Trauma: This is the most common cause of bruising over the abdomen, resulting from direct blows to the abdominal area, which can be accidental or non-accidental (e.g., abuse). The mechanism of injury and the pattern of bruising can provide clues to the nature of the trauma.

Hematoma: A collection of blood outside of blood vessels, which can occur spontaneously or as a result of trauma. Abdominal hematomas can be due to various causes, including bleeding disorders or the use of anticoagulant medications.
Coagulopathy: Disorders that affect the blood's ability to clot, such as hemophilia, von Willebrand disease, or acquired conditions like liver disease or vitamin K deficiency, can lead to easy bruising, including over the abdomen.
Vascular Disorders: Conditions like vasculitis or telangiectasias can cause bruising due to inflammation or weakening of blood vessel walls.

Abdominal Aortic Aneurysm (AAA): Although less common, an expanding or ruptured AAA can cause abdominal bruising, especially if it involves the retroperitoneal space. This condition is life-threatening and requires immediate medical attention.
Bleeding from Internal Organs: Internal injuries or diseases (e.g., splenic rupture, liver laceration, or pancreatic pseudocyst) can cause bruising as blood tracks through tissues. These conditions can be life-threatening and may require surgical intervention.
Malignancy: Certain cancers, such as pancreatic cancer, can cause bruising due to tumor invasion into blood vessels or coagulopathy associated with malignancy.

Ehlers-Danlos Syndrome: A group of genetic disorders that affect connective tissues, leading to extremely flexible joints and very stretchy, fragile skin that bruises easily.
Scurvy: Vitamin C deficiency can lead to poor collagen synthesis, resulting in fragile blood vessels that can cause bruising, including over the abdomen.
Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, which can lead to bruising due to vascular fragility.