Hazy enhancement seen in the perilesional edema immediately adjacent to ring-enhancing cystic neurocysticercosis lesion (NCC) on post-contrast T1-weighted images resembles the appearance of a solar corona and is known as the corona sign Figure 1.1 This sign is observed particularly in colloid-vesicular and granular nodular stages (stage 2 and 3) of NCC, when the parasitic cyst undergoes degeneration and patients become symptomatic with seizure or headache. The hazy enhancement likely represents a leaky blood–brain barrier (BBB) and is more common in young patients presenting with seizures. Corona sign is observed in only 1/5th of the patients but is an important additional imaging finding of NCC, especially representing an acute phase of symptomatic disease.1 Vesicular stage NCC usually presents as a solitary cyst with or without scolex and without ring enhancement/adjacent edema. However, in the active colloidal vesicular stage, the larva begins to degenerate from the scolex with turbid proteinaceous cyst fluid and thicker wall secondary to surrounding inflammatory response in the brain. Contrast enhancement of the cyst wall and adjacent parenchyma represents the breakdown of BBB by the inflammatory process.2,3 The presence of corona sign in a ring-enhancing cystic lesion with a scolex and inversion of cyst content on T2 FLAIR images can confirm a stage 2 NCC and prompt initiation of immediate appropriate therapy.Figure 1: Axial T2 3D FSE (a) image shows a T2 hyperintense cystic lesion with central scolex and a T2 hypointense wall with perilesional edema (white arrow). Axial post-contrast T1 image (b) shows a T1 hypointense cystic lesion with a ring-enhancing wall (curved white arrow) and hazy enhancement peripheral to the enhancing cyst wall (corona sign) (straight white arrow)Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Venkatraman Indiran (Sun,) studied this question.