Lumbar spinal intraosseous schwannoma: a non-operative approach

Abstract

Intraosseous schwannomas are benign tumours composed of nerve sheath cells, most commonly affecting the mandible and sacrum. Such intraosseous schwannomas in the vertebra can result in spinal instability causing deformity, pain and even neurological compression. Vertebral involvement in the lumbar spine is extremely rare. A case of a schwannoma of the lumbar spine at the level of L3/L4 is presented. It resulted in progressive lower back pain and right lower limb radiculopathy. The clinical findings, radiological reports and histological diagnosis of this case, along with a review of the literature, are presented. The rationale for non-surgical management of this rare benign tumour is also explored.

Background

A rare case of a lumbar spinal intraosseous schwannoma at the level of L3/L4 is presented. A woman in her 50s was referred with a 3-year history of slowly progressive low back pain, radiating down the anterior aspect of the right thigh. An MRI of her lumbar spine demonstrated a large right-sided lesion at the L3/L4 vertebrae with involvement of the psoas muscle on that side. The lesion was biopsied on two occasions confirming no evidence of malignancy and discussed at numerous spinal tumour multidisciplinary meetings. Additional investigations included genetic evaluation for neurofibromatosis type 2 (NF2) and positron emission tomography (PET) scanning, both of which were negative. Given the morbidity associated with en bloc resection, minimal symptoms and the low likelihood of malignancy, a joint decision was made with the patient to treat this case non-operatively with serial imaging and close follow-up.

Case presentation

A woman in her 50s was referred to our institution with a 3-year history of lower back pain radiating to the anterior thigh on the right-hand side. The pain extended as far as the right knee. It was exacerbated by normal activities of daily living and resulted in subjective numbness, a feeling of pressure and loss of power in the right thigh. This pain was also particularly described at rest and was noted to wake the patient from sleep at times. On examination, the patient had intact sensation (2/2) to sharp and soft touch from L2 to S1 bilaterally. Power was 5/5 in all myotomes in the left lower extremity. Regarding the right lower limb, there was diminished power in the hip flexors (4/5), while knee extension, ankle dorsiflexion, long toe extension and plantar flexion were normal on examination.

MRI of the lumbar spine was obtained which demonstrated a large lesion on the right side arising from the exit foramen at L3/L4, clearly involving the vertebral body and extending into the psoas muscle on the same side (figure 1A, B). CT imaging the same month demonstrated a large lytic component to the involvement of the L3 vertebral body (figure 2). A CT-guided biopsy of the affected vertebral body confirmed a histological diagnosis of schwannoma. A PET-CT scan was undertaken to exclude the possibility of metastatic spread (figure 3A, B). The patient’s case was subsequently discussed at a spine multidisciplinary meeting, involving radiation oncologists, histopathologists, orthopaedic spine surgeons and neurosurgeons. The consensus opinion was that the lesion appeared atypical in nature by virtue of its intraosseous location and large size. The team also agreed that there was no instability present, given the imaging performed and the lack of significant neurology.

Figure 1.

STIR (Short Tau Inversion Recovery) sequence MRI showing a large lesion on the right-hand side arising from the exit foramen at the level of L3/L4: (A) sagittal view, (B) axial view.

Figure 2.

CT scan demonstrating a mass at the level of the L3 vertebral body with a large lytic component.

Figure 3.

Positron emission tomography-CT showing an isolated hypermetabolic mass lesion in the right paraspinal region at L3 with invasion of the L3 vertebral body and extension to the right L3/L4 neural foramen. No distal disease is evident. (A) coronal view, (B) sagittal view.

A repeat CT-guided biopsy was organised. This demonstrated fibroconnective tissue and skeletal muscle with a bland spindle cell proliferation and focal inflammation. No mitosis or necrosis was seen. The spindle cells were positive for S100 (figure 4) and negative for Melan A, CD34 and Desmin. Ki67 showed a low proliferation index in the spindle cells consistent with a schwannoma (figure 5). Genetic screening was then undertaken, excluding the presence of NF2.

