Spinal pilocytic astrocytoma in an adult

Clinical History

A 38-year-old woman presented with lumbar pain that had increased during the past weeks especially with movements and decreased with bed resting. This pain radiated to the right lower limb and was associated with paraesthesias and disaesthesias.
The physical and neurological examination showed no abnormalities.

Imaging Findings

MRI was performed and showed a 13 mm predominantly cystic expansile lesion with a thick wall that showed marked rim enhancement. The location was difficult to establish if it was extramedullary with intramedullary invasion or intramedullary with extramedullary invasion. The lesion was associated with significant cord oedema inferiorly and superiorly.
The patient underwent surgery, where the diagnosis was made.

Discussion

Spinal MRI is the best technique for the evaluation of spinal cord lesions, which allows to locate it intramedullary or intradural extramedullary, narrowing the differential diagnosis. The difficulty of this case was first to distinguish if the lesion was intra, extramedullary or combined. Second, the rim enhancement with marked secondary intramedullary oedema was difficult to match with tumoral or cystic lesions.
The most important criteria to distinguish intramedullary neoplasms from non-neoplastic spinal cord lesions are cord expansion, lesion enhancement and associated cysts.
Intramedullary neoplasms usually show at least some degree of enhancement, in fact, the lack of enhancement is the primary imaging feature to differentiate this kind of neoplasms from other noneoplastic tumour-like conditions [1, 2].
Cystic tumoral lesions include cystic astrocytoma and ependymoma as the most common lesions, but also haemangioblastoma, ganglioneuroma or cystic meningioma, therefore this is not specific. Ependymoma is the most common intramedullary spinal tumour in adults; the myxopapillary variant is typically located in the conus medullaris and filum terminale [2, 3]. Both astrocytomas and ependymomas are generally associated with cord oedema and enlargement.
On the other hand, we must consider in our differential diagnosis some non-neoplastic spinal cord lesions such as epidermoid cyst or granulomatous diseases. Epidermoid cyst shows thin enhancement and is not associated with cord oedema. Granulomatous diseases, mainly TB but also sarcoid, have thick rim enhancement and might also be associated with cord oedema.
Pilocytic astrocytoma WHO grade I represents 5-10% of all gliomas and is the most common brain tumour in children (80% of them below 20 years of age), being a rare diagnosis in the adult population [4]. Most spinal astrocytomas are located in the upper thoracic spinal cord followed by cervical spine, very rarely in the conus medullaris. [4, 5]
A wide spectrum of clinical presentations exists. [5]
They are usually eccentric within the spinal cord. Usually they have inhomogeneous enhancement. Thus the classic MRI appearance of a spinal cord pilocytic astrocytoma is that of a cord-enlarging mass with associated oedema, located most often eccentrically, with a patchy and irregular pattern of contrast enhancement. [2]
The histological appearance is characterized by a biphasic pattern of two astrocyte populations: Compacted bipolar cells with Rosenthal fibres, and a loose-textured multipolar cell with microcysts and eosinophilic granular bodies. [2, 3]
As take home point we think low grade astrocytoma should be included in the differential diagnosis when ring or little enhancement in a predominantly cystic tumour of the cord is shown.

Differential Diagnosis List

Final Diagnosis

Spinal pilocytic astrocytoma, WHO grade I

URL:	https://eurorad.org/case/12586
DOI:	10.1594/EURORAD/CASE.12586
ISSN:	1563-4086