Although evaluation of an abdominal mass often occurs in an outpatient setting, pediatric hospitalists are often asked to expedite the initial assessment and coordinate the appropriate consultations. The diagnostic possibilities vary considerably, based on the patient’s age and associated symptoms. The most urgent considerations are acute surgical conditions and neoplasms. A careful history and physical examination should guide a directed laboratory and imaging evaluation, leading to the diagnosis.

There are many structures within the abdomen from which masses can arise (Table 16-1). Abdominal masses can represent abnormal tissue mass of a solid organ such as the liver, spleen, or kidney or abnormal filling of a viscous organ such as the bowel or bladder. The most common source of an abdominal mass besides constipation is kidney pathology.

Abdominal masses present in two distinct ways: painless or with abdominal symptoms. A painless mass is the classic sign of abdominal malignancy, particularly Wilms tumor and neuroblastoma. However, painless masses may also be completely benign, such as a fecal mass in a constipated child, a horseshoe kidney, or a wandering spleen. Painless masses are usually identified incidentally, often by parents when bathing the child, and sometimes on routine physical examinations. Systemic symptoms such as weight loss, pallor, bruising, or bleeding are suggestive of a malignant process. Diarrhea can be a sign of a vasoactive secreting tumor, while hematuria strongly suggests renal involvement. Masses may cause or be the result of GI obstruction and can present with vomiting, abdominal pain, and constipation. Masses that are renal in origin can present with symptoms of urinary dysfunction and hematuria. Painful masses require an evaluation for possible urgent intervention for ischemic diseases like ovarian torsion or intussusception or the need for decompression of the bowel or bladder. Duration of the symptoms is an important consideration. Slowly growing masses are typical of some malignancies, while rapidly enlarging masses are more typical of others. Chronic abdominal pain and abnormal bowel habits may point to constipation. Periodic pain may point to a recurrent process, either acutely, as in intussusception, or chronically, such as a volvulus.

Age is an important factor to consider. Neonates can present with congenital anomalies such as cystic kidneys. Neuroblastomas and storage diseases typically present younger than 2 years old. Wilms tumors and other malignancies are more common in older children. Certain syndromes are at increased risk of Wilms tumors, such as Beckwith-Wiedemann.

A thorough physical examination will help determine the source of the mass. Tenderness will confirm the report of pain, and rebound tenderness indicates a more severe and acute process that has evolved into peritonitis. Localization of the mass aids the differential diagnosis.

The abdomen is classically divided in four quadrants. The right upper quadrant contains the liver, gallbladder, and bowel. The liver is often palpated under the costal margin, and up to 2 to 3 cm below in infants. The liver may be displaced inferiorly with hyperaeration of the chest cavity. When the liver edge extends to the left of the midline, it is likely enlarged. Extreme hepatomegaly that extends to the right lower quadrant can be missed because the liver edge is not palpable anywhere in the right upper quadrant. The left upper quadrant contains the spleen, pancreas, stomach, and bowel. The spleen is a mobile structure so that palpation of a mildly enlarged spleen tip may move it beyond the tactile sensation of the following examiner. Both the right lower quadrant and the left lower quadrant contain bowel and the female reproductive organs. Aside from the liver, these intraperitoneal structures are not typically palpable. In young infants the bladder may be palpable in the suprapubic area, but this structure becomes intrapelvic in later infancy. Retroperitoneal structures, such as the aorta and kidneys, are not normally palpable. Normal structures may be felt in patients who are very thin and have relaxed abdominal musculature, especially the aorta, which can be appreciated as a pulsatile midline structure, and the tip of the spleen in the left upper quadrant.