A 7-year-old child presents with progressive weakness of the lower limbs and gait disturbance over 6 months. MRI of the spine shows an eccentric intramedullary lesion in the cervical cord with T2 hyperintensity and indistinct margins, as marked **A** in the diagram. The lesion demonstrates patchy heterogeneous enhancement and is associated with a rostral syrinx. Based on the imaging characteristics of the structure marked **A**, which of the following is the most likely diagnosis?
A. Haemangioblastoma
B. Myxopapillary ependymoma
C. Ependymoma with haemosiderin cap
D. Pilocytic astrocytoma (WHO grade I)
Explanation
Why Pilocytic astrocytoma (WHO grade I) is right
The eccentric intramedullary T2 hyperintense lesion marked A with indistinct infiltrative margins, patchy heterogeneous enhancement, and associated rostral syrinx is the classic MRI signature of spinal cord astrocytoma. Astrocytomas are the most common intramedullary tumours in children and typically arise from cord parenchyma, growing eccentrically without respect to the central canal. The patchy enhancement pattern (not homogeneous) and absence of a haemosiderin cap sign further support astrocytoma over ependymoma. Low-grade pilocytic astrocytoma is the most frequent histological subtype in the paediatric population (Greenberg's Handbook of Neurosurgery, 9th ed; WHO 2021 CNS Tumour Classification).
Why each distractor is wrong
Ependymoma with haemosiderin cap: Ependymomas are more common in adults, arise from ependymal cells of the central canal (central/symmetric location), show intense well-defined homogeneous enhancement, and characteristically display a haemosiderin cap sign (T2 hypointensity at cranial/caudal margins). The eccentric location and patchy enhancement pattern here favour astrocytoma.
Haemangioblastoma: Associated with von Hippel–Lindau syndrome, haemangioblastomas present with an intensely enhancing small mural nodule surrounded by a large cyst. The diffuse eccentric infiltrative pattern and patchy enhancement shown in A do not match this entity.
Myxopapillary ependymoma: This is a specific subtype of ependymoma that arises from the conus medullaris and filum terminale, not the cervical cord. The imaging pattern and location are inconsistent with this diagnosis.