Figure 4.

S100-positive tumour tissue. S100 is a marker of Schwann cells and melanocytes (magnification ×40).

Figure 5.

Tumour tissue stained for Mib1 (Ki67), a marker of cell proliferation. This shows a low proliferation index in this case, with very few cells staining (magnification ×200).

The patient was counselled regarding the options of non-operative versus operative management, with options including en bloc and intralesional resection. The risks associated with non-operative management included increase in tumour size with compression of adjacent neurological and vascular structures, and potential for malignant change. Operative risks outlined the potential profound loss of power in the lower extremities if the lumbar nerve roots were resected.

As the lesion was causing significant compression of the inferior vena cava (IVC), input was sought from the haematology service regarding the need for prophylactic anti-coagulation in the form of an IVC filter. It is well-known that persistent compression of the IVC can be associated with lower limb deep vein thrombosis. The patient in question had no personal or family history of thromboembolism. There were also no symptoms of venous congestion in the lower limbs such as oedema, erythema or other cutaneous signs of venous obstruction. Given the risks associated with anti-coagulant therapy, the haematology service felt that such therapy was only warranted where the risk of thrombosis was likely to be in excess of any risk of morbidity associated with major bleeding.

Outcome and follow-up

Given her minimal symptoms, the patient decided to opt for non-operative management comprising regular follow-up with serial clinical evaluation and MRI scanning at 6-month intervals. This is ongoing, and the patient is still doing well 2 years post-diagnosis.

Discussion

Schwannomas represent the most common benign tumour in peripheral nerves, commonly occurring alongside the vestibular branch of the cranial nerve.¹ They arise from Schwann cells, which produce myelin.² These tumours are made up of spindle cells and show a positive immunoreactivity for S100 protein.³

Intraosseous schwannomas are rare, accounting for just 0.2% of primary bone tumour.⁴ Spinal intraosseous schwannomas are rarer. The most common sites for intraosseous lesions are the mandible and the sacrum.²

A review of current literature (table 1) demonstrated 21 case reports (27 patients) presenting with spinal intraosseous schwannomas, with only 6 of these being described in the lumbar spine. Male patients outnumber female patients (male 16, female 11) with patient ages ranging between 22 and 75 years. The majority of cases presented were in patients in their 40s.^2–23

Table 1.

