Malformations of the brainstem in 138 patients identified aver a 10 year period are classified according to MRI findings and by embryological cause in a study at University of California at San Francisco, and University of Chicago, IL. The pons was involved in 114, midbrain in 45, and medulla in 14. More than 1 region was affected in 53 patients. Malformations were classified in four groups: 1) disorder of brainstem segmentation or induction; 2) segmental hypoplasia; 3) postsegmentation malformation (associated with migration abnormalities); and 4) abnormal cortical organization. Segmentation anomalies included short pons, short midbrain/long pons with large cerebellum, and thick, short medulla. Segmental hypoplasia involving the pons in 59 patients was associated with microcephaly in 34. Postsegmentation anomalies included midbrain enlargement, enlarged quadrigeminal plates, midline clefts, 33 with congenital muscular dystrophies and Oglycosylation defects (10 with Walker-Warburg syndrome, 7 with muscle-eye-brain disease, and 2 with Fukuyama CMD), and 19 with Joubert's syndrome and the characteristic molar tooth malformation. Associated cortical organization abnormalities included polymicrogyria and cerebellar hypolasia with pontine hypoplasia in 11 patients. Disorders involving the cranial nerves usually had no brainstem abnormalities on imaging other than hypoplasia of the affected nerves. 
COMMENT. Brainstem malformations appear to be more common than generally recognized. This study and proposed classification should alert neurologists and radiologists to the diagnosis of congenital malformation of the brainstem in infants and children with nonprogressive cranial nerve and long tract signs. We can look forward to an anticipated separate account of cerebellar malformations from the same institutions. Intrauterine ischemic atrophy rather than a primary developmental malformation is suggested in some reports of brainstem lesions presenting with congenital apnea and failure of central respiratory drive  Reviewed by Sarnat HB. Recent advances in congenital malformations. In: Progress in Pediatric Neurology III, Chicago, PNB Publ, 1997;365-369.