Sixteen patients with 15 foraminal benign PNSTs and a foraminal MPNST underwent surgery at SUMC between 1993 and 2006. Of 16 patients, four with benign PNSTs and one with a MPNST underwent CyberKnife RS in addition to surgery.
Tumor locations and nerve root involvement
Tumor locations included seven cervical, two thoracic and six lumbosacral PNSTs; the MPNST was in the cervico-thoracic region. One MPNST and eight PNSTs were located on the left and seven PNSTs on the right.
Classification and imaging characteristics
Eleven foraminal schwannomas were classified using Asazuma et al.’s system (Fig. ) [3
]. Of four cervical schwannomas which involved a single IF (Cases 1, 11–12 and 15), TFs were not involved: two exhibited epidural thecal sac compression (type IIa with cord compression, IF stage 1, TF stage 1 and 2 were without thecal sac compression (type IIa, IF stage 1, TF stage 1). Another cervical tumor (Case 9) abutted the left vertebral artery and extended into the prevertebral soft tissues (type IIb with cord compression, IF stage 1, TF stage 2). One intra- and extradural cervical tumor (Case 5) expanded from the foramen into the lateral soft tissues (type IIIb with cord compression, IF and TF stage 1). A type VI, IF stage 2, TF stage 1 thoracic foraminal schwannoma (Case 8) expanded two adjacent foramina and caused erosion of the superior pedicle and transverse process (Fig. ). Three lumbar schwannomas (Cases 3, 10 and 13) were each located in a single IF and were type IIa, IF stage 1; Case 13 remained the same type at presentation for CyberKnife RS. Case 2 was located in a single IF with right cord compression and thus was a type IIa with cord compression.
Schwannomas exhibited an intermediate T1-weighted (T1) signal intensity (SI) on MRI and were of intermediate-or-hyperintense SI on T2-weighting (T2). Gadolinium-uptake, common to schwannomas, was homogeneous in nine and heterogeneous in two. On computerized tomographic (CT) scanning, schwannomas are iso- or hypodense and may show bony erosion.
Intraforaminal neurofibromas were categorized using the Asazuma et al. classification [3
]. Of neurofibromas, one involved the left C5–C6 foramen (Case 16) and resulted in mild thecal sac compression and vertebral artery displacement (type IIa with cord compression, IF stage 1, TF stage 1) and had the same pattern at presentation at surgery and CyberKnife RS. Two other lumbar dumbbell tumors (Cases 4 and 7) each had retroperitoneal and paraspinal extensions, respectively (type IIc, IF stage 1). Another neurofibroma (Case 6) resulted in bony remodeling of the vertebral bodies (type VI, IF stage 1).
Neurofibromas were found to have a low or intermediate SI on T1 MRI. On T2, signal hyperintensity or a hyperintense rim with an intermediate SI focus (target sign) was seen; gadolinium-enhancement occurred in all neurofibromas in this series. On CT scan, neurofibromas are hypodense and tend to have a dumbbell shape; there is often bony erosion.
The pre-operative MPNST MRI (Case 14) revealed a uniformly enhancing, partially cystic left foraminal C7–T1 tumor extending into the adjacent paraspinal soft tissues (type IIb, IF stage 1, TF stage 1). At the second surgery, the tumor was intradural (type IIIa): CyberKnife RS was next used for residual enhanced soft tissues bordering the spinal canal at C6–T1.
On MRI, MPNSTs have been shown to be inhomogeneous with patchy contrast enhancement, which, per Mautner et al. [29
] corresponds to areas of necrosis and hemorrhage. Malignant PNSTs characteristically exhibit decreased T1 SI, which is markedly increased on T2 MRI (Table ). The MPNST on CT is hypodense and ill-defined with contrast enhancement and it enhances marginally.
The MPNST in the present series had the atypical presentation of, T1-homogeneity and uniform-enhancement on post-contrast T1. This tumor also had a central non-enhancing cystic component, which extended from the lateral margin of the foramen into the paraspinal soft tissues.
Presenting symptoms and findings are included in Table . Patients with schwannomas and neurofibromas were evaluated individually for presenting symptoms and findings. Of eight patients with schwannomas who underwent a single open surgery, seven presented with radiculopathic symptoms with intact (2), radiculopathic (3) or myelopathic (2) findings; the eighth patient had been experiencing radiculomyelopathic symptoms with myelopathic findings at the time of presentation. Of three patients with schwannomas who had CyberKnife RS in addition to their original surgery, two patients each had one operation presenting in each instance with radiculopathic symptoms and findings. CyberKnife RS followed at the time of recurrence and one patient had radiculopathic symptoms and findings and the other, radiculomyelopathic complaints and myelopathic findings. Another patient undergoing additional CyberKnife ablation initially had surgery with radiculopathic symptoms and findings. This surgery was followed by CyberKnife RS and at that time the patient presented with radiculopathic symptoms and radiculomyelopathic findings. Pre-operatively at the second surgery, this patient presented with radiculomyelopathic symptoms and findings.
Of three patients with neurofibromas, each underwent a single operation for tumor resection. Pre-operatively, one was asymptomatic and intact, and two had radiculopathic complaints with an intact examination in one and radiculomyelopathic findings in the other. Another patient with a neurofibroma had two operations for tumor-removal followed by CyberKnife RS. Prior to each of the two operations, the patient experienced radiculopathic complaints and findings and pre-CyberKnife RS, the symptom and finding presentations were radiculomyelopathic.
The patient with a foraminal MPNST (Case 14) presented with radiculopathic symptoms and findings at the time of the first operation. At both the subsequent re-operation and at CyberKnife RS, the patient also presented with radiculopathic symptoms, but had progressed to radiculomyelopathic findings.
