Ultrasound and alternative multimodality imaging of intra-abdominal and pelvic cystic masses in the newborn

Abstract

Introduction: Ultrasound is used commonly to detect and diagnose intra-abdominal and pelvic cystic masses in the newborn as it is easily available, relatively low cost, and non-invasive. Discussion: The diagnosis can be made or narrowed down by determining the location, size, sonographic features, organ involvement, and internal vascularity. The differential diagnoses include hydronephrosis, multicystic dysplastic kidney, adrenal haemorrhage, cystic teratomas, ovarian cysts, enteric cysts, meconium cysts, and liver haemangiomas. With the appropriate radiological knowledge, the ultrasound practitioner can help obtain an accurate diagnosis. Conclusion: This pictorial essay will familiarise the reader with the different common causes of intra-abdominal and pelvic masses detected on ultrasound through a wide range of conditions. The role of ultrasound in the evaluation of these conditions will be discussed and alternative imaging correlates will be offered.

Introduction

Ultrasound is used commonly as a diagnostic tool in the paediatric population to investigate intra-abdominal and pelvic pathology as it is accessible, low cost, and non-invasive. In addition, high-resolution images can be obtained without the need for ionizing radiation and sedation. It is often the first radiological investigation performed for asymptomatic palpable abdominal masses when a child presents with symptoms related to the mass or as workup for an abdominal mass detected on a prior antenatal ultrasound.

When intra-abdominal and pelvic cystic masses are detected on ultrasound, the diagnosis can be made or narrowed down by determining the location, size, sonographic features, organ involvement, and internal vascularity.^1–3 The differential diagnoses include hydronephrosis, multicystic dysplastic kidney, adrenal haemorrhage, cystic teratomas, ovarian cysts, enteric cysts, meconium cysts, and liver haemangiomas. With appropriate radiological knowledge, an ultrasound practitioner can help in obtaining the diagnosis for the patient, hence, allow expedient and correct clinical management.

We aim to familiarise the reader with the different common causes of intra-abdominal and pelvic masses detected on ultrasound. In addition, through understanding the clinical presentation and the use of other supporting diagnostic imaging modalities, we discuss how a specific diagnosis can often be made.

Haemangiomas

Hepatic haemangiomas are the most common benign hepatic tumour of infancy ⁴ (Figures 1 and 2). There are two types: infantile hepatic haemangiomas (IHH) and congenital hepatic haemangiomas (CHH). IHHs have a typical course in which they appear within the first few weeks of life, undergo proliferation during the first few months, and gradually involute over the next few years, probably due to thrombosis and scar formation. About 85% of patients present by the age of six months with symptoms such as a palpable abdominal mass, hepatomegaly, congestive heart failure, thrombocytopenia, and rarely, rupture with resultant haemoperitoneum.^5,6 In about 50% of cases, these patients also have cutaneous haemangiomas. IHHs are usually multifocal, diffuse, and uncommonly present as a solitary lesion within the liver.^5,6 The multifocal nodular pattern of infiltration is usually seen in the early stages, with nodules ranging in size from 0.5 cm to 12 cm. Over time, the lesions, which tend to be peripheral and adjacent to the capsule, grow and coalesce into a large confluent mass (diffuse involvement). In the later stages, liver capsular retraction secondary to fibrotic change and compensatory hypertrophy of the unaffected liver segments may be observed.

Figure 1.

Hepatic haemangioma. (a) This abdominal ultrasound in a 23-day-old neonate showed a large right hepatic lobe heterogeneous cystic mass with septa (white arrow). (b) Colour Doppler ultrasound demonstrated a hypovascular mass (white arrow) with flow around its perimeter.

Figure 2.

Hepatic haemangioma. The subsequent (a) axial and (b) coronal contrast-enhanced CT images showed a relatively hypovascular mass with nodular peripheral enhancement (white arrows). This was diagnosed on imaging to be an infantile hepatic haemangioma and the patient was treated with propranolol. Subsequent ultrasounds showed a gradual decrease in size of the infantile hepatic haemangioma.

