Simultaneous L1–2 Bulged Disc and Mobile Spinal Schwannoma Causing Cauda Equina Syndrome: A Rare Case Report

Introduction

Herniated lumbar disc is one of the most frequent symptomatic spinal pathologies, which can cause low back pain and radiculopathy [1,2]. Schwannomas, which are benign tumors that originate from Schwann cells of the myeline sheath, can cause similar symptoms [3,4]. They, however, can be locally aggressive, and although rare, have been reported to cause serious neurological deficits, including cauda equina syndrome (CES), a neurosurgical emergency characterized by compression of nerves at the lower end of the spinal cord, resulting in symptoms such as lower back pain, leg weakness, bladder and bowel dysfunction, and saddle anesthesia [1,5,6]. Migratory spinal tumors are rare with schwannomas are the most common type to move, as other common primary intraspinal neoplasms, such as meningiomas and ependymomas, are fixed in their position [5]. Symptomatic mobile spinal schwannomas have rarely been reported, and reports of simultaneous presentation of these tumors with disc disease at the same spinal segment are even scarcer. Cases of cauda equina syndrome resulting from intraspinal schwannomas, specifically with spontaneous improvement, are also rarely reported. This report describes a unique case of a 62-year-old man presenting with cauda equina syndrome caused by a bulged L1–2 intervertebral disc combined with a mobile spinal schwannoma.

Case Report

A 62-year-old man with diabetes presented with 2 weeks of intermittent bilateral leg pain radiating from his lower back, which abated at night. The patient experienced an acute episode of lower extremity weakness and difficult urination. In neurological examination, distal leg muscle power was documented as bilateral weakness of dorsiflexion 3/5 and plan-tar flexion 4/5. Non-contrast magnetic resonance imaging (MRI) was performed in the Emergency Department, revealing a well-defined intraspinal tumor rostral and adjacent to the L1–2 disc (Figure 1A). Six hours later, he was admitted to the hospital and a second MRI was conducted, with contrast, which demonstrated the mass caudal and adjacent to the L1–2 disc (Figure 1B). Meanwhile, his symptoms had resolved and the examination of his lower extremities revealed a stocking distribution sensory loss, with no apparent motor weakness. Due to persistent episodes of pain, the patient was scheduled for surgical resection of the tumor. Our surgical technique involved a spinous process-sparing unilateral approach to the spine to preserve the interspinous ligament. Through a complete laminectomy of L1, a wide access to the canal was achieved. We used standard microdissection techniques, using the operative microscope for tumor dissection from the nerve root and neuromonitoring with electromyogram recording of the lower extremities and sphincter. Under the operative microscope, the tumor was lobulated and yellowish in color; it did not follow the root into the foramen (Figure 1C).

The mass was adherent to a rootlet that stimulated the left S1 myotome and was dissected free from the tumor mass. The primary fascicle leading into and out of the tumor did not stimulate. Intraoperative ultrasound revealed a 1.5-cm mobile mass rostral and adjacent to the L1–2 disc within the spinal canal (Figure 1D). With ultrasound-induced cerebrospinal fluid pulsations, the bulged disc served as a barrier to prevent caudal migration of the mass. Pathological assessment of the tumor confirmed the diagnosis of schwannoma. The patient’s symptoms had resolved postoperatively, and he was symptom-free at his 3-month follow-up visit.

Discussion

We present this case to highlight that some spinal pathologies can present simultaneously with atypical and potentially misleading clinical manifestations. The challenges associated with diagnosis and surgical management should be considered. Furthermore, surgeons need to take necessary steps to perform surgery with the available intraoperative imaging tools, to avoid wrong-level spinal surgery and its dire consequences for both patient and surgeon. Patients who conservatively treat for intervertebral disc herniation and concomitant mobile spinal tumors should be taught to be informed about the alarming symptoms of CES to mitigate the devastating neurological sequelae resulting from delayed treatment.

In the present case, while the L1–2 disc herniation could have resulted in bilateral leg and low back pain, the ball-valve effect could be the most likely explanation for the CES underlying mechanism. Cerebrospinal fluid flow obstruction caused by the mobile intraspinal schwannoma in the supine position at the level of disc bulge might have led to acute neural compression and subsequent neurological symptoms, such as CES.

