Experimentally, local anaesthetic injections and tying of the arteries is reported to trigger the development of tissue changes similar to NS in lab rats. Factors which are thought to cause this ischemia are listed below, however sometimes there is no evident predisposing factor or initiating event. Trauma e.g. during intubation, or surgical procedures
Local anesthetic injection
Smoking
Alcohol
Diabetes mellitus
Vascular disease, (e.g. arteriosclerosis)
Pressure from a dental prosthesis
Allergy
Bulimia
Infection
Ionizing radiation

Diagnosis
Differentiation between this and SCC would be based on a history of recent trauma or dental treatment in the area. Immunohistochemistry may aid the diagnosis. If the lesion is NS, there will be focal to absent immunoreactivity for p53, low immunoreactivity for MIB1 (Ki-67), and the presence of 4A4/p63- and calponin-positive myoepithelial cells. Treatment
No surgery is required. Prognosis
Healing is prolonged, and usually takes 6–10 weeks. The ulcer heals by secondary intention. Epidemiology
The condition is rare. The typical age range of those affected by the condition is about 23–66 years of age. It usually occurs in smokers. The male to female ratio has been reported as 1.95:1, and 2.31:1. History
NS was first reported by Abrams et al. in 1973. Notes
References


== External links ==
One study suggests that simultanagnosia  may result from an extreme form of competition between objects which makes it difficult for attention to be disengaged from an object once it has been selected. Patients with simultanagnosia have a restricted spatial window of visual attention and cannot see more than one object at a time. They see their world in a patchy, spotty manner. Therefore, they pick out a single object, or even components of an individual object, without being able to see the global "big picture. "A study which directly tested the relationship between the restriction of the attentional window in simultanagnosia compared with the vision of healthy participants with normal limits of visual processing confirmed the limitations of difficulties of patients with simultanagnosia.There is considerable evidence that a persons cortex is essentially divided into two functional streams: an occipital-parietal-frontal pathway that processes "where" information and an occipital-temporal-frontal pathway that provides "what" information to the individual. Oculomotor apraxia
Bálint referred to this as "psychic paralysis of gaze"—the inability to voluntarily guide eye movements, changing to a new location of visual fixation. A major symptom of Oculomotor apraxia is that a person has no control over their eye movements, however, vertical eye movements are typically unaffected. For example, they often have difficulty moving their eyes in the desired direction. In other words, the saccades (rapid eye movements) are abnormal. Because of this, most patients with Oculomotor apraxia have to turn their heads in order to follow objects coming from their peripherals.