Potential associated predisposing factors
Neurofibromatosis type I
Of four patients with benign foraminal neurofibromas, three had associated NF1 (Table ). No patients had NF2, nor schwannomatosis.
Associated radiation history
One patient with a left C7–T1 foraminal MPNST had a history of Hodgkin’s disease 14 years earlier, which had been treated with radiation therapy to the mantel field. The radiation consisted of 36–44 Gy to the neck, chest, and under-arm lymph nodes. The disease had been in remission, until the foraminal MPNST developed in the prior radiation field.
Operative reports documented approaches for removal of 15 foraminal PNSTs and one MPNST (Table ). The procedures were analyzed with reference to Asazuma’s tumor categorization and are presented in order of number and increasing complexity.
Surgical approaches for foraminal tumors
Two patients with foraminal IIa, IF1, TF1 schwannomas, one at C4–C5 (Case 12), which was followed by CyberKnife RS and the other at C3–C4 (Case 1), underwent a midline posterior laminectomy with partial facetectomy and a posterior cervical triangle approach, respectively. A similar cervical schwannoma (Case 11) without cord compression, was removed using a laminectomy with total facetectomy and fusion. Case 16 presented with cord compression and underwent a laminectomy and partial facetectomy. A recurrence was treated with CyberKnife RS and the patient remained stable for 72 months. The tumor increased in volume and the patient underwent a re-do laminectomy, facetectomy and fusion. For IIb, IF1, TF1 (Case 9) and IIIb, IF1, TF1 (Case 5) schwannomas both with cord compression, a laminectomy with partial facetectomy and hemilaminectomy with partial facetectomy and partial pedicle removal were used, respectively.
A right posterior mediastinal tumor, 9.5 × 10.5 cm type VI with cord compression (Case 8), was an IF 2 thoracic tumor with retromediastinal and spinal extensions and was removed in two stages (Fig. ). Three IIa, IF1 lumbar schwannomas (Cases 10, 3 and 13) underwent (1) an L4 laminotomy, (2) a partial L2, L4 and complete L3 laminectomy and (3) a laminectomy with partial facetectomy and partial pedicle removal, followed at recurrence by CyberKnife RS, respectively. Case 2, a IIa, IF1 lumbar schwannoma with cord compression was removed via a laminectomy, total facetectomy and fusion.
Fig. 2 An 87-year-old female (Case 8) presented initially with shortness of breath (SOB), back and right lower extremity (LE) pain and bilateral LE weakness. Five years earlier, a 2.0 × 3.0 cm right posterior mediastinal mass (more ...)
An anterior supraclavicular approach for Case 16 to resect a C5–C6 tumor (IIa with cord compression, IF1, TF2) was used twice followed by CyberKnife RS. A lateral extracavitary approach (LECA) was used for a type VI, IF1 thoracic tumor (Case 6) and an L3–L5 IIc, IF1 (Case 7) was removed via a lateral paraspinal approach. A retroperitoneal approach was carried out in Case 4, a type IIc, IF1.
The foraminal C7-T1 MPNST (type IIb, IF stage 1, TF stage 1) underwent a gross total resection (GTR) via a C7 hemilaminectomy and total facetectomy with fusion. A recurrence was removed via a partial C6, T1, total C7 laminectomy and total facetectomy with fusion then CyberKnife RS.
Nerve root preservation versus transection
Information regarding preservation or resection of the involved nerve root was available for nine patients with benign foraminal schwannomas and four with neurofibromas. The dorsal nerve root from which the tumor originated was preserved in each of six schwannomas and transected in two. In another schwannoma, both the dorsal and ventral nerve roots were involved and both were transected after intraoperative ventral root stimulation revealed a lack of motor function; the ventral root in the latter case was described as being dysplastic. Of four neurofibromas, two had the dorsal nerve roots preserved. Another two neurofibromas had their dorsal nerve roots transected to enable tumor removal.
Intraoperative electrophysiological monitoring
Somatosensory-evoked potentials (SSEPs) and motor evoked potentials (MEPs) were monitored during surgery. A handheld monopolar stimulation electrode was used to elicit evoked electromyographic (EMG) responses to identify and to trace the course of nerves in relation to the tumor.
In the case of motor nerve roots, all fascicles involved by tumor which failed to evoke motor impulses were removed. Conversely, all motor fibers that evoke either muscle contraction or EMG response were left intact.
Of eight patients with schwannomas, who underwent a single operation, symptoms improved in seven (88%) and one worsened. Two patients undergoing a single surgery followed by CyberKnife RS experienced symptom improvement in all instances. Another patient had surgery followed by CyberKnife RS then further surgery and had symptom improvement. She then became worse and remained unchanged.
Three patients with neurofibromas underwent a single operation: one patient without complaints remained unchanged and the other two patients had improvement of symptoms. The fourth patient with a neurofibroma who underwent two operations followed by CyberKnife RS experienced either no change or improvement in symptoms after all procedures.
The patient with an MPNST had an improvement in symptoms postoperatively after the initial surgery. The symptoms recurred and after the second surgery followed by CyberKnife RS, the patient expired from tumor spread.
Neurological examination outcomes
Eight patients with schwannomas who underwent a single operation either remained intact (2) or improved (6). Two patients with schwannomas undergoing a single surgery followed by CyberKnife RS had improvement in their examinations after both procedures. One patient with a schwannoma who had surgery, improved then underwent CyberKnife RS and worsened after 48 months. After further surgery, the patient became remained unchanged.
Three patients with neurofibromas underwent a single operation: two patients who were intact preoperatively, remained unchanged, another had improvement of findings. Another patient underwent two operations followed by CyberKnife RS and experienced improvement, no change then improvement in findings.
The patient with an MPNST had an improvement in his examination after the first operation. The presentation again worsened and after the second surgery followed by CyberKnife RS, he expired as described above.