optic nerve was removed. In case of pre-existing bony fractures of optic canal, fractured segments were removed whenever found. The conjcutival incision was closed with 6-0 polyglactin interrupted sutures. Postoperatively, all patients received  intravenous injection erythropoietin 6000 IU daily for 3days, oral citicoline 500mg tablets 8 hourly daily for 3 months  & oral and topical antibiotics for one week. Patients were followed up at day 1, day 7, 1month, 3  months , 6 months , then every one yearly after  surgery.  A patient’s visual acuity (VA) was considered to have improved if an improvement was from no-light-perception to light perception or further better from the preoperative recorded vision.

Results:

21 patients including 19 male, and 2 female patients with TON unresponsive to oral steroids were enrolled into the study. Only four patients presented within 7 days of injury, ten patients presented from 7 days to 1 month and rest seven patients within 1 month to 3 months range. Out of 21 patients, 11 had direct TON with bony impingement while 10 had indirect TON. Of the 11 patients with direct TON , 9 had the  optic  canal  fracture and  another  2  were detected  during  the  surgery.  6 of Direct TON patient and 7 of Indirect TON cases had haemorrhage within the posterior ethmoid and/or sphenoid sinus. During  the  surgery,  4  patients  developed  cerebrospinal fluid  leakage during decompression of the optic canal and all were managed with orbital fat tamponade  during  surgery  and advised   strict  bed  rest  in  30  degrees  of  head-up  and  feet-down  position.

Visual acuity was ≤ FCCF but > PL +ve in 5 patients and rest 16 patients denied light perception (PL) at presentation. At 6th month, 5 cases PL +ve, 7 had VA≤ 20/100 and 5 had VA≥ 20/60. 4 remained PL -ve with lag time of >4 weeks from injury. Colour vision was recovered in 5 cases. 15 patients had improvement in VEP P100 amplitude.19 patients showed improvement in RNFL thickness at 6 months post-operative. 12 out of 16 patients with NPL had improvement in vision to PL and better.

Discussion: 

The pathophysiology of direct or indirect TON is multifactorial. Indirect injury often from acceleration or deceleration forces due to blunt trauma to the head or globe resulting in haemorrhage, vasospasm, intra neural contusion, edema, and necrosis, leads to swelling up of the optic nerve in the canal and to compartmental syndrome.5 The use of the high or mega dose of corticosteroids for TON patients in National Acute Spinal Cord Injury Study II  (NASCIS II) has shown improvement in acute spinal cord injury patients but later Corticosteroid Randomization After Significant Head (CRASH)  injury study revealed that this regime increased the relative risk of death in patients with head injury. The International Optic Nerve Trauma Study  (IONTS) concluded that neither corticosteroids nor OCD is the standard of care for TON patients and it should be treated on individual basis. Surgical decompression of the optic nerve has been debatable since long, however recently, benefits of surgical OCD in both direct and indirect TON has been reported2. Pre-surgical planning and intraoperative localisation under navigation helped to prevent accidental optic nerve injury in our cases.  The management of TON remains controversial, as there is no convincing studies, which clearly show the efficacy of medical or surgical treatments. The recent introduction of Stereotactic Navigation technology has opened a new door of possibility in ophthalmic surgeries. This technology has a potential to provide better localization and precision to aid in the optic canal decompression surgery, and possibly a better visual outcome. 2

The navigation system provides the projection mode and the “look ahead” programme mode  that helps the surgeon to see what lies further ahead on the screen. This helps to avoid any inadvertent damage to important structures. The intraoperative use of stylet provide the exact position and can confirm radiological validity of the particular structure. This external medial transcaruncular approach with Navigation guidance provides better surgical access and better intraoperative guidance.

The commonly recognised indications of OCD surgery are radiological evidence of OCF, impingement of optic nerve by fracture fragment, intraneural edema and an optic nerve sheath hematoma.6 However, recent studies have found that OCD has role in both direct and indirect type of TON. In our case series, 17 out of 21 (80.95%) cases had visual recovery following optic canal decompression with improvement in VEP parameters in 15 cases. Wentao Yan et al5 reported the visual improvement was 78.4% for patients with OCF and 87.6% for patients without OCF in a large retrospective comparative case series. They also demonstrated that in 20.9% patients, OCF were not detected pre-operatively by HRCT, which were noted intraoperatively during endoscopic trans-ethmoidal OCD.

In the present study, 75% patients with PL negative vision reported an improvement of VA after TCOCD. 61.90%  of  late  presented  patients  had  improved  V A  after OCD,  which  reminds  us  that  we should never give up TON patients with NLP vision or how late they present for treatment.

Medial transcaruncular approach for optic canal decompression in TON patients who are unresponsive to steroids provides easier and direct access to the optic canal, with good results and can be considered a standard treatment alternative for such patients. Thus, timely decompression of optic canal with systemic neuroprotective drugs offers to be an effective treatment modality for TON.

References:

  1. Carta A, Ferrigno L, Salvo M, et al. Visual prognosis after indirect traumatic optic neuropathy. J Neurol Neurosurg Psychiatry 2003;74(2):246-48.
  2. Ali M, Naik M, Girish C, et al. Interactive navigation-guided ophthalmic plastic surgery: assessment of optical versus electromagnetic modes and role of dynamic reference frame location using navigation-enabled human skulls. Clin Ophthalmol 2016;10:2383-90.
  3. Lee KF, Muhd Nor NI, Yaakub A, et al. Traumatic optic neuropathy: a review of 24 patients. Int J Ophthalmol 2010;3(2):175-178
  4. Chou PI, Sadun AA, Chen YC, et al. Clinical experiences in the management of traumatic optic neuropathy. Neuro-ophthalmology 1996;16:325-336
  5. Yan W, Chen Y, Qian Z, et al. Incidence of optic canal fracture in the traumatic optic neuropathy and its effect on the visual outcome. Br J Ophthalmol 2017;101:261–67.
  6. Kumaran AM, Sundar G, Chye LT. Traumatic Optic Neuropathy: A Review. Craniomaxillofac Trauma Reconstr. 2015;8(1):31-41.

 

 

 

 

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