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Sacral schwannoma


Introduction

Intradural extramedullary (IDEM) tumors are tumors of the neuro-axis that grow within the confines of the dura mater but are extrinsic to the spinal cord itself. Epidemiological studies have estimated the incidence of IDEM tumors to be approximately 0.74 per 100,000 persons. Although a variety of tumor types may be found within this compartment, the most common are benign tumors such as meningiomas or schwannomas. Meningiomas are benign tumors arising from arachnoid cap cells of the dura; thus, they are typically attached to the dura with a broad base. Their histology is identical to their intracranial counterpart. Schwannomas arise from the dorsal or ventral nerve root, with the dorsal roots being more common. These tumors are hypothesized to originate in the Obersteiner-Redlich zone, which is the transition point between oligodendrocytes of the central nervous system and Schwann cells of the peripheral nervous system. Schwannomas typically arise from a single-nerve fascicle and displace the surrounding roots, causing compression and leading to pain, sensory loss, and weakness. Although these tumors arise from the nerve fascicle itself, this involved fascicle rarely contains functional tissue and thus can typically be ligated without clinical sequelae.

The most common tumors to be found in the sacrum are metastases or a primary tumor such as chordoma, but other tumor types can also be found originating in the sacral region. Schwannomas of the sacrum are rare and account for approximately 1% to 5% of all spinal schwannomas. There have been limited reports discussing the surgical management of these cases. In this chapter, we discuss the management of a patient with a sacral tumor and discuss the anatomical associations to be considered when approaching this region.

Example case

  • Chief complaint: urinary retention, buttock pain

  • History of present illness: This is a 43-year-old female with right-sided buttock pain and urinary retention for 1 year. She has no pain in her legs. She reports subjective decrease in sensation in her genitals. Magnetic resonance imaging (MRI) of the sacrum raises concern for a nerve sheath tumor ( Fig. 50.1 ).

    Fig. 50.1, Preoperative T2 magnetic resonance imaging (MRI) of the sacrum. (A) Mid sagittal and (B) coronal images demonstrating a sacral tumor emanating from the right S2 nerve root. There is enlargement of the S2 foramen as the tumor is seen traveling along the nerve. Red arrow highlights the tumor.

  • Medications: gabapentin, antidepressants

  • Allergies: no known drug allergies

  • Past medical history: none

  • Past surgical history: hysterectomy, C-section

  • Family history: no history of malignancies

  • Social history: none

  • Physical examination: awake, alert, and oriented to person, place, and time; cranial nerves II–XII intact; bilateral deltoids/triceps/biceps 5/5; interossei 5/5; iliopsoas/knee flexion/knee extension/dorsi, and plantar flexion 5/5

  • Reflexes: 2+ in bilateral biceps/triceps/brachioradialis with negative Hoffman; 2+ in bilateral patella/ankle and no clonus or Babinski; sensation intact to light touch

  • Laboratories: all within normal limits

  • Jorge Eduardo Guzman Prenk, MD

  • Neurosurgery

  • Pontificia Universidad Javeriana

  • Bogota, Colombia

  • Daniel J. Hoh, MD

  • Neurosurgery

  • University of Florida

  • Gainesville, Florida, United States

  • Adrian Casey, MD

  • Neurosurgery

  • National Hospital for Neurology and Neurosurgery

  • Queen Square, Holborn, London, United Kingdom

  • Jean-Paul Wolinsky, MD

  • Neurosurgery

  • Northwestern University

  • Chicago, Illinois, United States

Preoperative
Additional tests requested None

  • CT lumbar spine

  • Urodynamic testing

  • Possible CT-guided biopsy

  • MRI brain and complete spine

  • CT chest/abdomen/pelvis

  • Urodynamic testing

  • Neurophysiology assessment

  • PET if diagnosis uncertain

Urodynamic testing
Surgical approach selected S1-2 laminectomy for resection of tumor S1-2 laminectomy for resection of tumor S2 laminectomy for resection of tumor S2-4 laminectomy for resection of tumor
Goal of surgery Diagnosis, decompression of nerve roots Diagnosis, gross total resection Diagnosis, maximal safe resection, prevent further deterioration Decompression of nerve roots, resection of lesion
Perioperative
Positioning Prone Prone Pone Prone
Surgical equipment

  • Fluoroscopy

  • IOM (EMG sphincter/bladder)

  • Surgical microscope

  • Fluoroscopy

  • Surgical microscope

  • Fluoroscopy

  • IOM (EMG sphincter/bladder)

  • Surgical microscope

  • Ultrasonic bone cutter

  • IOM (EMG sphincter/bladder)

  • Fluoroscopy

Medications None Ketorolac 48 hours after surgery +/– steroids None
Anatomical considerations Sacral nerve roots namely sciatic and pudendal

