Late progression of incidental colloid cysts – Two case reports and a review of the literature

Colloid cysts are third ventricular lesions located most commonly within the roof of the third ventricle. Their location adjacent to the foramen of Monro poses the risk of developing acute obstructive hydrocephalus and death. Although large symptomatic lesions warrant surgical resection, many colloid cysts are small, asymptomatic and are discovered incidentally. Hence, the latter group of lesions are often managed conservatively with radiological surveillance imaging. The frequency and duration of imaging, however, is not well established. Our paper focuses on delayed clinical and radiological progression of incidentally discovered colloid cysts, highlighting the role of long-term surveillance imaging. We described two cases of incidental colloid cysts that progressed many years after initial diagnosis, and review the current literature to characterise the natural history of these lesions. Clinicians should be aware of possible late progression of colloid cysts, an uncommon but potentially significant phenomenon, and to institute early treatment if appropriate. We contend that annual long-term clinical and radiological surveillance should be routine practice even for small, asymptomatic colloid cysts.