Brown Sequard syndrome is typically associated with traumatic injuries, however other structural etiologies have also been reported. We report a case of a teenager with Brown-Sequard syndrome and bilateral vibration deficits, later diagnosed with mesenchymal chondrosarcoma (MCS).

A 14-year-old healthy, neurotypical teenager presented with decreased cold sensation in their right hand for 1 week followed by progressive left-arm weakness for 3 days prompting emergency care.

Neurologic examination showed low muscle bulk, absent right-sided pain and temperature sensation, rapidly progressing left-sided weakness, absent vibration bilaterally (except face and neck), hyperreflexia (worse on right side) with intact cranial nerves. MRI brain was not immediately possible due to braces, so he had CT head with contrast which showed significant spinal cord compression from an enhancing mass at the craniocervical junction. After braces were removed, MRI neuro-axis was completed and demonstrated a homogenously enhancing, calcified, lobulated lesion centered at the anterior foramen magnum with mass effect on the medulla, craniocervical junction, and proximal cervical cord.

The patient underwent gross-total resection. Pathology showed malignant mesenchymal neoplasm. RNA analysis identified fusion of HEY1:NCOA2, confirming diagnosis of MCS.

MCS is an extremely rare form of bone tumor, and diagnosis is often delayed as presenting symptoms can be highly variable. This case underscores the importance of thorough neurologic exam which found a Brown-Sequard-like syndrome, albeit with bilateral vibration loss, prompting emergent workup. It also highlights the importance of CT scans with contrast when MRI is not immediately an option. Atypical Brown-Sequard has not been reported in the pediatric population as the initial presentation for MCS. We aim to highlight a unique presentation of this highly malignant tumor.