CHHs are usually detected prenatally, fully formed at birth and, unlike IHHs, tend to present as a solitary mass in the newborn. ⁴ They tend to then undergo varying degrees of involution. Like IHHs, they can also present with thrombocytopenia and congestive heart failure.

Ultrasound is a commonly used modality to image hepatic haemangiomas. On ultrasound, IHHs are often seen as discrete multifocal cystic lesions that are well-defined, uniform, and circumscribed or as heterogeneous echotexture of the liver in regions of extensive diffuse involvement. The cystic lesions are usually hypoechoic relative to the hepatic parenchyma but when it progresses to a confluent mass it can be hyperechoic or isoechoic to the liver. Doppler vascularity is usually variable. CHHs, on the other hand, are described on ultrasound as large, well-circumscribed heterogeneous lesions due to the presence of haemorrhage, necrosis, fibrosis, and/or calcification.

Dynamic post-contrast magnetic resonance (MR) imaging allows for further characterization and they typically show early peripheral enhancement, confirming the diagnosis. ⁴

The other main differential diagnosis of neonatal cystic liver masses would include mesenchymal hamartomas and hepatoblastomas. Mesenchymal hamartomas are the second most common benign hepatic tumour after hepatic haemangioma. They are predominantly cystic but can also be partially or completely solid. On ultrasound, although some of their imaging features overlap with hepatic haemangiomas, they are not hypervascular on colour Doppler. Hepatoblastomas tend to occur in the young infant rather than the newborn. On ultrasound, they are distinguished by their enhancement pattern which tends to be heterogeneous rather than centripetal. In addition, more than 90% of patients will show an elevated serum alpha-fetoprotein, which is rarely elevated in hepatic haemangiomas. ⁷

Adrenal haemorrhage

Adrenal haematomas (Figures 3 and 4) are the most common cause of an adrenal mass in a neonate, usually presenting in the first few days of life.^8,9 Around 10% of adrenal haemorrhage cases are bilateral and 70% are right unilateral. Often there is a history of a difficult delivery, sepsis, perinatal hypoxia, bleeding diathesis, or abdominal trauma. Clinical presentations can present as anaemia, abdominal pain, or hemodynamic instability. Severe bilateral adrenal haemorrhage can occur in Waterhouse–Friderichsen syndrome, which may result in adrenal insufficiency. ¹⁰

Figure 3.

Adrenal haemorrhage. (a) A newborn presented with a history of prior intracranial bleed and pallor. The ultrasound was performed to look for a potential source of the intra-abdominal bleed. A mixed solid-cystic mass in the right suprarenal region, inseparable from the right adrenal gland was seen. (b) No flow was demonstrated within this mass on colour Doppler. It likely represented an adrenal haematoma.

Figure 4.

Adrenal haemorrhage. Subsequent T1-weighted MR (a) coronal and (b) axial showed a high T1-weighted mass at the suprarenal region, compatible with an adrenal haematoma (white arrows). This completely resolved with conservative management on subsequent ultrasound follow-up.

Serial ultrasound remains the first-line investigation for the evaluation of adrenal haemorrhage. On ultrasound, it can appear as a cystic mass in the suprarenal region. Accurate localization of the mass to the suprarenal region is critical as a large intrathoracic mass can be mistaken for a suprarenal mass. ¹¹ This can be done by tracing the relations of the mass to the hemidiaphragm and noting the presence of surrounding pleural fluid. A mass below the hemidiaphragm that is not surrounded by pleural fluid is suprarenal in location. Acutely, it presents as an isoechoic to slightly hyperechoic well-defined mass which can be homogeneous or heterogeneous. It is avascular and involves a part or whole of the adrenal gland. Over time, it will undergo cystic transformation and involution, becoming completely cystic. ¹² The haemorrhage can also calcify and will show punctate or curvilinear areas of echogenicity. Eventually, it will completely resolve and resume a normal appearance.

