Exencephaly is a type of cephalic disorder wherein the brain is located outside of the skull. This condition is usually found in embryos as an early stage of anencephaly. As an exencephalic pregnancy progresses, the neural tissue gradually degenerates.The prognosis for infants born with exencephaly is extremely poor. It is rare to find an infant born with exencephaly, as most cases that are not early stages of anencephaly are usually stillborn. Those infants who are born with the condition usually die within hours or minutes. Caused by the failure of cranial neuropore to properly fuse, between the 3rd and 4th week post conception. The calvarium doesnt develop/fuse properly, therefore the brain extrudes from the cranium. Pathophysiology
Until recently, the medical literature did not indicate a connection among many genetic disorders, both genetic syndromes and genetic diseases, that are now being found to be related. As a result of new genetic research, some of these are, in fact, highly related in their root cause despite the widely varying set of medical symptoms that are clinically visible in the disorders. Exencephaly is one disease that has recently been identified as part of an emerging class of diseases called cilopathies. The underlying cause may be a dysfunctional molecular mechanism in the primary cilia structures of the cell, organelles which are present in many cell types throughout the human body.
Trevor disease, also known as dysplasia epiphysealis hemimelica and Trevors disease, is a congenital bone developmental disorder. There is 1 case per million population. The condition is three times more common in males than in females. Presentation
This disorder is rare, and is characterised by an asymmetrical limb deformity due to localized overgrowth of cartilage, histologically resembling osteochondroma. It is believed to affect the limb bud in early fetal life. The condition occurs mostly in the ankle or knee region and it is always confined to a single limb. This usually involves only the lower extremities and on medial side of the epiphysis. It is named after researcher David Trevor. Diagnosis
Differential diagnosis
Trevor disease  can often mimic posttraumatic osseous fragments, synovial chondromatosis, ostechondroma, or anterior spur of ankle. It is not possible to distinguish DEH from osteochondroma on the basis of histopathology alone. Special molecular tests of the genes EXT1, EXT2 are used for the analysis of genetic expressions. These are within normal ranges in DEH, while they are lower in ostechondroma (owing to a mutation). These tests are expensive and the diagnosis is often made on clinical and radiological findings. Synovial chondromatosis occurs in a much older age group and can be ruled out on this basis. Treatment
Most reported cases of DEH in the literature have been treated surgically, usually with excision of the mass, as well as by the correction
of any deformity, while preserving the integrity of the affected joint as much as possible.