Frontal horn thin walled cysts in preterm neonates are benign

Background-Screening cranial ultrasound led to the discovery of isolated fr ontal horn cysts quite distinct from periventricular leucomalacia cysts. Aim-To clarify their significance, incidence, characteristics, causal facto rs or aetiology, and effect on long term outcome. Design-A retrospective observational study of all first cranial ultrasound scans (total of 2914) performed during the period 1984-1994 inclusive found 21 neonates with smooth thin walled frontal horn cysts: 18 of 2629 scanned were of birth weight < 1500 g or gestation < 33 weeks, and three of 285 we re > 33 weeks gestation. Sequential ultrasound, maternal records, and neona tal events were retrospectively assessed. In survivors, routine neurodevelo pmental evaluations were obtained. Postmortem studies of one cyst were perf ormed to determine the nature and origin of these lesions. Results-Of the 21 subjects, 15 had isolated frontal horn cysts and six had additional ultrasound scan abnormalities, including four with subependymal haemorrhage. The sonographic features of frontal horn cysts were of distinc tive morphology (elliptical, smooth, thin walled, ranging in size from 3 to 20 mm) and position (adjacent to the tip of the anterior horns). The cysts enlarged and then regressed by a median corrected age of 2 months. Subject s of < 33 weeks gestation (n = 18) had a median birth weight of 1465 g (ran ge 720-1990) and median gestation of 30 weeks (range 24-32). There was no c onsistent perinatal course. The neurodevelopmental outcome in 10 of the 11 survivors with isolated frontal horn cysts was normal. Five subjects died f rom causes unrelated to brain pathology in the neonatal period, and one sub ject died after infancy. Histological examination of a cyst at autopsy in o ne additional subject subsequent to the period of study confirmed the cyst to be lined by neuroblasts and ependymal cells. Conclusions-The incidence of frontal horn cysts in this low birthweight pop ulation was 7 per 1000 (0.7%) subjects scanned. They are present in the fir st week of life, enlarge, and resolve spontaneously. Survivors with isolate d frontal horn cysts appear to have normal neurodevelopmental outcome. The prognosis of these distinct frontal horn cysts therefore appears to be beni gn.