Introduction

In patients diagnosed with adolescent idiopathic scoliosis (AIS), there is a demonstrated neurologic complication rate of 0.69% [1,2,3]. Causes of neurologic complications after scoliosis surgery can be the result of spinal cord ischemia, cord compression, cord stretch, and/or direct trauma to the spinal cord [2, 4]. A delayed neurologic deficit is very rare, with only a few case reports on record to date. A study performed with surgeons in the Scoliosis Research Society identified the incidence of delayed postoperative neurologic deficit as 0.01%, or 1 out of every 9910 cases [5]. The current authors report the case of a 12-year-old girl with severe AIS of 125° who experienced the onset of complete lower extremity paraplegia (American Spinal Injury Association [ASIA] Impairment Scale B) 36 h after stage one of a planned two-staged posterior spinal fusion (PSF). As a case report, institutional review board approval was not required.

Case presentation

A 12-year-old girl presented with severe progressive AIS measuring 125˚ and complaints of shortness of breath with activity (Fig. 1). Preoperative magnetic resonance imaging (MRI) revealed a small (2-mm) syrinx and Type 3 spinal cord deformation at the apex of the deformity [6] (Fig. 2). The patient had a normal neurologic examination with no upper motor neuron findings.

Fig. 1: Preoperative standing radiographs.
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Preoperative posteroanterior (PA) (A) and lateral (B) erect radiograph demonstrating a 125° right thoracolumbar scoliosis.

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Fig. 2: T2 weighted magnetic resonance imaging axial cut centered at T8.
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The spinal cord (arrow) is draped over the concave left T8 pedicle causing cord deformation and loss of circumferential CSF at the apex of the curve.

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Due to the severity and stiffness of the deformity (major coronal curve corrected < 20% on preoperative bending/traction radiographs), a one- or two-stage PSF was planned. Stage one would involve placement of pedicle screw instrumentation, posterior column osteotomies (PCO), and possible placement of rods and completion of the procedure pending flexibility after the PCOs. If the curve was felt to be too rigid even after PCOs, the initial procedure would be concluded and a halo would be placed on the patient for perioperative halo gravity traction (HGT). HGT would be utilized for 4 weeks after the initial procedure to further reduce the severity of the deformity. Finally, the patient would be scheduled to undergo an apical vertebral column resection (VCR) and completion of the PSF as a second stage procedure.

The initial procedure was performed with total intravenous anesthesia (TIVA) and intraoperative neuromonitoring (IONM) with transcutaneous motor evoked potentials (tcMEPs) and somatosensory evoked potentials (SSEPs).

A transient drop in TcMEPs occurred during one of the apical posterior column osteotomies. TcMEP signals returned immediately with elevation of the mean arterial pressure (MAP) to >85 mmHg. After completion of all PCOs from T4-L1, it was felt that the deformity was sufficiently flexible to attempt completion of the PSF without the need for a second stage VCR. During rod placement for curve correction, TcMEPs diminished in lower extremities for a second time but immediately returned to normal when the rod was removed. It was elected to abort the case at this point with plans to schedule a second stage. The patient awoke with normal a neurologic exam and was transferred to the pediatric intensive care unit to maintain MAPs ≥ 85 mmHg for 48 h to ensure adequate spinal cord perfusion (Fig. 3).

Fig. 3: Intraoperative radiograph after the primary procedure.
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Immediate postoperative anteroposterior (AP) supine radiograph after initial instrumentation procedure.

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On postoperative day (POD) #1, the patient exhibited normal strength and sensation in her bilateral lower extremities. She was maintained on bedrest as she required dopamine to maintain her MAP > 85 mmHg. On the morning of POD #2, 36 h after stage 1 surgery, the patient awoke with no motor and limited bilateral lower extremity sensation (ASIA Impairment Scale B). Critical review of the vital signs revealed that the patient’s MAP had fallen to 70–75 mmHg for a period of 2 h overnight. The patient’s MAP was emergently elevated to >90 mmHg with no significant improvement in the neurologic examination. Emergent CT myelogram was obtained, and concern for potential epidural hematoma at T7–8 was noted as there was a loss of dye at the apex of the deformity (Fig. 4).

Fig. 4: Myelogram image (right) with evidence of absence of contrast at the apex of the deformity.
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Axial CT myelogram images of T7 (top left) and T8 (bottom left) demonstrate no evidence of medial pedicle screw breach and absence of contrast at the apex of the deformity.

