Hypomimia (masked facies, masking of facies), a medical sign, is a reduced degree of facial expression. It can be caused by motor impairment (for example, weakness or paralysis of the facial muscles), as in Parkinson's disease, or by other causes, such as psychological or psychiatric factors (for example, if a patient does not feel emotions and thus does not show any expression).

Persons receiving excessive Botox treatments, and thusly losing disproportionate facial expression features may be incorrectly identified as suffering hypomimia.

Foroozen divides the causes of chiasmal syndromes into intrinsic and extrinsic causes. Intrinsic implies thickening of the chiasm itself and extrinsic implies compression by another structure. Other less common causes of chiasmal syndrome are metabolic, toxic, traumatic or infectious in nature.

Intrinsic etiologies include gliomas and multiple sclerosis. Gliomas of the optic chiasm are usually derived from astrocytes. These tumors are slow growing and more often found children. However, they have a worse prognosis, especially if they have extended into the hypothalamus. They are frequently associated with neurofibromatosis type 1 (NF-1). Their treatment involves the resection of the optic nerve. The supposed artifactual nature of Wilbrand's knee has implications for the degree of resection that can be obtained, namely by cutting the optic nerve immediately at the junction with the chiasm without fear of potentially resulting visual field deficits.

The vast majority of chiasmal syndromes are compressive. Ruben et al. describe several compressive etiologies, which are important to understand if they are to be successfully managed. The usual suspects are pituitary adenomas, craniopharyngiomas, and meningiomas.

Pituitary tumors are the most common cause of chiasmal syndromes. Visual field defects may be one of the first signs of non-functional pituitary tumor. These are much less frequent than functional adenomas. Systemic hormonal aberrations such as Cushing’s syndrome, galactorrhea and acromegaly usually predate the compressive signs. Pituitary tumors often encroach upon the middle chiasm from below. Pituitary apoplexy is one of the few acute chiasmal syndromes. It can lead to sudden visual loss as the hemorrhagic adenoma rapidly enlarges.

The embryonic remnants of Rathke’s pouch may undergo neoplastic change called a craniopharyngioma. These tumors may develop at any time but two age groups are most at risk. One peak occurs during the first twenty years of life and the other occurs between fifty and seventy years of age. Craniopharyngiomas generally approach the optic chiasm from behind and above. Extension of craniopharyngiomas into the third ventricle may cause hydrocephalus.

Meningiomas can develop from the arachnoid layer. Tuberculum sellae and sphenoid planum meningiomas usually compress the optic chiasm from below. If the meningioma arises from the diaphragma sellae the posterior chiasm is damaged. Medial sphenoid ridge types can push on the chiasm from the side. Olfactory groove subfrontal types can reach the chiasm from above. Meningiomas are also associated with neurofibromatosis type 1. Women are more prone to develop meningiomas.

Chiasmal syndrome is the set of signs and symptoms that are associated with lesions of the optic chiasm, manifesting as various impairments of the sufferer's visual field according to the location of the lesion along the optic nerve. Pituitary adenomas are the most common cause; however, chiasmal syndrome may be caused by cancer, or associated with other medical conditions such as multiple sclerosis and neurofibromatosis.

Other causes may include:

- Diabetes mellitus

- Facial nerve paralysis, sometimes bilateral, is a common manifestation of sarcoidosis of the nervous system, neurosarcoidosis.

- Bilateral facial nerve paralysis may occur in Guillain–Barré syndrome, an autoimmune condition of the peripheral nervous system.

- Moebius syndrome is a bilateral facial paralysis resulting from the underdevelopment of the VII cranial nerve (facial nerve), which is present at birth. The VI cranial nerve, which controls lateral eye movement, is also affected, so people with Moebius syndrome cannot form facial expression or move their eyes from side to side. Moebius syndrome is extremely rare, and its cause or causes are not known.

The incidence of hemifacial spasm is approximately 0.8 per 100,000 persons. Hemifacial spasm is more prevalent among females over 40 years of age. The estimated prevalence for women is 14.5 per 100,000 and 7.4 per 100,000 in men. Prevalence for hemifacial spasm increase with age, reaching 39.7 per 100,000 for those aged 70 years and older. One study divided 214 hemifacial patients based on the cause of the disease. The patients who had a compression in the facial nerve at the end of the brain stem as the primary hemifacial spasm and patients who had peripheral facial palsy or nerve lesion due to tumors, demyelination, trauma, or infection as secondary hemifacial spasm. The study found that 77% of hemifacial spasm is due to primary hemifacial spasm and 23% is due to secondary hemifacial spasm. The study also found both sets of patients to share similar age at onset, male to female ratios, and similar affected side. Another study with 2050 patients presented with hemifacial spasm between 1986 and 2009, only 9 cases were caused by a cerebellopontine angle syndrome, an incidence of 0.44%.