Review table of previous cases of intraosseous schwannoma

Paper	M/F	Age	Presenting symptom	Onset	Physical examination	Imaging	Biopsy	Treatment	Outcome
Xu et al4	M	50s	Neck pain	2 years	N/A	Osteolytic destruction of C7 vertebra MRI → space-occupying lesions in C7 vertebra and destruction of anterior cortex of the vertebra	Pathological examination confirmed diagnosis of schwannoma	Focal excision of the lesion, followed by C7 fusion using an iliac bone graft	NER (No evidence of recurrence) 1 year
Vasudevan and Kutty5	M	40s	Left-sided facial numbness, difficulty chewing and progressive difficulty walking due to spastic paraplegia	Numbness for 1 year, spastic paraplegia for 6/12	N/A	MRI and CT → heterogeneous intensity lesion in left infratemporal region and multiple small tumour masses in neck arising from cervical nerve roots MRI of spine → intradural schwannoma compressing the cord at thoracic level	Histology and immunohistochemistry confirmed schwannoma	Surgical removal of the spinal lesion, mandibular lesion and neck swellings	N/A (Not available)
Jia et al6	F	60s	Back pain	Several months	Loss of light tough sensation and thermal hyperalgesia in lower extremities and the lower limb muscle strength was 4/5	CT and MRI → 2× intraosseous tumours at the T7 and T8 levels and an intradural extramedullary tumour at T5–6 levels	Histopathology showed schwannomas	Surgical resection of intraosseous tumours at T7 and T8 levels and tumour at T5–6 was not found	Postop MRI showed in the extramedullary tumour had moved toT3 -T4 levels— eventually found and removed at T1–T2
Zaidman et al7	F	50s	Fluctuating diplopia and fatigue	1 year	Physical examination normal	CT → vertebral bony lesion with lytic features MRI → T1 hyperintense lesion located in T1 vertebral body, extending to right pedicle	Positive for S100 Histopathology showed a lesion composed of spindle cells	Anterior approach surgical resection	Postop CT and X-rays show complete resection of the lytic lesion
Silva et al8	M	20s	Bilateral lumbar pain, abdominal pain, nausea, fever and difficulty walking	24-hour history (previous episode of same 2/12 prior)	Inferior abdominal pain and lower back pain on percussion	X-ray → lesion next to left sacral wing PET/CT showed large osteolytic lesion with soft tissue component in left sacral wing	Bx → spindle cell neoplasm	Local complete excision of tumour via left foraminotomy L5–S1 and partial osteotomy of the post wall of sacrum	NER 2 years
Zhang et al2	M	70s	Right lumbocrural pain and gait disturbance with paraesthesia and right leg weakness	6/12	Impaired right leg motor function (grade 3/5) and diminished feeling on right side caudally from lumbar L4 dermatome	MRI → mass with lesions in L4 vertebral body and spinal canal compressing the lumbar spinal cord	Overexpression of S100 protein	Total laminectomy and facetectomy of L3–5 with tumour excision	NER 2 years
Zhang et al2	F	50s	Gait disturbance and bilateral lower limb paraesthesia	4/12	Numbness in both legs without obvious weakness	MRI → mass appeared to originate from posterior element of T9 and extended into spinal canal and paravertebral areas, extruding the spinal cord	Pathology confirmed schwannoma	Surgical resection of tumour	NER 4 years
Song et al9	M	40s	Intermittent lower back pain radiating to right leg	3 years	Localised pain on percussion of lumbar spine Range of lumbar motion was decreased Straight leg test was limited	CT → irregular mass at L5 involving right pedicle and posterior protrusion compressing thecal sac	Positive for S100 proteins	L5 laminectomy with resection of tumour Intervertebral fusion L4–S1	NER 1 year
Patnaik et al10	M	70s	Progressive bilateral lower limb weakness	3/12	Grade 0 power bilaterally	MRI → large mass in paraspinal and retrospinal region L3 vertebral body was collapsed	Spindle cells but also nuclei which were buckled and comma shaped with prominent nucleoli suggestive of malignancy	L3 laminectomy with tumour resection	Diagnosed as a malignant tumour Expected poor outcome
Peng et al11	M	40s	Previous resected (2 years prior) intraosseous schwannoma in C spine—p/w dizziness and mild weakness in right upper limb	6/12	N/A	CT → expansile, osteolytic and invasive lesion in C3 vertebral body The right pedicle, laminar and spinal process were destroyed	N/A	Removal of posterior C2–C3 tumour and implantation of autograft and calcium phosphonate posteriorly	Two years postop showed tumour relapse and hyperintense signal mass in C3 vertebral body expanded to the spinal canal and impinged spinal cord
Youn et al12	M	60s	Progressive lower back pain; right hip and thigh pain, tingling and numbness in right foot	5 years	N/A	CT → mass with marginal sclerosis located at right side of L2 vertebrae MRI showed sclerotic margin involving right posterior lamina, right pedicle and articular process of L2	Histopathology confirmed schwannoma	Surgical excision of tumour with posterior fusion of L1–L3	NER 1 year
Mizutani et al13	F	40s	Bilateral upper limb paraesthesia	1/12	N/A	MRI → mass lesion in C4 vertebral body CT showed a bony defect in CR body but cortex was preserved	Positive for S100 protein	Surgical resection of tumour	Paraesthesia persisted at 17 months postop, but no signs of recurrence
Kojima et al14	M	60s	Back pain and progressive lower limb weakness	Several months	Power 4/5 bilaterally Knee and ankle jerk reflexes exaggerated	CT → large lytic lesion occupying the posterior column of T9 with erosion of lamina and spinous process MRI → spinal cord compression by the lesion	Spindle cells	Surgical resection and reconstruction with pedicle screws	NER at 2 years
Pongsthorn et al15	F	50s	Left leg pain	2/12	N/A	Intraosseous type	N/A	Posterior enucleation	NER at 12 years
Pongsthorn et al15	M	30s	Right gluteal pain, leg and foot numbness	23 years	Bilateral leg hypoalgesia No motor weakness	CT → extensive bony destruction MRI tumour arising from right S1 root	N/A	Combined subtotal	NER at 11 years Erectile dysfunction and motor weakness postop
Pongsthorn et al15	F	50s	Right leg pain, calf numbness	12 years	N/A	Dumb-bell type, size 12 cm	N/A	Combined, partial resection	Recurrence after 7 years Second surgery completed, no recurrence after 15 years

