Answer: Baylisascaris procyonis, the raccoon intestinal roundworm
Eggs of this nematode get into the environment and may be accidentally ingested by humans (typically young children) resulting in visceral larva migrans (VLM) as shown in this case. The larvae hatch from the ingested eggs and enter the blood stream to migrate readily throughout the body, with a predilection for the brain and spinal cord.
The diagnosis can be made by serology (available only at specialized centers) in association with a suggestive clinical presentation or through finding characteristic larvae in tissues. A peripheral eosinophilia and eosinophilic response in tissue sections is common.
The larvae are relatively large (50-60 microns in diameter) and have lateral alae (arrows below), and excretory columns (internal and adjacent to the alae). They also have multinucleated intestinal cells (not shown well here)
Not the presence of eosinophils and associated necrosis.
The differential diagnosis includes VLM due to Toxocara species which also have lateral alae and excretory columns, although these larvae are smaller in diameter (15-20 microns in diameter).