The mechanism of action of benign paroxysmal torticollis is not yet understood. It has been suggested that unilateral vestibular dysfunction or vascular disturbance in the brain stem may be responsible for the condition.

The cause of benign paroxysmal torticollis in infants is thought to be migrainous. More than 50% of infants have a family history of migraine in first degree relatives. The cause is likely to be genetic.

The cause of Primrose syndrome is currently unknown. This condition is extremely rare and seems to spontaneously occur, regardless of family history.

In the case studied by Dalai et al. in 2010, it was found that an abnormally high amount of calcitonin, a hormone secreted by the thyroid gland to stabilize blood calcium levels, was present in the blood serum. This suggests that the thyroid gland is releasing an abnormal amount of calcitonin, resulting in the disruption of calcium level homeostasis. No molecular cause was found, but an expanded microarray analysis of the patient found a 225.5 kb deletion on chromosome 11p between rs12275693 and rs1442927. Whether or not this deletion is related to the syndrome or is a harmless mutation is unknown. The deletion was not present in the patient's mother's DNA sample, but the father's DNA was unavailable.

Macrostomia, (from the Greek prefix "makro-" meaning "large" and from Greek , "mouth") refers to a mouth that is unusually wide.

Macrostomia is characterized as a physical abnormality that causes clefts to form on the face of affected individuals. These clefts can form on either or both sides of the face, but they are most commonly seen on the right cheek and have a higher rate of occurrence in males. Macrostomia is very irregular and on average occurs only once in every 150,000 to 300,000 live births. It's unusual for macrostomia to occur on its own and it is included as a symptom for many diseases including craniofacial microsomia. The clefts result from improper development and fusion of the mandibular and maxillary processes. The clefts cause problems with facial muscle development. The origin of macrostomia is not yet fully understood it could have multiple causes.

Central facial palsy can be caused by a lacunar infarct affecting fibers in the internal capsule going to the nucleus. The facial nucleus itself can be affected by infarcts of the pontine arteries.

Almost all cases of synkinesis develop as a sequel to nerve trauma (the exception is when it is congenitally acquired as in Duane-Retraction Syndrome and Marcus Gunn phenomenon). Trauma to the nerve can be induced in cases such as surgical procedures, nerve inflammation, neuroma

, and physical injury.

The predominant cause of nutritional optic neuropathy is thought to be deficiency of B-complex vitamins, particularly thiamine (vitamin B), cyanocobalamin (vitamin B) and recently copper Deficiency of pyridoxine (vitamin B), niacin (vitamin B), riboflavin (vitamin B), and/or folic acid also seems to play a role. Those individuals who abuse alcohol and tobacco are at greater risk because they tend to be malnourished. Those with pernicious anemia are also at risk due to an impaired ability to absorb vitamin B from the intestinal tract.

In industrialized nations, toxic and nutritional optic neuropathy is relatively uncommon and is primarily associated with specific medications, occupational exposures, or tobacco and alcohol abuse. However, in developing nations, nutritional optic neuropathy is much more common, especially in regions afflicted by famine. Both genders and all races are equally affected, and all ages are susceptible.

Synkinesis is an interaction of nerves with muscles (although glands can also be involved). Most cases involve the cranial nerves which innervate many small cranial muscles, such as the facial muscles and the extraocular muscles. This is in contrast to areas of body where miswiring of the larger muscles is less evident due the size of the muscles. Synkinesis can also involve the upper limbs, especially hands which is quite rare, at 1 case in 1 million.

Microvascular decompression appears to be the most popular surgical treatment at present. Microvascular decompression relieves pressure on the facial nerve, which is the cause of most hemifacial spasm cases. Excellent to good results are reported in 80% or more cases with a 10% recurrence rate. In the present series approximately 10% had previously failed surgery. Serious complications can follow microsurgical decompressive operations, even when performed by experienced surgeons. These include cerebellar haematoma or swelling, brain stem infarction (blood vessel of the brain stem blocked), cerebral infarction (ischemic stroke resulting from a disturbance in the blood vessels supplying blood to the brain), subdural haematoma and intracerebral infarction (blockage of blood flow to the brain). Death or permanent disability (hearing loss) can occur in 2% of patients of hemifacial spasm.

