Mesenchymal Chondrosarcoma Presenting as Atypical Brown–Sequard Syndrome

1. Introduction

Brown–Sequard syndrome results from hemisection of the spinal cord, producing ipsilateral motor weakness and loss of proprioception with contralateral loss of pain and temperature sensation. It is commonly associated with penetrating spinal trauma. Nontraumatic etiologies, particularly tumors at the craniocervical junction, are rare and may have atypical presentations leading to delayed diagnosis. We report an unusual case of atypical Brown–Sequard syndrome in an adolescent caused by a rare mesenchymal tumor at the foramen magnum.

2. Patient Presentation

This 14‐year‐old previously healthy boy presented with a 1‐week history of cold sensation loss in the right hand and progressive weakness in the left hand. His neurological examination revealed left hemiparesis, hyperreflexia with Babinski sign, and diminished pain and temperature sensation on the right. His cranial nerve examination was normal without evidence of Horner syndrome. Vibration sensation was mildly reduced bilaterally, suggesting partial involvement of the dorsal column–medial lemniscus pathway. Overall, the neurological examination was consistent with a hemicord syndrome localizing to the upper cervical cord. Contrast‐enhanced computed tomography of the head and cervical spine demonstrated a calcified, heterogeneously enhancing craniocervical junction mass with cord compression (Figure 1A–C). Magnetic resonance imaging revealed a lobulated, homogeneously enhancing tumor centered at the anterior foramen magnum with mass effect on the medulla, craniocervical junction, and proximal cervical cord (Figure 1D–H). Neuroimaging features were most consistent with chordoma, meningioma, or sarcoma.

Figure 1.

Computed tomography of the brain and cervical spine at presentation demonstrated a calcified anterior craniocervical junction mass (A, arrow) with associated contrast enhancement (B,C, arrows). Magnetic resonance imaging demonstrated extensive cervical cord compression (D, arrow), no evidence of reduced or facilitated diffusion on apparent diffusion coefficient sequences (E, arrow), significant susceptibility weighted artifact (F, arrow), hypointensity on T2‐weighted sequences without invasion of the adjacent jugular foramen (G, arrow), and avid enhancement on post‐T1 weighted sequences (H, arrow).

The patient underwent gross total resection without complications. Three days postoperatively, he showed significant improvement in strength and temperature sensation. Histopathology demonstrated a biphasic tumor composed of sheets of malignant small round blue cells intermixed with nodules of hyaline cartilage (Figure 2). RNA sequencing identified a HEY1::NCOA2 fusion, confirming a diagnosis of mesenchymal chondrosarcoma (MCS). Postoperative treatment with chemotherapy (vincristine, doxorubicin, cyclophosphamide, ifosfamide, etoposide) and focal proton radiation resulted in complete response without evidence of tumor recurrence more than 1 year post diagnosis.

Figure 2.

Tumor histopathology revealed a biphasic tumor composed of sheets of malignant round blue cell tumor admixed with nodules of hyaline cartilage. (Hematoxylin and Eosin stain, A, magnification ×100 and B, magnification ×200). Subsequent RNA sequencing identified a HEY1::NCOA2 fusion, consistent with a diagnosis of mesenchymal chondrosarcoma.

3. Discussion

Primary spinal cord tumors are uncommon in children and typically present with a slow, indolent course. Reported median time to diagnosis is up to 7.8 months, with over one‐third of patients experiencing symptoms for more than 6 months before diagnosis [1]. Prolonged symptom duration strongly predicts neurological sequelae, with delayed presentation increasing the risk of permanent deficits by approximately 16‐fold [2]. MCS is a rare and aggressive subtype of chondrosarcoma, accounting for approximately 1% of all cases, predominantly affecting adolescents and young adults [3]. These tumors may arise from bone or soft tissue, commonly involving craniofacial bones, spine, sacrum, or trunk [4]. Pediatric spinal cord compression due to mesenchymal chondrosarcoma has rarely been reported [5]. The HEY1::NCOA2 fusion is the defining molecular feature of MCS, present in the majority of cases [6]. Surgical resection with wide margins remains the cornerstone of treatment, often followed by adjuvant chemotherapy and radiation therapy. This is the first reported case of mesenchymal chondrosarcoma presenting with an atypical Brown–Sequard syndrome in an adolescent. This patient highlights the importance of recognizing atypical presentations of nontraumatic spinal cord syndromes. Earlier recognition of the signs and symptoms associated with spinal cord compression may lead to prompt neurosurgical management and reduce long‐term neurological sequelae.

Author Contributions

Naman D. Shah: data curation, writing – original draft, writing – review and editing. Adam Z. Kalawi: writing – original draft, writing – review and editing. Rachel Pearson: writing – review and editing. Ali Nael: data curation, writing – review and editing. John R. Crawford: conceptualization, data curation, writing – original draft, writing, supervision.

Funding

The authors have nothing to report.

Ethics Statement

This case report is exempt from institutional review board review.

Conflicts of Interest

John Crawford serves as an associate editor of the Annals of the Child Neurology Society. The other authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.