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The patient was taken emergently to the operating room for a T5–T10 laminectomy. No epidural hematoma was identified, but it was noted that the spinal cord was tightly draped over the concave apical pedicles. The concave pedicles of T7 and T8 were then resected. The cord immediately changed in caliber from a flat ribbon to a tubular structure with dural pulsations subsequently noted. The cord appeared adequately decompressed after this maneuver, and there was a slight improvement noted in TcMEPs. Over the next 72 h, MAPs remained at >85 mmHg. A postoperative wakeup test revealed improved sensation in the lower extremities and volitional left great toe flexion/extension. The patient continued to improve to 3/5 motor strength globally in the left lower extremity and right toe flexion/extension within several hours of the decompression. Within 48 h, the left lower extremity had returned to full strength, while the right lower extremity strength and sensation recovered fully after five days. One week after the neurological exam normalized, the patient was returned to the operating room for completion of the PSF with a modest correction and no further resections or osteotomies. Prepositioning TcMEPs/SSEPs were normal, albeit at an increased voltage from the initial procedure (600 V vs. 300 V, respectively) and remained unchanged throughout the procedure. The patient’s neurologic exam remained normal. Five years post-op, the patient is an active college student with full function and no activity limitations (Fig. 5).

Fig. 5: Most recent followup radiographs.
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Five-year postoperative PA (A) and lateral (B) erect radiographs following T2-L4 posterior spinal fusion.

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Discussion

There are few cases in the literature reporting the delayed onset of a neurologic deficit following operative treatment of scoliosis. The different etiologies cited for a delayed onset neurologic deficit have been reported to include presence of a hematoma [7, 8], decreased spinal cord perfusion [9], excessive distraction of the spine [10], spinal cord impingement secondary to bone graft migration [11], and tumor growth [12]. Our case contributes to the current literature about this rare, delayed neurologic complication in spine deformity surgery with recommendation of apical pedicle resection.

The use of spinal cord monitoring has been highly recommended during procedures for the detection and prevention of neurologic injury [7, 13]. While this can be performed using the “wake-up test,” the use of somatosensory cortical evoked potentials has its advantages due to its ability to continuously monitor the patient and avoid any risks involved in waking the patient intraoperatively [13]. IONM makes it possible to identify neural injury within a period that allows for surgical or anesthetic intervention as a means to reverse any potential damage [14]. A potential neurologic deficit when using SSEPs is a 50% reduction in amplitude and/or 10% increase in the latency [15]. The incorporation of tcMEPs allows for monitoring of the corticospinal tract, allowing full monitoring of the sensory and motor tracts [13]. If changes to neurologic activity are detected during the procedure, it is important to attempt to identify the timing and causative factors for the change. This can involve optimizing cord perfusion by raising the MAP and/or reversing previous surgical steps (removal of a corrective rod and/or problematic pedicle screw) [16]. An intraoperative checklist has been developed to guide the surgical team to systematically respond to IONM alerts [17]. If these maneuvers result in normalization of IONM signals, it has been demonstrated that the procedure can safely continue. However, if patient optimization and reversal of potentially inciting factors fail to achieve an improvement in IONM signals, it is recommended that the procedure be aborted. IONM is obviously not available postoperatively to acutely monitor spinal cord function, and the surgeon is entirely reliant on the patient’s examination and verbalization of any new complaints (paresthesias, weakness, etc.).

Induced hypotension has been implemented as a means to produce ideal operative conditions and reduced blood loss during surgery. However, spinal cord ischemia can arise from excessive and prolonged hypotension, mechanical compression, and/or spinal cord distraction. Due to the vascular anatomy of the spine, the thoracic spinal cord receives less blood supply than the cervical or lumbosacral regions of the spine. The artery of Adamkiewicz supplies approximately 68% of the thoracolumbar spine. A porcine study evaluating overdistraction with Harrington rods demonstrated that at least 35% of baseline blood flow is required to maintain SSEP and MEP signals, and paraplegia was associated with blood flow decrease to below 12% of baseline. The same animal study found that gross motor function returned after release of distraction if MEPs were lost for less than three minutes, while motor function was not recoverable if distraction was maintained for longer than three minutes. Thus, the faster time to intervention or reversal of factors contributing to cord ischemia has been shown to reduce the chances of a permanent neurologic deficit.

