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Two cases out of a sample of 41 fetuses and infants with prosencephalic malformation, observed at the Institute of Pathology and Department of Neuropathology of the University of Heidelberg, are described here in detail. These cases presented grossly with microcephaly and missing forebrain, appearing to be cases of aprosencephaly. However, in one of these cases glio-mesenchymal membranes with an ependymal outline, consistent with the microscopic appearance of the dorsal sac membrane in holoprosencephaly and obviously representing remnants of a collapsed primitive prosencephalic vesicle, could be demonstrated. In the other case only hindbrain structures, with the exception of the cerebellum, were present without any demonstrable remnants of a prosencephalon. We propose that the microscopic specification of a primitive prosencephalic vesicle in the first case and similar cases does not justify the diagnosis of atelencephaly/aprosencephaly because the prosencephalon was not really missing (pseudo-aprosencephaly). The prosencephalic anlage had been formed but remained vesicular without further differentiation of a holospheric brain mantle as in common holoprosencephaly ('vesicular forebrain'). We believe that pseudo-aprosencephaly represents the most primitive form of holoprosencephaly, in which the forebrain remains as a complete sac, linking classical holoprosencephaly with 'true' aprosencephaly, i.e., defective prosencephalic anlage due to developmental arrest. The 'vesicular forebrain' allows one to extend the classification of Probst by an additional category which might be termed complete sac category, intercalated between the dorsal sac category and 'true' atelencephaly/aprosencephaly.

The development of the pharyngeal pituitary (PhP) in the fetal period was morphologically and, for the first time, immunohistochemically examined. PhP, found in every individual, begins its hormone production at the 17-18th week of gestation, that is, 4-8 weeks later than that of sellar pituitary (SP). Only 1 of 25 examined fetuses without any stigmata of developmental anomalies showed a residual pituitary fragment in the craniopharyngeal canal (craniopharyngeal pituitary, CPhP). An adult case of a rare clivus pituitary adenoma that we examined is demonstrated in discussing its relationship to PhP. Extracranial ectopic pituitary adenomas in the literature describe an exclusively sphenoid sinus/nasopharyngeal/clivus location of the tumor. Their location corresponded exactly with that of PhP, so that the origin of the tumors can be reasonably speculated as PhP, although another origin, e.g., CPhP, can not be excluded. A variety of malformations of PhP, although very rare, have been described for the fist time during the systemic examination of 16 fetuses with different cranioneural malformations, such as agenesis, unseparated PhP from SP (pharyngosellar pituitary), fragmentation, and residual pituitary tissue in the open craniopharyngeal canal. However, developmental anomaly of PhP was not specifically associated with cranioneural malformations except in cases of chromosomal aberrations. The hormone production in PhP in malformation cases tended to be retarded. Absence of SP was recorded in 50% of anencephalics in the literature; however, PhP was identified in all anencephalics in our series, independent of the existence of SP. This supports the opinion that agenesis of SP in anencephalics seems to be false information.

A case of exencephaly associated with spinal dysraphism and Cantrell-Haller-Ravitsch syndrome is described. Significant findings included exencephaly, multiple subcortical neuroepithelial islets with active proliferation, cerebellar aplasia, and abnormal flexion of the neuraxis with spinal dysraphism of the cervicothoracic region. The various features of exencephaly, anencephaly, and iniencephaly are discussed. The significance of subcortical growth zones is evaluated in the light of experimental observation.s

Intrauterine purulent necrotizing encephalitis was found in a stillborn male of the 30th gestational week. The necrotizing process in the brain, prominent in the white matter, suggested an early stage of hydranencephaly.

A case is presented of almost complete destruction of the cerebellum secondary to a hemorrhagic event in utero. Lesions consistent with hydranencephaly were found in the territories of the vertebral-basilar circulation. Ependymitis and aqueduct occlusion secondary to the intraventricular bleeding resulted in intrauterine hydrocephalus formation.

Keratinous material, in the form of epithelial squames often with foreign body reaction and dense gliosis, was demonstrated in all of ten cases of anencephaly by a sensitive and specific immunohistochemical stain. In some cases keratin was not recognized on routine histological stains.

The gross and microscopic features of a 28-week-old stillborn female infant with severe cranial, facial, and cerebral malformations due to amniotic bands are described. The structure of the cerebral remnant is similar to that found in dysraphic anencephaly, but collateral evidence of amniotic band can usually be found. It is important to differentiate between the two conditions, since unlike neural tube defects, anencephaly due to amniotic band does not imply a risk of recurrence in subsequent pregnancies.