Some reports have previously represented mobile spinal tumors and indicated the increased risk associated with surgical resection of these tumors, due to the unpredictable displacement of these lesions up to the time of resection [7–11]. Marin-Sanabria et al reported a patient with mobile spinal schwannoma who underwent L1 laminectomy and durotomy, based on the tumor location on preoperative MRI. Despite the expansion of the incision between T12 and L1, the tumor could not be identified [12]. Postoperative MRI revealed 2.2-cm caudal migration of the tumor.

Intraoperative myelography, ultrasonography, and MRI have been used to determine the mobility of schwannoma [9,13]. Notwithstanding, each method has its own set of issues. Intraoperative ultrasound and MRI may not be available in many centers. Lack of technical expertise and knowledge of interpreting sono-anatomy and the risk of moving intubated patients to an MRI suite are other issues [14,15]. Moreover, the contrast medium infusion and postural changes during myelography can cause the tumor to move. This, however, can be advantageous in some cases. Kasama et al successfully used intraoperative ascending myelography to relocate a caudally displaced schwannoma back to the durotomy site to avoid additional laminectomy [9].

To the best of our knowledge, there have been 6 case reports describing coexisting spinal schwannoma and lumbar disc herniation; however, none of them were mobile schwannomas and caused CES simultaneously, which is described in the present case [2,16–20]. Baek et al reported a 71-year-old woman with lower extremity and low back pain, which exacerbated acutely. Her MRI scans revealed the diagnosis of simultaneous disc herniation and intradural schwannoma [16]. A relatively similar case was also reported by Fujii et al, in which a patient presented with anterior thigh and low back pain. The patient’s symptoms were aggravated while he was treating conservatively. MRI scans showed a herniated L2–3 disc, with an intrathecal tumor at the same level [18]. Liu et al also reported a case of a patient with a L2–3 herniated disc, who developed symptoms of CES. MRI scans demonstrated a concomitant spinal schwannoma at the same spinal level [17]. Surgical resection of the mentioned pathologies helped the patients be free of symptoms postoperatively.

Given that intervertebral disc herniation is a common cause of low back pain, these studies emphasized that the differential diagnosis for exacerbation of symptoms in a patient with lumbar disc herniation being treated conservatively can include a concomitant intraspinal mass. This is even more important in a patient who has a mobile-type spinal tumor, since it has potential to result in spinal stenosis and subsequent severe neurological symptoms, such as CES, as described in the present case.

To perform the surgical resection of the tumor as precisely as possible, it is important to have adequate visualization while applying an appropriate surgical approach and micro-dissection techniques, as we did in the present case. Our experience with this unique case of a mobile schwannoma that changed its location reminds operating surgeons to be aware of the potential challenges regarding tumor localization. Tools to assist during surgery include intraoperative ultrasound, MRI, and myelography. Patients with simultaneous mobile schwannoma can present with the ball-valve type cauda equina syndrome. To avoid irreversible neurological complications, patients with these conditions should be given comprehensive information on alarming signs and the necessity of emergency referral and treatment.

Conclusions

The coexistence of a mobile intraspinal schwannoma and herniated lumbar disc is a rare case that can result in permanent catastrophic neurological deficits. We would like to remind surgeons that rare conditions as described in this case, including mobile spinal schwannoma, simultaneous presentation of mobile spinal schwannoma and intervertebral disc herniation at the same spinal segment, cauda equina syndrome as a presentation of spinal schwannoma, and spontaneous improvement of cauda equina syndrome, can manifest simultaneously with atypical and potentially misleading clinical presentations. Surgeons need to consider using additional diagnostic measures, performing surgery with the available intraoperative imaging methods, such as MRI, myelography, or ultrasonography, to precisely localize pathologies. They need to use an appropriate surgical approach and microdissection techniques to precisely dissect the tumor from surrounding tissues and lower the surgical complications. Discussing alarming symptoms with patients, to mitigate the potential for devastating neurological sequelae resulting from wrong-level surgery and delayed treatment, is of paramount importance.