st gadolinium MR sequence through the L3-4 level on postoperative day #1 demonstrates a small focus of enhancing tissue at the left neural foramen suggestive for mild tumor residual (arrow); (B) Sagittal T1 post gadolinium MR sequence through the left L3-4 foramen postoperative day #1 shows similar enhancing focus likely representing mild residual disease (arrow); (C) Axial T2 MR sequence through L3-4 six weeks after the operation demonstrates mild increase in T2 hyperintense material at the operative site (arrow), portions of which likely represent postoperative fluid; (D) Sagittal T1 post-gadolinium MR sequence through the left L3-4 foramen six weeks after the operation demonstrates mildly more prominent tissue enhancement suspicious for residual/recurrent disease (arrow).

Figure 3. Histolopathology. (A) Smear preparation showing epithelioid tumor cells with eosinophilic to bubbly cytoplasm (arrows) embedded in an amorphous mucoid matrix. Nuclear atypia was mild to moderate. H & E. 40×; (B) Formalin fixed paraffin embedded sections showing epithelioid tumor cells in a mucoid matrix. H & E. 20×; (C) Cytokeratin AE1/AE3 was present in virtually all cells. Cytokeratin AE1/3. 20×; (D) Tumor cells were also positive for S100. 20×.

soft tissue, including lung parenchyma [6-8] . A summary of radiological characteristics of tumors included in the differential diagnosis is highlighted in Table 1.

3.1. Schwannomas and Neurofibromas

Schwannomas have been known to cause several bony changes, including pedicle erosion, neural foraminal widening, and vertebral body scalloping. They may be associated with hemorrhage, cysts, or fatty degeneration. MR imaging often demonstrates a well defined, solitary lesion with T2 hyperintensity and homogeneous enhancement. Surgical excision is considered curative (except with schwannomas in neurofibromatosis), however, structural changes caused by tumor growth may result in spinal instability following excision.

Neurofibromas can have similar imaging characteristics to schwannomas, although neurofibromas are often multiple, typically do not show hemorrhage, cysts, or fatty change. Neurofibromas also more often show a “target” sign on MRI in which there is peripheral enhancement and central hypoenhancement. Multinodular, often infiltrative lesions are termed plexiform neurofibromas and are associated with neurofibromatosis. The vast majority of spinal nerve root tumors in patients with NF-1 are neurofibromas, although both neurofibromas and schwannomas may occur in the absence of NF-1. Calcification is not commonly associated with neurofibromas. Surgical excision is considered more difficult as neurofibromas typically have greater fascicular involvement and tend to be invested within the nerve body. Solitary lesions of the spine occur in the ratio of 3:1 in favor of schwannomas.

3.2. Metastases

Metastastic tumors comprise the vast majority of extra-axial tumors, with the largest part being osteolytic metastases. Most metastases are extradural, while less than 5% are intradural and intramedullary [9]. Lymphoma, lung, breast, and prostate cancer represent the most common subset of osteolytic lesions, though approximately 10% of all patients with cancer will have spinal epidural metastases [1]. Patient’s history of cancer will help to direct diagnosis. Radiographically, these lesions may differ based on their respective cellular origin. Typically metastases are T1 hypointense, T2 hyperintense, with enhancement, although with an increasing sclerotic component there may be decreased T2 hyperintensity and enhancement. Treatment is palliative in nature, consisting of either surgery alone or surgery plus radiation therapy and many are also treated with radiation alone.

3.3. Chondrosarcomas

Chondrosarcomas are associated with bony destruction and extension into nearby soft tissues. CT or plain film imaging may best detect chondroid calcification, often seen in the soft tissue component of the mass, and is the radiographic hallmark of this entity. Chondrosarcomas are uncommonly seen in the spine, but when present are often thoracic in location. They can involve the posterior elements, vertebral corpus, or both. Wide surgical resection is advised, with post-operative radiation if full resection cannot be accomplished [10].

3.4. Giant Cell Tumors

Giant cell tumors (GCTs) are uncommonly seen in the spine, with sacral lesions accounting for the largest subset of spinal lesions. Radiographically, GCTs are characterized as lytic, expansile lesions with eccentric bone destruction on plain films and CT imaging, exhibiting “a soap bubble effect”. These masses are often very heterogeneous on both CT and MR imaging and frequently demonstrate cystic change, internal hemorrhage, and fluid-fluid levels. Giant cell tumors are vascular masses and show enhancement on post-contrast imaging. Marginal excision with or without pre-operative embolization is advocated, though complete sacrectomy may be too extreme when cement implantation can control the lesion [11].

3.5. Chordomas

Chordomas are malignant tumors which arise from notochord remnants, and therefore are typically midline or central in location anywhere from the Rathke’s pouch to the coccyx. Lesions are most commonly sacrococcygeal, with decreasing frequency in the spheno-occipital region,

Table 1. Summary of radiologic appearance of tumors included in the differential diagnosis with chordoma.

and vertebral body axis. Clival chordomas typically project in the midline and impinge upon the pons, producing a characteristic “thumb sign”. Chordomas of the vertebral bodies usually affect cervical and lumbar segments. Vertebral body lesions are often lytic bone lesions, at times with a sclerotic rim and calcification. Vertebral lesions may involve the disc space and contiguous vertebrae. CT imaging demonstrates a soft-tissue like mass with bony destruction and areas of calcification. On MR imaging, lesions appear hyperintense on T2WI with avid enhancement. On T1WI, chordomas are isointense to the spinal cord although areas of hypointense calcification may be identified. Chordomas are generally not sensitive to radiation or chemotherapy, consequently en bloc resection is advised. Intensity modulated radiation therapy (IMRT) and stereotactic radiosurgery (i.e. CyberKnife® or Gamma Knife®) are sometimes used to treat chordomas with varying results and relatively high complication rates in the cranial base location [12,13] . Chordomas are generally resistant to standard cytotoxic chemotherapy agents, however, some success has been reported with Gleevec® (imatinib) [14] and epidermal growth factor receptor inhibitors such as cetixumab and gefitinib [15,16] . Advances in photon and proton radiation therapy may provide positive results for poor surgical candidates and patients with recurrent tumor [17].

4. Conclusion

EACs are a rare but important consideration in the diagnosis of extra-axial lesions of the central nervous system. This case report emphasizes the need for neurosurgeons to be familiar with the variations in MRI appearance among these different entities because of its implications in presurgical planning. Due to the finding that conventional radiation therapy and chemotherapy are generally not useful treatments in chordomas, it is recommended that these patients undergo an aggressive surgical approach with the goal of a gross total resection. In these large paraspinous lesions that could represent a broad range of diagnoses, diagnostic needle biopsy is of great value as the results can effectively guide surgical planning. Survival, recurrence rates and rates of metastasis are largely unknown because of the rarity of this condition. More research is needed to define the role of photon therapy and newer advances in radiation and chemotherapy for those patients in which gross total resection cannot be achieved.

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NOTES

*Corresponding author.

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