Keywords
amaurosis - blindness, cortical - spine/surgery - scoliosis/complications
Introduction
Ophthalmologic complications after surgery are rare, with an incidence of approximately
1:125 thousand, and they are 75 times more frequent in patients undergoing cardiac
surgery.[1]
[2] In spinal surgery patients, the first description of this complication occurred
in 1950, and its estimated incidence ranges from 0.03 to 0.2%.[3] The main causes include external eye injury (EEI; corneal abrasion), cortical blindness
(CB), central retinal artery occlusion, and ischemic optic neuropathy (ION).[4] Many risk factors predispose to this complication, such as prolonged surgery, high
blood loss, prone position during the procedure, blood transfusion, arterial hypotension,
hydroelectrolytic imbalance, and cerebrospinal fluid loss.[5] Patient-related factors, such as atherosclerosis, obesity, diabetes mellitus, collagen
diseases, coagulopathies, systemic arterial hypertension, patent foramen ovale, peripheral
vascular disease, smoking, and alcohol and drug abuse deserve consideration.[6] Other independent risk factors include male gender, obesity, use of a Wilson frame
for patient positioning, longer surgical times, higher blood loss, and lower colloid-to-crystalloid
ratio in blood fluid administration. Modifying some of these factors may reduce the
risk of this complication, but its relatively low incidence, the ethical limitations
regarding randomized studies, and the lack of a current animal model limit the evidence
level.[7]
Report of three cases
In the 20-year survey period, from 2002 to 2022, 849 scoliosis correction surgeries
were performed at our institution. An analysis of the medical records revealed this
complication in the three following patients, who presented visual deficits in the
immediate postoperative period:
Case 1
We present the case of BDT, 13 years old, female, brown, weight of 36 Kg, body mass
index (BMI) of 18.4 Kg/m2, non-smoker, non-alcoholic, and non-user of illicit drugs. She had left-sided thoracic
scoliosis associated with the use of a chest tube at 3 months old due to pneumonia
that had been diagnosed late. Preoperatively, her Cobb angle was of 120°, and the
patient had a mild restrictive pulmonary disorder with no other known comorbidities
and an American Society of Anesthesiologists (ASA) I classification. She underwent
a T2-to-L3 thoracolumbar arthrodesis in 2 stages. The first surgical stage consisted
of curve instrumentation with pedicle screws, periapical osteotomies, and cranial
halo placement for intraoperative traction. The patient evolved well, and the 2nd
surgical stage, 14 days after the 1st, consisted of curve correction with rods and
an autologous graft. During surgery, general anesthesia was uneventful. The patient
received one bag of packed red blood cells. The intraoperative surgical bleeding was
of 600 mL, and wound drainage was of 400 mL. There was no hypotension, hypothermia,
neither were there other signs of hemodynamic instability during the perioperative
period. The total operative time was of 260 minutes. In the immediate postoperative
period of the second surgical procedure, the patient presented bilateral amaurosis
followed by difficult-to-control seizures and status epilepticus, requiring orotracheal
intubation. Seizure control occurred after the administration of an attack phenytoin
dose and phenobarbital. The team requested a contrast-enhanced computed tomography
(CT) scan and a magnetic resonance imaging (MRI) scan of the skull, a Doppler of the
carotid and vertebral arteries, and an electroencephalogram; all results were unremarkable.
The patient underwent evaluation by a multidisciplinary team, and the ophthalmologic
physical examination showed no retinal or pupillary alterations. After two days, the
patient spontaneously recovered her vision, with no impairment to her visual acuity.
The patient is under follow-up as an outpatient and remains stable.
Case 2
We reported the case of CRC, 19 years old, female, brown, weight of 34.4 Kg, BMI of
15.7 Kg/m2, without comorbidities, and ASA I. She had congenital thoracic scoliosis, with a
Cobb angle of 96° from T1 to T9 before surgery. The echocardiogram and ultrasound
(US) of the genitourinary system were unremarkable, and the MRI scan of the spine
showed no intraspinal alterations. Surgery consisted of a posterior vertebrectomy
of T6, osteotomy, and curve correction, followed by posterior arthrodesis from T1
to L3 using an autologous spinous process graft. The surgery occurred under neurophysiological
monitoring. The patient underwent general anesthesia. During the procedure, there
was significant hemodynamic instability due to excessive bleeding and a global reduction
in the neurophysiological signals measured. After strict control of the patient's
hemostasis and volume expansion, the team reversed and stabilized the condition. The
surgical bleeding was of 5 L, and the patient received 10 units of packed red blood
cells, 4 platelet bags, 2 plasma bags, 2 albumin bags, 1 g of methylprednisolone,
8.5 L of crystalloid, and 1 L of colloid. Clinical complications, including consumption
coagulopathy, bilateral pneumothorax, and pulmonary sepsis due to Klebsiella
sp. occurred postoperatively. The patient remained on mechanical ventilation for 18
days, with anisocoria identification on the 1st day. A multidisciplinary team monitored
the patient. Fundoscopy and CT of the skull were unremarkable. After the sedation
period, a new ophthalmological evaluation revealed amaurosis on the left side. The
patient was under follow-up for 2 years, showing partial visual field improvement,
but remained with visual loss-related restrictions.
