During the prefibrotic phase, injury to endothelial cells secondary to radiation causes destruction of local vasculature, and recruitment of inflammatory cells and fibroblasts via pro-inflammatory cytokines like TNF-α, FGF-β and TGF-β1. In addition, osteoblasts within the bone are damaged and destroyed, leading to decreased production of normal bone tissue. In the constitutive organized phase, fibroblasts persist and are converted to myofibroblasts by these same cytokines, that begin to fibrous extracellular matrix (ECM) within the affected bone. Consequently, the increased production of ECM by myofibroblasts coupled with decreased production of osteoid by osteoblasts results in weakened bony tissue. Finally, during the late fibroatrophic phase, the affected bone becomes hypocellular as myofibroblasts begin to die and leave behind weak, fibrotic tissue. Ultimately, these tissues are fragile and susceptible to damage by trauma or infection with little ability to repair or defend themselves due to the lack of vasculature caused during the pre-fibrotic phase. Given this understanding of the pathophysiology of ORN, current treatments are targeted at decreasing inflammatory cytokines and reducing free radical damage to DNA. Risk factors
Risk factors for osteoradionecrosis include:

Size and location of tumor; the risk of developing ORN increases with larger tumors, since they require higher doses of radiation to achieve cure, subsequently exposing nearby tissues to higher doses. While radiation therapy has become more targeted and precise, patients with tumors located closer to the mandible (e.g. oral cavity) or maxilla (e.g. nasopharynx) will more commonly develop ORN since the bone is more likely fall within the radiation field.
Gastric outlet obstruction (GOO) is a medical condition where there is an obstruction at the level of the pylorus, which is the outlet of the stomach. Individuals with gastric outlet obstruction will often have recurrent vomiting of food that has accumulated in the stomach, but which cannot pass into the small intestine due to the obstruction. The stomach often dilates to accommodate food intake and secretions. Causes of gastric outlet obstruction include both benign causes (such as peptic ulcer disease affecting the area around the pylorus), as well as malignant causes, such as gastric cancer. Causation related to ulcers may involve severe pain which the patient may interpret as a heart condition/attack.Treatment of the condition depends upon the underlying cause; it can involve antibiotic treatment when Helicobacter pylori is related to an ulcer,  endoscopic therapies (such as dilation of the obstruction with balloons or the placement of self expandable metallic stents), other medical therapies, or surgery to resolve the obstruction. Signs and symptoms
The main symptom is vomiting, which typically occurs after meals, of undigested food devoid of any bile. A history of previous peptic ulcers and loss of weight is not uncommon. In advanced cases, signs to look for on physical examination are wasting and dehydration. Visible peristalsis from left to right may be present. Succussion splash is a splash-like sound heard over the stomach in the left upper quadrant of the abdomen on shaking the patient, with or without the stethoscope.