Malignant peripheral nerve sheath tumor in spine: Two case reports.

Dear Editor,

Malignant peripheral nerve sheath tumor (MPNST) is a rare variety of soft tissue sarcoma with an incidence of one per 1,00,000 population. They may arise spontaneously, although most of the cases are associated with neurofibromatosis type 1 (NF-1). They originate from a major or minor peripheral nerve branch or its sheath. The common sites of origin include the extremities and trunk, usually the sciatic nerve, brachial plexus, and sacral plexus. Only few cases of MPNST in the spine have been reported. The radiological features of MPNST in the spine are rarely reported in recent literature because of its low incidence. We describe the magnetic resonance image (MRI) findings of two histologically proven MPNSTs in the spine, operated in our institute.

The World Health Organization coined the term MPNST, replacing the previous confusing terminology like, malignant schwannoma, malignant neurilemmoma, and neurofibrosarcoma for tumors of neurogenic origin and similar biological behavior.[12] The preoperative diagnoses of MPNST on radiological findings are often difficult; even pathologists feel the difficulty in diagnosing these cases, because of its histological similarity to other spindle-cell sarcomas. The microscopic features of the spindle cell - with differentiation toward the element of the nerve sheath, varying degrees of mitosis, necrosis, and tumor calcification, with positive immunohistochemical staining for the S-100 protein, neuron specific enolase, and others like actin, cytokeratin, smooth muscle actins, desmin, and vimentin - are used to differentiate it from other spindle cell sarcomas.[3] Surgery is currently the mainstay of MPNST treatment.[4]

Case 1: A 75-year-old male presented to us with the history of a rapidly progressing swelling over the back, with a burning sensation over it and paraparesis. A hard, globular swelling was found over the back with a grade 0/5 power around all the joints in the lower limb and diminished sensation of all modalities below the L3 level.

An x-ray of the lumbosacral area revealed a height loss in the L3 vertebral body, with indistinctness of the left lateral border and non-visualization of the left pedicle [Figure 1a]. MRI of the lumbar spine revealed an expansive soft-tissue mass destroying most of the L3 vertebral body, pedicle, vertebral laminae, and spinous process of the neighboring side, with paraspinal extension and epidural cord compression. The mass was hypointense on T1 and hyperintense on T2 [Figure 1b and c]. An axial contrast-enhanced MRI scan showed an inhomogeneous enhanced lesion, with some non-enhancing areas of necrosis inside [Figure 1d].

Figure 1

(a) X-ray of the lumbosacral area showing height loss of the L3 vertebral body with indistinctness of the left lateral border and non-visualization of the left pedicle (b, c) MRI Spine: Sagittal and axial views showing an expansive soft tissue mass destroying most of the L3 vertebral body, pedicle, laminae, and spinous process of the neighboring side, with paraspinal extension and epidural cord compression. The mass is hyperintense on T2 (d) Axial contrast-enhanced MRI scan showing an inhomogeneous enhanced lesion and some non-enhancing areas of necrosis inside

Case 2: A 35-year-old female presented to us with a history of severe lower back pain, which was radiating to both the thighs, with paraparesis and bowel bladder involvement, for the last three months. An x-ray of the lumbosacral area revealed a height loss in the L5 vertebral body, with indistinctness of the left sacroiliac joint and non-visualization of the left pedicle [Figure 2a]. An MRI of the lumbar spine revealed an expansive soft-tissue mass destroying the L5 vertebral body, pedicle, vertebral laminae, and spinous process of the neighboring side, with paraspinal extension and epidural cord compression. The mass was hypointense on T1 and hyperintense on T2 [Figure 2b-d]. An axial contrast-enhanced MRI scan showed an inhomogeneous enhanced lesion and some non-enhancing areas of necrosis inside [Figure 2e].

Figure 2

(a) X-ray of the lumbosacral area showing height loss of the L5 vertebral body, with indistinctness of the left sacroiliac joint and non-visualization of the left pedicle (b, c, d) MRI Spine: Sagittal view showing an expansive soft-tissue mass, destroying most of the L5 vertebral body, pedicle, laminae, and spinous process of the neighboring side, with paraspinal extension and epidural cord compression. The mass is hypointense on T1, hyperintense on T2, and shows contrast enhancement (e) Axial contrast-enhanced MRI scan showing an inhomogeneous enhanced lesion and some non-enhancing areas of necrosis inside

Near total excision of the paraspinal and intraspinal components was achieved in both cases, followed by administration of local radiotherapy. At the six-month follow-up, case-1 was doing well, without signs of local or distant metastasis, whereas, case 2 expired because of lung metastasis and related complications.

Analyzing the radiological findings of our two cases, we found that it was possible to misdiagnose MPNST of the spine with a granulomatous lesion or a secondary.[5] In large lesions with vertebral destruction and paraspinal extension, it is difficult to comment on the origin of the tumor. MPNST should be kept as a differential diagnosis. Tissue diagnosis is mandatory to establish the correct diagnosis. The ‘target sign’ in an MRI scan, which is a feature of benign peripheral nerve sheath tumors, was not seen in our two cases.[6] This further supported that our two cases were not associated with NF-1. Despite aggressive treatment, many times, complete removal is not possible. Surgical tumor removal combined with postoperative high-dose radiation is recommended in such cases. Chemotherapy is usually reserved for patients with disseminated metastases or tumors that are unresectable at the time of diagnosis.