Case 3
We present the case of LSSS, 14 years old, female, weight of 36 Kg, without comorbidities,
and ASA I. She had congenital scoliosis, with hemivertebra in L1 and a Cobb angle
of 68° (T12–L3) in the preoperative period. A preoperative transthoracic echocardiogram
showed mild mitral insufficiency, a urinary tract US revealed dilation of the right
renal pelvis, and an MRI scan of the spine showed no intraspinal changes. During surgery,
the surgeon performed L1 hemivertebra via a posterior approach, osteotomy, and curve
correction, followed by posterior arthrodesis from T11 to L3 with an autologous graft.
The surgery occurred under neurophysiological monitoring, and the final responses
were similar to the initial ones. The procedure required the transfusion of 1 unit
of packed red blood cells (packed cell volume: 23%). The intraoperative bleeding was
of approximately 500 mL, and the patient did not present hemodynamic instability or
neurophysiological sign alteration. The total operative time was of 270 minutes. Seven
hours after the end of the procedure, in the pediatric intensive care unit, the patient
presented a generalized tonic-clonic seizure lasting less than 5 minutes and received
anticonvulsant medication. Although she recovered consciousness in approximately 10 minutes,
she developed bilateral amaurosis, with complete deficit recovery 12 hours after its
onset. The team requested a CT scan, an MRI scan of the skull, and an electroencephalogram.
All tests, including the ophthalmological examination, were unremarkable ([Fig. 1]).
Fig. 1 Case 3: Congenital scoliosis treated with L1 hemivertebrectomy and T11–L3 posterior
arthrodesis. (A) Preoperative clinical images. (B) Preoperative radiographs. (C) Five-year follow-up clinical images. (D) Five-year follow-up radiographs.
Discussion
The following four conditions are the main causes of decreased visual acuity after
spinal surgery:
Ischemic Optic Neuropathy
Resulting from an imbalance between oxygen supply and demand in the optic nerve, which
damages the nerve fibers, ION can be anterior (AION) or posterior (PION). The impairment
is often very severe and bilateral due to irreparable optic nerve damage, regardless
of whether the injury occurred in the optic disc (AION) or the retrobulbar optic nerve
(PION).[8] The condition may be unilateral or bilateral, appearing immediately after surgery
or in a few days. To date, there is no proven beneficial treatment, and visual recovery
is usually poor. The posterior region is the area most commonly affected due to the
its peculiar vascularization. The posterior optic nerve receives blood from vessels
arising from the optic artery, which have poor autoregulation, making the nerve vulnerable
to anemia and hypotension.[9] Posterior ION presents as painless visual loss upon awakening from anesthesia. It
often does not progress, but recovery is poor, and no treatment has been proven effective.
In turn, prolonged prone positioning can cause postoperative facial or periorbital
edema, leading to indirect elevation of orbital venous pressures and contributing
to ischemia. Headrest use and constant head position monitoring during surgery have
been shown to reduce this complication[8] ([Fig. 2]).
Fig. 2 Main sites of abnormalities leading to postoperative visual loss and its different
causes. Abbreviations: AION, anterior ischemic optic neuropathy; PION, posterior ischemic optic neuropathy
(adapted from Williams et al., 199511).
Central Retinal Artery Occlusion
Central retinal artery occlusion results from decreased blood supply to the entire
retina.[7] It is associated with hypercoagulability states (causing embolism-related injury)
or external eyeball compression. This compression may occur, for instance, due to
the prone position during spinal surgeries, which increases intraocular pressure and
occludes the internal retinacular circulation. Retinal ischemia clinically manifests
as decreased pupillary reflex and a “cherry red” spot in the macula visible on fundoscopic
examination. Postoperative improvement is low, and there is no adequate treatment
for this complication.[8]
External Eye Injury
External eye injury presents as corneal ulceration or irritation resulting from direct
trauma related to the prone position, predisposing to infection and local inflammation.
