Lumbar Extradural Extraskeletal Ewing Sarcoma with Psoas Denervation: A Case Report

Introduction

Extraskeletal Ewing sarcoma (EES) is a rare malignant small round cell neoplasm that originates from common mesenchymal stem cells [1]. Its overall incidence is approximately 15% to 20% of that of Ewing sarcoma of bone [2]. EES shares a common genetic lineage with Ewing sarcoma of bone, and distinction between the two is based on anatomic location of the tumor subtypes. The most commonly reported location of EES is within the paravertebral region, and it can manifest as either intradural and/or extramedullary or extradural in anatomic location [3,4]. Skeletal muscle denervation can be caused by nerve compression or traction, resulting in muscle edema and leading to fatty atrophy in cases of chronic denervation [5]. The psoas is innervated by the lumbar plexus nerve. Lumbar extradural EES compressing the lumbar plexus nerve and causing psoas denervation is extremely rare.

To the best of our knowledge, no reports to date have described psoas denervation attributed to lumbar extradural EES compressing the lumbar plexus nerve. We herein report a biopsy-confirmed case of extradural EES located in the lumbar region and accompanied by psoas denervation. The imaging presentation of this unique case and the etiology of the muscle denervation are also discussed in this report.

Case Report

A 38-year-old Chinese man presented with a 1-month history of thoracolumbar pain that worsened at night and had become progressively more severe. His medical history was unremarkable. Physical examination revealed alignment straightening of the thoracolumbar vertebrae. He exhibited limitations of thoracolumbar flexion, extension, and lateroversion, as well as tenderness of the thoracolumbar spinal processes and paravertebral muscles.

Magnetic resonance imaging (MRI) of the lumbar spine revealed a lobulated mass in the left paravertebral region (Figure 1). The mass measured approximately 31×47×42 mm and had a well-defined margin. It showed intermediate signal intensity on T1-weighted imaging with mild heterogeneity and hyperintensity on short tau inversion recovery (STIR) images (Figure 1A, 1B). Patchy hyperintensity was observed on T1-weighted MRI (Figure 1A). The psoas was compressed and showed feathery increased signal intensity on T2-weighted images, while having maintained muscle texture (Figure 1A–1C). Axial MRI showed that the mass extended into the L1-L2 intervertebral foramen and compressed the thecal sac (Figure 1D). The mass and edematous psoas showed a significant increase in signal intensity on MRI after gadolinium-based contrast enhancement (Figure 2A, 2B).

The patient underwent computed tomography (CT)-guided percutaneous core needle biopsy and immunohistochemistry (Figure 3). Histopathological examination revealed clusters of atypical small blue round cells with hyperchromatic nuclei, scant cytoplasm, and frequent mitotic figures (Figure 4A). Immunohistochemistry showed positivity for NKX2.2 (Figure 4B) and CD99 (Figure 4C). Overall, these findings were consistent with EES.

Computed tomography of the lungs revealed multiple nodules in the bilateral pulmonary fields (Figure 5). Based on the clinical, imaging, and histopathological findings, the patient received a diagnosis of pulmonary metastases.

The patient was treated nonsurgically because of the multiple pulmonary metastases. However, the tumor showed no response to 4 cycles of chemotherapy consisting of vincristine, doxorubicin, and cyclophosphamide. The patient refused further chemotherapy and accepted only oral analgesics. He died 12 months after presentation to our hospital.

Discussion

EES was first recognized by Tefft et al in 1969 [6]. EES is rare in comparison with Ewing sarcoma of bone [7]. It can occur at any site in the body and presents as a bulky soft tissue mass. The most commonly reported locations of EES are the paravertebral region (32%), lower extremities (26%), chest wall (18%), retroperitoneum (11%), pelvis and hip (11%), and upper extremities (3%) [8–10]. The lesion usually manifests in young patients, with 85% of cases detected in patients between 20 months and 30 years of age [11]. Importantly, in the adult population, these extraskeletal tumors are more common than Ewing sarcoma of bone.

EES that originates around the spinal column is very rare. In patients with paravertebral EES, the most common clinical symptoms at presentation include radicular pain, lower extremity paresis, sensory disturbances, and symptoms of cord compression, such as bowel or bladder dysfunction [10]. MRI is also useful for determining the extent of local involvement with surrounding structures. A diagnostic criterion of EES is the absence of osseous involvement on MRI. However, EES can cause adjacent bone erosion, cortical thickening, osseous invasion, or aggressive periosteal reaction in 25% to 42% of cases [8,10]. In the present case, the adjacent vertebral body cortex was intact, and no marrow edema was present; these findings indicated that the mass did not involve the adjacent bone.

Spontaneous hemorrhage can lead to rapid growth of a mass [11]. Relative to muscle, tumors are typically isointense to hyperintense on T1-weighted images and hyperintense on T2-weighted images. Smaller tumors tend to be homogeneous; heterogeneity on unenhanced and contrast-enhanced images is typically seen for larger tumors and is related to hemorrhage and internal necrosis [11]. Areas of hemorrhage appear as high signal intensity on all pulse sequences and are not uncommon. Consistent with this, the mass in the present case showed hemorrhage, with the hemorrhagic area showing enhancement on post-contrast images.

We have herein reported an extradural EES that was located in the left paravertebral area, extended into the L1-L2 intervertebral foramen, and compressed the thecal sac. The diffuse increased signal of the psoas major muscle on STIR images was preliminarily misdiagnosed as soft tissue inflammatory edema. Subsequent biopsy with pathological and immunohistochemical examinations revealed findings consistent with EES. Based on these findings, as well as the location of the mass and the lumbar plexus supply of the psoas major muscle, the final diagnosis in our case was paravertebral extradural EES with psoas denervation.

Muscle denervation can be caused by numerous abnormalities, including nerve entrapment. Compression of a nerve causes swelling that is thought to be due to the blockage of axonal transport; ischemia can also play a role [5]. MRI is a preferred modality to diagnose muscle denervation. In acute denervation, fluid-sensitive images reveal homogeneous edema within the affected muscle, corresponding to the distribution of the damaged nerve. Three cardinal signs that help in the diagnosis of denervation are usually present. First, the edema is confined inside the muscle and does not extend beyond the muscle fascia. Second, there is a lack of associated fascial edema. Third, on T1-weighted images, the affected muscles exhibit their normal muscle architecture and signal intensity. Contrast enhancement on MRI in denervated muscle 48 h after denervation has been described and was presumably caused by increased capillary permeability [12].

The lumbar plexus is a network of nerves that arises from the anterior rami of spinal nerves L1–L4. It is located anterior to the transverse processes of the lumbar vertebrae. The main branches of the lumbar plexus can be organized into groupings relative to the psoas major muscle. These branches emerge lateral, anterior, or medial to the muscle. The tumor in the present case was located in the left paravertebral region and extended into the L1–L2 intervertebral foramen, and 1 branch of the lumbar plexus was compressed by the mass. The MRI characteristics of the psoas major muscle were consistent with muscle denervation. Additionally, the morphology of the soft tissue mass was irregular, and the mass showed heterogenous intensity on T1- and T2-weighted imaging. These findings were consistent with a tumor rather than an abscess.

Conclusions

Psoas major muscle denervation caused by extradural EES is extremely rare. Correct identification of muscle denervation may help prevent the misdiagnosis of a primary lesion.