[Brainstem dysgenesis: Möbius, Cogan and Pierre Robin syndromes revisited].

We propose the term brainstem dysgenesis to designate patients with congenital dysfunction of the cranial nerves and muscle tone due to prenatal lesions or anomalies of the brainstem. In some patients, the dysgenesis is genetically determined and can be isolated or form part of a more extensive polymalformation syndrome (mutations of organizing or regulatory genes). In most patients with brainstem dysgenesis, however, the disorder is caused by prenatal destructive or disruptive lesions of vascular origin. Depending on the vessels involved and the magnitude of the lesion, clinical manifestations can range from intrauterine death to mild involvement of several cranial nerves. Clinical findings in some of these patients may coincide with those described in Möbius, Pierre Robin or Cogan syndromes and, if that is the case, the eponym will indicate the location of the brainstem lesion. Clinical manifestations in most patients with brainstem dysgenesis, however, do not fit into any of the aforementioned syndromes. In these circumstances the term brainstem dysgenesis should be used followed by a detailed description of each patient's clinical findings and/or the brainstem segment presumably involved. The prognosis of patients with brainstem dysgenesis due to prenatal destructive lesions depends on the magnitude of the vascular territory involved and, in most cases, is better than the initial clinical manifestations would indicate.