An abdominal mass can be observed during a physical examination in a myriad of conditions, but it is imperative to determine its location, size, shape and the presence of other accompanying signs. A thorough workup, primarily through imaging studies and biopsy, is pivotal to define the underlying cause.
An abdominal mass is a constitutive feature of numerous autoimmune, infectious, malignant and congenital disorders, which is why its characteristics can narrow the differential diagnosis. Upon inspection, localization should be defined first, as masses in the right-upper quadrant are indicative of hepatobiliary tract disorders, such as cholecystitis and tumors of the liver and gallbladder, while pancreatic abscesses and pseudocysts, but also malignancies of the pancreas and stomach can present as a mass in the epigastric area . On the other hand, lesions of the female reproductive tract (ovarian cysts, uterine myomas), diverticulitis are associated with a mass in the lower quadrants of the abdomen  . Finally, masses in the flank area are highly indicative of kidney-related pathology. In fact, more than half of all abdominal masses in the pediatric population stem from kidney diseases, including malignancies (Wilms' tumor, neuroblastoma), polycystic kidney disease (PKD), hydronephrosis and the presence of an ectopic kidney . One of the most important conditions that can be recognized with a simple palpation of an abdominal mass is an aneurysm of the abdominal aorta (AAA), in which a pulsatile mass in the umbilical area is a highly specific finding . Apart from its location, it is important to note its consistency, fluctuation, and presence of accompanying symptoms. Fever, hematuria, weight loss, fatigue, abdominal pain, diarrhea, constipation, jaundice, dysmenorrhea, overlying skin lesions and hypotension can all be encountered, depending on the underlying cause  .
A detailed patient history and a thorough physical examination can reveal key information about the underlying cause, and they must be pointed out as essential parts of the diagnostic workup. As mentioned previously, the location, size, consistency, mobility, as well as characteristics of edges and the surface can help in assuming the organs or tissues from which the mass originates, while basic patient information (age, gender) and a meticulously obtained history of present illness can further support the presumed diagnosis. If additional symptoms are presents, such as fever, hematuria, jaundice, etc, laboratory studies comprised of a complete blood count (CBC), urinalysis, liver and kidney function tests, as well as inflammatory markers test (C-reactive protein, erythrocyte sedimentation rate and fibrinogen) are necessary  . Imaging studies, however, are the cornerstone of evaluating an abdominal mass and several procedures may be implemented. Ultrasonography can be performed as an initial procedure to examine the kidneys, liver, spleen, and the reproductive organs, while computed tomography (CT) and magnetic resonance imaging (MRI) are recommended if the cause remains unknown, especially if gastrointestinal (eg. gallbladder or intestinal perforation) or vascular (AAA) pathology is suspected   . In some cases, excision of the mass or biopsy can be indicated to confirm the etiology.
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