  • Sacral nerve roots

  • SI joints

Sacral nerve roots, dura S2-S4 sacral nerve roots
Complications feared with approach chosen Nerve root injury, CSF leak S2 nerve root injury, CSF leak Residual lesion, CSF leak, nerve root injury causing urinary incontinence Nerve root injury
Intraoperative
Anesthesia General General General General
Exposure S1-3 S1-2 S2 S2-4
Levels decompressed S1-2 S1-2 S2 S2-4
Levels fused None None None None
Surgical narrative Position prone, medial incision from S1-3, subperiosteal dissection of muscles, transverse angled retractors locked in place, mainly right S2 laminectomy with high-speed drill, dissect nerve root from distal to proximal, monopolar stimulation for EMG or relay on CMAP recording, dissect and remove tumor, layered closure Position prone, vertical midline incision over sacrum, fluoroscopy to confirm S1-2 level, drill and rongeurs to perform right-sided S1-2 laminectomy, identify right S1 nerve root within canal and exiting out S1-2 foramen, open dura overlying nerve root sleeve under microscope, follow tumor proximally to nerve root axilla to evaluate for intrathecal extension, internally debulk tumor and follow distally through S1-2 foramen, may need to unroof foramen to full extent, dissection and Position prone, x-ray level check, midline incision at S2, subperiosteal muscle dissection to expose laminae, x-ray level check, S2 laminectomy using high-speed drill or ultrasonic bone cutter under microscopic visualization, dissection of presumed nerve sheath tumor, identify lesion and delimitation of edges, excision of lesion +/– nerve root sacrifice, send tissue for histology, dural closure with clips, dura Position prone, IOM, localization x-ray, midline incision from S2-S4, subperiosteal exposure of S2-4 spinous process and lamina, localization x-ray, S2-4 laminectomies, dissection and identification of bilateral S2-4 nerve roots and tumor, isolate likely S4 nerve root, identify nerve proximal and distal to the tumor, ligate proximal aspect of S4 nerve root below thecal sac with 2-0 silk suture and then cut, cut S4 nerve root distal to tumor, deliver
peel tumor capsule off of remaining fascicles, meticulous dural closure with fibrin glue, multilayer closure, horizontal mattress sutures in skin, immediate mobilization after surgery repair with glue, layered closure, flat for 48 hours if CSF encountered entire tumor in one piece, hemostasis with gentle irrigation, layered closure with attention to lumbosacral and Scarpa’s fascia with subfascial drain tunneled below lumbosacral fascia in rostral direction away from incision and carried out through separate stage incision, skin closure with glue
Complication avoidance Right hemilaminectomy, follow course of entire nerve from distal to proximal, monopolar stimulation and CMAP to identify nerve roots Right hemilaminectomy, follow course of entire nerve, assess for intradural tumor, internally debulk tumor before peeling tumor from fascicles, fibrin glue, immediate mobilization after surgery Follow course of entire nerve, identify beginning and termination, determine whether nerve needs to be sacrificed, flat for 48 hours if CSF encountered Isolate nerve root where tumor is coming from, ligate and cut proximal nerve root first, en bloc tumor removal
Postoperative
Admission Floor Floor Floor Floor
Postoperative complications feared Nerve root injury, CSF leak, epidural hematoma, infection Nerve root palsy, pain, CSF leak, urinary retention, paralytic ileus Nerve root injury causing incontinence or sexual dysfunction, CSF leak, infection Urinary retention, persistent urinary tract infections, wound infection, CSF leak
Anticipated length of stay 2 days 2–4 days 5–7 days 1–3 days
Follow-up testing

  • MRI 4 months after surgery

  • Possible genetics evalaution pending histology

MRI 3–4 months after surgery, then annually for 5 years MRI 3 months, yearly for 2 years MRI 6 weeks after surgery if en bloc achieved (<48 hours if subtotal resection), 6 months, 12 months, 24 months, 36 months after surgery
Bracing None None None None
Follow-up visits 2 weeks, 4 months after surgery 3 weeks, 6 weeks, 3–4 months after surgery 6 weeks, 3 months, yearly for 2 years after surgery 2 weeks, 6 weeks, 3 months, 6 months, 12 months, then annually after surgery
CMAP , Compound muscle action potential; CSF , cerebrospinal fluid; CT , computed tomography; EMG , electromyography; IOM , intraoperative monitoring; MRI , magnetic resonance imaging; PET , positron emission tomography; SSEP , somatosensory evoked potentials.

Differential diagnosis

  • ▪

    Nerve sheath tumor

  • ▪

    Metastasis

  • ▪

    Chordoma

  • ▪

    Tarlov cyst

  • ▪

    Other primary bone tumor

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