Prolonged optimization of MAPs after the time of injury has been recommended to maintain adequate spinal cord perfusion in the setting of a neurologic deficit or injury. Vale et al. [18] demonstrated that patients with an acute neurologic deficit or injury could potentially improve when MAPs are maintained above 85 mmHg. Unfortunately, given the paucity of data on delayed neurologic deficits, there are no existing guidelines for treatment of this relatively rare phenomenon. In the case of our patient, the MAP unintentionally dropped below 85 mmHg to 70–75 mmHg for 2 h in the early morning of POD #2 while the patient was sleeping, likely potentiating the neurologic decline. The patient’s examination failed to significantly improve despite elevating the MAP well above 85 mmHg, indicating continued spinal cord ischemia or irritation possibly from mechanical compression. A CT myelogram was obtained to localize the exact region and cause of the spinal compression. This demonstrated a loss of contrast dye at the apex of the deformity, which was postulated to be the result of an epidural hematoma. Emergent exploration/laminectomy revealed no evidence of a hematoma, but the spinal cord was acutely draped over the T7 and T8 concave pedicles. After resection of these two concave pedicles, the caliber of the spinal cord returned to a more normal, tubular structure, and dural pulsations also resumed. A recent classification of the location and character of the spinal cord on preoperative MRI found that patients were 28 times more likely to have a drop in IONM signals when the spinal cord deforms against the apical pedicles and there is a lack of CSF between the cord and vertebrae. This was the case with our patient, which would therefore classify her spinal cord as a Type 3, placing her at a higher risk for a neurologic event.

The finding of a small syrinx around the apex of a severe, angular deformity is not uncommon, as this likely represents a potential disruption in the normal flow of cerebrospinal fluid in this area where the spinal cord is kinked around the deformity. It is unclear if this represents a true subclinical spinal cord injury but does predispose the patient to a higher risk of neurologic injury with spinal surgery according to Sielatycki et al. as stated above [6].

The authors feel this case report is useful for several reasons. Strictly maintaining adequate MAP and cord perfusion postoperatively is paramount if a significant loss of IONM signal is encountered during scoliosis surgery. Our patient experienced transient hypotension to 70–75 mmHg 36 h postoperatively, which was enough to trigger a complete loss of lower extremity motor function. Secondly, it was assumed that the loss of CT myelogram dye was due to an epidural hematoma, which was not found. The angular deformity caused the spinal cord to acutely kink over the concave pedicles, which caused a mechanical cord compression. Emergent concave apical pedicle resection caused an immediate improvement in IONM and eventual return of normal function after 48 h. The new MRI classification of spinal cord location/deformation can help risk stratify patients prior to surgery. The surgeon should always consider pediculectomy for spinal cord decompression in the setting of any changes with IONM during spinal deformity surgery. A pedicle resection was not performed during Stage 1 in this case as the intraoperative signals had returned to normal upon removal of curve correction. If this had not occurred, a pedicle resection would have been performed immediately to decompress the spinal cord. One could also consider a prophylactic resection of the apical concave pedicles in severe deformities. However, this is a potentially more invasive procedure, which would also preclude placement of pedicle fixation at the apex of the deformity and thus could impair curve correction. Therefore, the authors would not recommend that this prophylactic procedure be routinely performed for all severe deformities, but it should be considered if any neurologic changes occur.

Finally, the authors did not place a temporary rod along the pedicle covering the apex of the deformity at the index procedure; it was felt that this temporary rod would inhibit gradual deformity correction with planned halo gravity traction. However, at the time of the emergent return to surgery, it was evident that the deformity had become considerably more flexible after the PCOs performed at the initial procedure. It is possible that the curve increased across the apex of the deformity after the initial procedure, causing further cord compression across the apical pedicles. Placement of an in-situ titanium temporary stabilizing rod across the apex of the deformity may have restricted any motion experienced across the apex of the deformity and, potentially, minimized further cord compression.

A neurologic deficit during and/or following spinal deformity surgery is a devastating complication. Much interest and research has been directed towards the management of IONM changes to minimize the potential for permanent deficits. However, the rarity of a delayed postoperative neurologic deficit limits our ability to adequately study and potentially respond to this rare phenomenon, which is limited to several case reports. Currently, a multicenter collaboration is underway to critically evaluate as many of these rare cases as possible to identify causative factors and develop appropriate treatment recommendations.