Among 3545 term or near term healthy neonates who underwent cranial ultrasound over a 2-year 5-month period at Mackay Memorial Hospital, Taipei, Taiwan, 18 (0.5%) were diagnosed with frontal horn cysts (FHCs). Seven were bilateral and 11 unilateral. The perinatal history was uneventful. FHCs are elliptical, smooth, thin-walled cysts located adjacent to the tip of the anterior horns of the lateral ventricles. Six resolved within 1 month, and 6 between 2 and 11 months of age. Ultrasound was not repeated to document resolution in 4, and 2 were lost to follow-up. One infant with an atypical FHC had an enlarged left FHC with midline shift on follow-up, but was normal in development. FHCs should be checked by repeat cranial ultrasound at 1 or 2 and 6 months of age. Infants with atypical FHCs require follow-up with CT or MRI. 
COMMENT. Frontal horn cysts in neonates are different from subependymal cysts, and most resolve spontaneously. The cause is unknown, but hypotheses include antepartum cerebral hemorrhage, infarction, ischemia, infection, and leukomalacia. Among 73 cases reported and cited by the authors, the incidence in premature and term infants is similar (0.48-0.91%), 38 were unilateral, 35 bilateral, 4 died, 2 were developmentally delayed, 5 had cerebral palsy, and 1 had seizures. The majority (84%) was normal on follow-up. The differential diagnoses include subependymal cyst, arachnoid cyst, porencephaly, and periventricular leukomalacia. This and four previous reports describe the frontal horn cyst in normal neonates as a separate entity with a benign course.