causes of bleeding that are not directly due to trauma). Blood can escape from blood vessels as a result of 3 basic patterns of injury:
Intravascular changes – changes of the blood within vessels (e.g. ↑ blood pressure, ↓ clotting factors)
Intramural changes – changes arising within the walls of blood vessels (e.g. aneurysms, dissections, AVMs, vasculitides)
Extravascular changes – changes arising outside blood vessels (e.g. H pylori infection, brain abscess, brain tumor)The underlying scientific basis for blood clotting and hemostasis is discussed in detail in the articles, coagulation, hemostasis and related articles. The discussion here is limited to the common practical aspects of blood clot formation which manifest as bleeding. Some medical conditions can also make patients susceptible to bleeding. These are conditions that affect the normal hemostatic (bleeding-control) functions of the body. Such conditions either are, or cause, bleeding diatheses. Hemostasis involves several components. The main components of the hemostatic system include platelets and the coagulation system. Platelets are small blood components that form a plug in the blood vessel wall that stops bleeding. Platelets also produce a variety of substances that stimulate the production of a blood clot. One of the most common causes of increased bleeding risk is exposure to nonsteroidal anti-inflammatory drugs (NSAIDs). The prototype for these drugs is aspirin, which inhibits the production of thromboxane. NSAIDs inhibit the activation of platelets, and thereby increase the risk of bleeding. The effect of aspirin is irreversible; therefore, the inhibitory effect of aspirin is present until the platelets have been replaced (about ten days).
A gangliocytic paraganglioma  is a rare tumour that is typically found in the duodenum and consists of three components: (1) ganglion cells, (2) epithelioid cells (paraganglioma-like) and, (3) spindle cells (schwannoma-like). Symptoms and signs
The most common presentation is gastrointestinal bleed (~45% of cases), followed by abdominal pain (~43% of cases) and anemia (~15% of cases). Pathology
GP consist of three components (1) ganglion cells, (2) epithelioid cells (neuroendocrine-like), and (3) spindle cells (schwannoma-like). The microscopic differential diagnosis includes poorly differentiated carcinoma, neuroendocrine tumour and paraganglioma.GPs may be sporadic or arise in the context neurofibromatosis type 1. See also
Schwannoma
Paraganglioma


== References ==