Purpose: We present a case of desmoplastic infantile astrocytoma of infancy initially diagnosed and managed as a porencephalic cyst. This discussion will highlight the important imaging features of this rare infantile tumor that distinguish this entity from a porencephalic cyst.

Case report:
A male full-term infant initially presented with increased head circumference with downward gaze deviation at 5 weeks of age and was thought to have a large right porencephalic cyst exerting mass effect on the right lateral ventricle that was resulting in hydrocephalus. A right VP shunt was placed, followed by a left VP shunt two months later, followed by a right shunt revision one month later when the head circumference continued to increase in size, after which he re-presented with increased downward gaze deviation with new nystagmus and lethargy. He presented to our tertiary medical center and was found to have a large cystic mass with a superficial solid component and a ventricular catheter traversing the mass, resulting in intracranial hemorrhage. The mass was resected with a pathologic diagnosis of desmoplastic infantile astrocytoma with focal anaplastic features positive for the TPM3-NTRK1 fusion gene.

Imaging findings:
On the initial non-contrast head CT at 43 days old, there was a large, right hemispheric cystic mass with a posterior peripheral soft tissue component with associated midline shift and enlargement of the left lateral and third ventricles. The cystic component of the mass was slightly more dense than CSF (9HU vs 4 HU). Post-procedural non-contrast CT head at 3 months old demonstrates a ventricular catheter traversing the cystic mass, which has now hemorrhaged. MR brain with contrast at 4 months old found a large right hemispheric enhancing mass with intratumoral and intraventricular hemorrhage with cerebellar tonsillar herniation.

Summary:
Desmoplastic infantile ganglioglioma or, as in this case, desmoplastic infantile astrocytoma of infancy where there was primarily an astrocytic component to the tumor, is a rare tumor seen in predominantly male infants. The typical presentation is with macrocephaly or seizures. Imaging often reveals a large, cystic and solid tumor in the cerebral cortex. The solid component can calcify and avidly enhances. In this case, the cystic component of the mass was slightly more dense than the CSF in the lateral ventricle and exerted significant mass effect, which would not typically be seen with a porencephalic cyst.

Desmoplastic Infantile Astrocytoma Misdiagnosed as a Porencephalic Cyst

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