The simple fact that a Chihuahua has a domed head with an open molera does not predispose it to hydrocephalus as found by a study done by Greene and Braund in 1989, "Many clinically normal toy breeds and brachycephalic (short faced) breeds also may have open fontanelles without associated hydrocephalus." (Diseases of the Brain) Also, "There did not appear to be any relationship between the presence or size of the fontanelle and the concomitant presence of hydrocephalus." When the dog seems normal but displays enlarged ventricles of the brain (under ultrasound) its hydrocephalus is termed "occult" (having no clinical signs).

Diagnosis of hydrocephalus can only be ascertained by ultrasound. There are certain neurological signs that point to a suspicion of hydrocephalus such as: "lack of coordination, ventrolateral or lateral strabismus (eyes focused to the sides leaving large white crescents at the inner corners), involuntary movements of the eyeballs, visual deficits, short attention span, seizures, decreased righting reflex, depression with periods of apnoea (suspended breathing) and/or tetraparesis" (paralysis). In addition there may be "developmental or congenital abnormalities such as lack of permanent teeth, stenoic nares (constricted nasal passages), torticollis (neck twisted and head turned to one side) or physical immaturity." The vision defects may go so far as to include "total lack of vision, propulsive activity, circling, pacing and abnormal behaviour, excessive aggression, lethargy or difficult in training".

The prognosis for a dog with hydrocephalus is generally unfavourable, whether the animal has a molera or not, is irrelevant. The condition is usually congenital meaning it is present at birth although it may not be noticeable and may go undiagnosed until at some time later it declares itself by showing symptoms and causing the animal some problem. It can of course be caused through trauma, this may be of varying degrees, and the trauma itself may have gone unnoticed. Animals that have been diagnosed with hydrocephalus can sometimes have a shunt inserted to drain the excess fluid away from the brain but as stated previously the prognosis is not good. There are many dogs whose life expectancy has been increased, and made near normal for years after shunting, but sadly some fail and die shortly after the procedure.

The Chihuahua club of America has brought the historical insistence of a molera to the attention of numerous veterinary colleges. It has been gratifying to have the acquiescence of a top neurologist/neuroanatomist, Dr Alexander de Lahunta of Cornell University in New York, who wrote, "I do think it is wrong to conclude any opening is abnormal. .I would personally agree with a standard that accepted an open suture of minimal size in the breed." The clubs preliminary study has resulted in the following proportions: Only 15.7% moleras had closed by eighteen months of age, but thereafter, over 50% ultimately closed. 1.6% remained nickel sized or over at eighteen months of age. Some may take up to three years to close, and others may never close.

Concern is voiced regarding the effects of blows to the skull and rightly so. If such an unseemly happening did occur, at least the Chihuahua with a molera would have space for the brain to swell and heal. Blows, more likely than causing rupture of the molera, might result in prolapse of an eyeball since dogs’ eyeballs are not surrounded by bone and constricted within the skull, as are humans. In any case, the Chihuahua should be treated with care and lovingly handled. They are exceedingly tough little fellows with lives spanning up to two decades. Chihuahuas were bred only to please you. Keep them close to your side and return the love they give so unstintingly.

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