If present, the physician should rule out serious conditions associated with the third fontanelle. Other animals
Primates
In apes the fontanelles fuse soon after birth. In chimpanzees the anterior fontanelle is fully closed by 3 months of age. Dogs
One of the more serious problems that can affect canines is known as an "open fontanelle", which occurs when the skull bones at the top of the head fail to close. The problem is often found in conjunction with hydrocephalus, which is a condition in which too much fluid is found within and around the brain, placing pressure on the brain and surrounding tissues. Often the head will appear dome-shaped, and the open fontanelle is noticeable as a "soft spot" on the top of the dogs head. The fluid-filled spaces within the brain, known as ventricles, also become swollen. The increased pressure damages or prevents the development of brain tissue.Not all open fontanelles are connected with hydrocephalus. In many young dogs the skull bones are not fused at birth, but instead will close slowly over a three- to six-month period. Occasionally these bones fail to close, but the dog is still healthy. In these cases, however, the dogs owners need to be very careful, since any injury or bumps to the animals head could cause significant brain damage, as well as conditions like epilepsy. An open fontanelle, known as a "molera", is a recognized feature of the Chihuahua breed.
Further studies are needed to determine which, if any, of these pathways are overactive in and can be successfully targeted with specific drug therapies to treat NF and its variants.Two cases of NF have tumor cells in which the USP6 gene has fuses with the  PPP6R3 (i.e. protein phosphatase 6 regulatory subunit 3) gene. In both of these cases, the tumors clearly showed malignant behavior. Diagnosis
NF may resemble and therefore be misdiagnosed as dermatofibrosarcoma protuberans, fibrosarcoma, malignant fibrous histiocytoma, spindle-cell melanoma (a rare form of melanoma,) leiomyosarcoma, and inflammatory myofibroblastic tumor. The diagnosis of NF and its variants depends on a combination of findings no single one of which is definitive. These findings are: the tumors: presentation (particularly its location in the cranium, within blood vessels, or outside of these areas); histopathology (particularly analyses of tumor cell mitoses which if atypical strongly suggest the tumor is not NF); presence of myofibroblasts that typically express muscle-specific actin, SMA, and vimentin and may express CD68 but generally do not express S100, desmin, trypsin, factor VIII, F4/80, or CD34 (lack of Cd34-expressing cells indicates that the tumor is not a sarcoma); and presence of typical neoplastic cells expressing an USP6-containing fusion gene. (USP6-containing fusion genes also occur in the tumor cells of aneurysmal bone cysts, fibroma of tendon sheaths, giant cell reparative granuloma, and myositis ossificans/fibro-osseous pseudotumor of digits.)