Abdominal Masses – IMAGING

Abdominal masses in a child are source of concern to the parent, as well as the paediatrician, and present a diagnostic challenge. A radiologist plays a pivotal role in the diagnostic workup. Enlarged organs constitute 57% of abdominal masses in the infants and children, but the main thrust of imaging studies in childhood abdominal masses is directed towards pathological masses other than diffuse organomegaly. In general, 90% of such abdominal masses in infants and children are retroperitoneal of pelvic and half of these are related to urinary tract.
Irrespective of anatomical location of the abdominal masses and age of the child, the plain film radiography forms the primary imaging modality. Dilated bowel loops, which may simulate a mass, can be easily detected on plain film. The underlying cause may also be evident either on the plain film itself or a directed contrast examination. Other findings on the plain film which may aid in the diagnosis of an abdominal mass are displacement of adjacent bowel loops due to a soft tissue density, presence of calcification and its nature, associated bony abnormalities like congenital defects, metastasis, or direct invasion by a tumour mass.
Abdominal sonography forms the next important imaging modality, speciality if a gastrointestinal origin is not suspected. Sonography helps differentiate retroperitoneal form intraperitoneal masses and solid from cystic masses. Further diagnostic work is based on the information, obtained at plain film and ultrasonography. However, a selective and caring approach is mandatory, in order to limit the radiation hazards and for cost effectiveness.
Intravenous urography was a routine and essential part of diagnostic armamentarium in the work-up of a child with abdominal masses until recent past. With the advent of cross-sectional imaging techniques, the use of IVU has become more judicious, being needed only when a mass in renal region is suspected at plain film and/or ultrasonography needs further evaluation. IVU provides information regarding the functional status of the kidneys, and the effect of the mass on its position, outline and pelvicalyceal system.
Computerized Tomography (CT) is an excellent cross-sectional imaging technique in abdominal masses due to the explicit anatomical details. It helps assess the exact size and extent of the mass, thereby allowing accurate staging, which is a prerequisite to a successful management in childhood malignancies. Involvement of major blood vessels by dynamic CT following intravenous contrast administration is an added advantage. However, it has limitation in children, in addition to the radiation involved, the relative paucity of fat in children may result in images which may be difficult to interpret.
MRI, especially with the advent of short scan time and open type magnets, is a very promising modality although long-term results are still awaited in imaging of paediatric abdominal masses. Use of angiography is now limited to providing a road map prior to surgery for the hepatic tumours or when a partial nephrectomy is being contemplated. Radioisotope scans have limited role. It may be diagnostic in haemangioendothelioma, choledochal cyst, biliary atresia and helps distinguishing between a UPJ obstruction and a congenital multi-cystic dysplastic kidney.
Abdominal masses can be divided into three major groups in paediatric age:
Retroperitoneal (which may be renal, or extrarenal), Hepatobiliary and Gastrointestinal. Retroperitoneal masses constitute the great majority of abdominal masses in children and most are renal in origin e.g., hydronephrotic kidney, multicystic dysplastic kidney, polycystic kidney, nephroblastoma, mesoblastic nephroma, renal vein thrombosis etc. Characteristic findings of some of the important and commonly met childhood masses are as follows:

Staging is done at CT
• Stage I – Tumour limited to kidney; capsule intact.
• Stage II – Tumour extends beyond the kidney into perineal soft tissues; vessels outside kidney substance infiltrated or contain tumour thrombus.
• Stage III – Non-haematogenous tumour confined to abdomen: (i) Lymph nodes in renal hilum, periaortic or beyond, (ii) implants on peritoneal surfaces.
• Stage IV – Haematogenous metastases e.g., lung, liver, bone and brain.
• Stage V – Bilateral renal involvement at diagnosis.
Retroperitoneal tumours of non-renal origin are neuroblastoma, teratoma, adrenal haemorrhage, etc.

Hepatobiliary masses constitute approx 6% of all childhood abdominal masses.

• Choledochal Cyst: About 40-60% present before 10 years of age. Most commonly present with obstructive jaundice. Can develop complications like stones in up to 70% cases, pancreatitis, rupture or neoplasia. USG is the imaging modality of choice. It shows focal dilatation of CBD with sparing of IHBR.
CT helps to differentiate from intrahepatic cysts:
• Infantile Haemangioendothelioma: Usually well-defined but has varying picture on USG.
• Hepatoblastoma: It was seen most commonly in boys < 3 years. Plain film shows hepatomegaly ± calcification ± infiltration or compression of hepatic vasculature. CT scan further helps.
• Hamartoma: Hamartoma accounts for 22% of benign liver tumours in childhood. A multi-septated cystic mass is seen at USG or CT.
• Hepatic Abscess: These can be hematogenous, biliary, post-traumatic or post-surgical in origin. At USG these are seen as hypoechoic masses. At CT, these are seen as hypoattennuating rim enhancing lesions.
Among the masses of GI origin, duplication cysts, pancreatic masses and lymphomatous masses are of great importance.

• Duplication Cyst of Intestinal Tract: Frequent location is terminal ileum and ileocaecal valve. Others are oesophagus, stomach and duodenum.
Plain film shows mass effect with calcification in wall. Ultrasound shows an anechoic cystic mass. Barium study may demonstrate lumen of communicating duplications and mass effect.
• Omental and Mesenteric Cysts: 50% are located in mesentery of small bowel. USG shows a cystic mass. CT reveals a low attenuation mass.
• Ovarian Masses: Mature teratoma: Most common benign lesion (40-50%). At USG it is cystic/solid/complex in appearance. Malignant ovarian lesions are rare and appear as solid lesion on USG/CT.
• Hydrocolpos: USG shows a large midline cystic structure consistent with distended vagina and uterus, with scattered internal echoes.

Although the imaging investigations have to be tailored according to the individual cases, but a strategy has to be formulated by each paediatric radiology centre, based on the facilities available and their health care policies.

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