Bx, biopsy; CR, combined resection; N/A, not available; NER, no evidence of recurrence; PET, positron emission tomography.

Indications to consider operative management include the presence of spinal instability,²⁴ curative resection and local symptom control. This patient’s case did not demonstrate any radiological evidence of instability and her symptoms were minimal. Pain and paraesthesia are the most commonly reported symptoms on presentation.¹⁹ One case in the literature was diagnosed incidentally on imaging.¹⁹

Schwannomas are generally encapsulated. They are non-responsive to radiotherapy with surgical resection being the principal treatment of choice.²⁵ Treatment of intraosseous schwannoma is generally performed by curettage or en bloc resection followed by bone grafting.^{3 25} Recurrence is rare but may be associated with incomplete resection.^{3 25} All reported cases in the literature underwent surgical resection of the tumour,^{2–23 25} and while the length of follow-up varies, the vast majority of the cases were recurrence free. Only two cases had recurrence and required further surgery.^{11 15}

An important factor to consider when contemplating surgical resection is the presence of mutations in the NF2 gene, which encodes for Merlin.^{26 27} Merlin is a tumour-suppressor protein and loss of function through mutations or deletions in NF2 causes NF2. This is a multiple tumour-forming disease of the nervous system, with the potential for malignant transformation,^{26 27} mandating en bloc resection.²⁵

While schwannomas are typically benign tumours, there are documented cases of previously benign schwannomas recurring with malignant potential.¹¹ One malignant primary case of intraosseous schwannoma has been described.¹⁰ No factors associated with increased risk of malignant change have been identified to date in the absence of NF2 expression. However, reports of malignant recurrences highlight the importance of long-term follow-up for patients who undergo surgical resection.¹¹ Patients should be monitored with both physical examinations and regular imaging.

The risk of postoperative risk of deep vein thrombosis is well established in spinal surgery.²⁸ The risk of thromboembolic disease is also noted with IVC compression.²⁹ However, to date, the authors could not find any literature that establishes or discusses the potential risk of thrombosis from IVC compression caused by spinal tumour. It is therefore imperative to involve haematology colleagues in ongoing consultation to establish the risks versus benefits of anti-coagulation in this rare patient cohort.

Given the significant postoperative morbidity associated with surgical resection, non-operative management of intraosseous schwannomas is a valid option. This may be applicable to patients with minimal symptoms who have a confirmed histological diagnosis of schwannoma and who are NF2 negative. The vast majority of intraosseous schwannomas in the literature have been treated with surgical resection,^2–23 with almost all of these lesions demonstrating benign histology. En bloc surgical intervention in this patient’s case would result in resection of the right L3 nerve root and potentially other elements of the lumbosacral plexus resulting in marked weakness in the right lower limb. This would be a devastating complication in an otherwise well, independent woman. The consensus opinion from our expert group is to manage this patient non-operatively, with serial MRI scans and neurological assessments.

Learning points.

• Intraosseous spinal schwannomas are an extremely rare type of tumour.

• Most cases are benign; however, there are documented cases of malignant transformation.

• Complete surgical resection is the most common treatment, though this can result in very significant postoperative long-term disability.

• We describe a non-operative approach in an attempt to preserve patient quality of life.

• Regular patient imaging is paramount to a non-operative care strategy.

Ethics statements

Patient consent for publication

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