The factors related to EEI include the prone position, Trendelenburg position, prolonged
operative time, and obesity. Positioning is the most controllable risk factor. Recommendations
to minimize the EEI risk include positioning the patient in ventral decubitus, adopting
10° to 15° of reverse Trendelenburg, ocular occlusion with a proper lubricant, and
facial support that releases the periocular region.[1]
[10]
Cortical Blindness
A rare clinical condition, CB is characterized by low visual acuity resulting from
injury to the retrogeniculate pathways or visual cortex.[1] It usually manifests upon awakening from anesthesia.[6] Stroke is its main cause, followed by embolic and other systemic conditions.[2]
[3] The main risk factors are systemic arterial hypertension, diabetes mellitus, hypercholesterolemia,
heart disease, atheromatous diseases of the neck vessels, smoking, use of oral contraceptives,
hormone replacement therapy, and stress.[1] The diagnosis relies on decreased visual acuity and visual field abnormalities associated
with infarction areas, mainly in the region of the posterior cerebral artery, confirmed
by CT or MRI scans.[7]
[8]
Visual changes after spinal surgery negatively impact the patient's quality of life;
an observational study[7] reported that 86% of patients undergoing spinal surgery in the prone position preferred
to receive information about the risk of visual loss. Recognizing and adequately managing
the risk factors and diagnosing complications early are essential to prescribe potentially-effective
therapies. Although hypotensive anesthesia prevents excessive blood loss during spinal
surgery, the cases herein reported have suggested that it may be a significant risk
factor for visual impairment; further research on the optimal blood pressure range
during surgery is warranted. Patients and physicians must assess and recognize the
benefits and risks of this strategy.[10] The proper prone positioning of the patient requires special attention[1]
[2] ([Fig. 3]). In the case series herein presented, bilateral amaurosis in the first and third
patients was part of the postoperative convulsive symptoms. The prognosis of CB depends
on the cause, severity, and duration of the triggering factor,[5] which explains why amaurosis is transient and patients recover quickly. Other combined
risk factors, such as hemodynamic instability, prolonged operative time, high blood
loss, and multiple transfusions of blood products and crystalloids indicate ischemia
of multifactorial etiology in the second patient. There is evidence that up to 94%
of the cases of optic nerve neuropathy occurred when anesthesia time exceeded 6 hours
and blood loss was higher than 1 L. A review study[11] indicated a strong association involving intraoperative arterial hypotension and
anemia with postspinal surgery amaurosis. The ASA, along with spinal surgeons and
neuro-ophthalmologists, developed a practical manual to prevent perioperative ophthalmological
complications in spinal surgery.[10]
[11]
[12]
[13]
[14]
[Chart 1] lists the main recommendations. However, it is worth noting that these recommendations
do not apply to CB.[10] Since there is no way to assure its prevention, it is critical to explain the risk
of visual deficit to patients who must undergo prolonged spinal surgeries in the prone
position, procedures with the expectation of substantial blood loss, or both; these
patients must sign the informed consent form.
Chart 1
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• Consider continuous blood pressure and central venous pressure monitoring.
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• Avoid direct pressure on the eyeball.
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• Positioning for high-risk patients includes placing the head at the same level (or
above) the rest of the body when possible. If feasible, the patient's head must be
in a neutral forward position (such as with no significant neck flexion, extension,
lateral flexion, or rotation).
|
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• Maintain blood pressure at higher levels in hypertensive patients to prevent end-organ
risk. Only use deliberate hypotension in high-risk patients when the anesthesiologist
and surgeon agree that it is essential.
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• Periodically monitor the levels of hemoglobin or packed cell volume during surgery.
The transfusion threshold that may decrease the risk of injury is unknown.
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• Use colloids and crystalloids to maintain intravascular volume in patients with
excessive blood loss.
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• Additional management may include optimization of the levels of hemoglobin or packed
cell volume, hemodynamic status, and arterial oxygenation.
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• Consider procedures in stages for high-risk patients.
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• Perform an ophthalmologic examination as soon as the patient becomes alert. If visual
loss is a possibility, request an urgent ophthalmologic consultation.
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Fig. 3 Prone positioning with attention to the correct head position and use of support.
One must pay attention to changes in position during the procedure in conjunction
with motor stimulation of neuromonitoring.
Visual loss after spinal surgery for scoliosis correction is a rare but severe and
sometimes irreversible complication. The surgical team must know about it to adopt
preventive measures and reduce its incidence.