Pallor is a pale color of the skin that can be caused by illness, emotional shock or stress, stimulant use, or anemia, and is the result of a reduced amount of oxyhaemoglobin and is visible in skin conjuctivae or mucous membrane.

Pallor is more evident on the face and palms. It can develop suddenly or gradually, depending on the cause. It is not usually clinically significant unless it is accompanied by a general pallor (pale lips, tongue, palms, mouth and other regions with mucous membranes). It is distinguished from similar presentations such as hypopigmentation (lack or loss of skin pigment) or simply a fair complexion.

Because the cause of facial clefts still is unclear, it is difficult to say what may prevent children being born with facial clefts. It seems that folic acid contributes to lowering the risk of a child being born with a facial cleft.

Ramsay Hunt syndrome type 2 refers to shingles of the geniculate ganglion. After initial infection, varicella zoster virus lies dormant in nerve cells in the body, where it is kept in check by the immune system. Given the opportunity, for example during an illness that suppresses the immune system, the virus travels to the end of the nerve cell, where it causes the symptoms described above.

The affected ganglion is responsible for the movements of facial muscles, the touch sensation of a part of ear and ear canal, the taste function of the frontal two-thirds of the tongue, and the moisturization of the eyes and the mouth. The syndrome specifically refers to the combination of this entity with weakness of the muscles activated by the facial nerve. In isolation, the latter is called Bell's Palsy.

However, as with shingles, the lack of lesions does not definitely exclude the existence of a herpes infection. Even before the eruption of vesicles, varicella zoster virus can be detected from the skin of the ear.

There are 4 distinct variations of macrostomia. Classifications are a complete lateral facial cleft, simple macrostomia, macrostomia with diastasis of the facial musculature, and isolated facial musculature diastasis. Each has a different physical appearance with varying levels of severity.

The cleft associated with macrostomia is associated with improper or failed fusion of the mandibular and maxillary processes during embryonic development. This can lead to a variety of abnormalities involving skin, subcutaneous tissue, facial muscles, and the mucous membrane. The severity of each abnormality can vary from minor to severe. Environmental contaminants may play a role in causing macrostomia. Many affected individuals were found in Lagos, an industrial area of Nigeria, where water supplies are known to be contaminated by improper disposal of industrial and domestic waste.

Treatment with the steroid "prednisone" and the antiviral drug "acyclovir 800mg 5 times a day" is controversial, with some studies showing to achieve complete recovery in patients if started within the first three days of facial paralysis, with chances of recovery decreasing as treatment was delayed. Delay of treatment may result in permanent facial nerve paralysis. However, some studies demonstrate that even when steroids are started promptly, only 22% of all patient achieve full recovery of facial paralysis.

Treatment apparently has no effect on the recovery of hearing loss. Diazepam is sometimes used to treat the vertigo.

The common symptoms in all reported cases of primrose syndrome include ossified pinnae, learning disabilities or mental retardation, hearing problems, movement disorders (ataxia, paralysis, and parkinsonism among others (likely due, in part, to calcification of the basal ganglia), a torus palatinus (a neoplasm on the mouth's hard palate), muscle atrophy, and distorted facial features. Other symptoms usually occur, different in each case, but it is unknown whether or not these symptoms are caused by the same disease.

Its exact cause is unknown, but present research points toward a genetic component, possibly following maternal genes.

It involves hypomethylation of "H19" and "IGF2". In 10% of the cases the syndrome is associated with maternal uniparental disomy (UPD) on chromosome 7. This is an imprinting error where the person receives two copies of chromosome 7 from the mother (maternally inherited) rather than one from each parent.

Like other imprinting disorders (e.g. Prader–Willi syndrome, Angelman syndrome, and Beckwith–Wiedemann syndrome), Silver–Russell syndrome may be associated with the use of assisted reproductive technologies such as in vitro fertilization.

Most patients recover completely within 1–2 months.

However many reported cases have lasted 18–24 months and longer.

The cause of PVS is unknown; however, genetic factors and nutritional deficiencies may play a role. It is more common in women, particularly in middle age (peak age is over 50). In these patients, esophageal squamous cell carcinoma risk is increased; therefore, it is considered a premalignant process.

The condition is associated with koilonychia, glossitis, inflammation of the lips (cheilitis), and splenomegaly.

Esophageal web in Plummer-Vinson syndrome is found at upper end of esophagus(post cricoid region) and Schatzki ring may be found at the lower end of esophagus.

There is risk of perforation of the esophagus with the use of dilators for treatment. Furthermore, it is one of the risk factors for developing squamous cell carcinoma of the oral cavity, esophagus, and hypopharynx.