The other main differential diagnosis of neonatal cystic adrenal masses would be a neuroblastoma which can show similar radiological features in 50% of cases. ¹² Hence, follow-up ultrasounds are recommended to monitor for interval resolution. Neuroblastomas frequently calcify, are poorly encapsulated, and tend to encase the retroperitoneal vessels. However, ultrasound remains inferior to both computed tomography (CT) and MR imaging to assess for neuroblastoma and its extent. ¹³

Hydronephrosis

Hydronephrosis (Figures 5 and 6) is the most common cause of an intra-abdominal mass in the newborn.^1,14 It can also present with symptoms of obstruction such as recurrent urinary tract infections or haematuria. Of note, hydronephrosis is often first detected on a prior antenatal ultrasound. On ultrasound, hydronephrosis is characterized by a dilated renal pelvis and renal calyces with accurate depiction of these structures playing an important role in differentiating hydronephrosis from true cystic renal lesions.

Figure 5.

Hydronephrosis. Ultrasound of a newborn for investigation of abdominal distension. (a) Longitudinal, (b) transverse, and (c) colour Doppler ultrasound images were obtained showing a severely dilated right kidney with thinning of the renal cortex (white arrows) and absence of internal vascularity. The level of obstruction could not be ascertained by ultrasound.

Figure 6.

Hydronephrosis. A subsequent MR abdomen was performed. (a) Coronal and (b) axial T2-weighted images confirmed the presence of a severely dilated right kidney secondary to pelvic-ureteric junction obstruction. Here the thinning of the renal cortex (outlined white arrows) and dilated renal pelvis (white arrows) was demonstrated.

The causes of hydronephrosis include transient hydronephrosis (41–88%), ureteropelvic junction obstruction (10–30%), vesicoureteral junction obstruction (10–20%), ureterovesical junction obstruction (5–10%), multicystic dysplastic kidney (4–6%), duplex kidney/ureterocoele (5–7%), posterior urethral valve/urethral atresia (1–2%), prune belly syndrome, cystic kidney disease, and congenital ureteric strictures. ¹⁵

Transient hydronephrosis is by far the most common cause of hydronephrosis, as mentioned above. The aetiology is not certain but may due to immature or poor peristalsis of the smooth muscle of the renal pelvis leading to poor emptying and urinary stasis in the renal pelvis. Resolution of the hydronephrosis usually occurs within the first few years of life and the time to resolution usually depends on the initial severity. It is impossible to differentiate between transient hydronephrosis and ureteropelvic junction obstruction on a single ultrasound examination, hence, serial follow-up ultrasounds are suggested until a complete resolution.

Ureteropelvic junction obstruction is either a functional or anatomic obstruction of urine flow at the ureteropelvic junction. The causes are divided into intrinsic and extrinsic causes. Intrinsic causes include abnormal development of ureteral smooth muscle and resultant aperistalsis, fibrous bands, folds, or valves. Extrinsic causes include variant vessels crossing the upper ureter and pelvis with resultant ureteropelvic junction obstruction. On ultrasound, features of hydronephrosis which are a dilated renal pelvis in communication with multiple dilated calyces should be seen. In addition, there is abrupt narrowing at the ureteropelvic junction and absence of a dilated ureter downstream. Often, in severe cases, there is renal parenchymal thinning.

Technitium99m-MAG3 (mercaptoacetyltriglycine) renography is used to further evaluate the obstruction, in which the findings would be the lack of drainage from the dilated renal pelvis despite the use of diuretics and hydration. ¹

Multicystic dysplastic kidney

Multicystic dysplastic kidney (MCDK) (Figure 7) is due to abnormal or incomplete kidney development resulting in a non-functioning kidney.^3,16 It is thought to arise either from abnormal ureteric budding during embryogenesis or from severe collecting system obstruction. ¹⁷ It is the second most common cause of renal tract abnormalities detected in the prenatal period after hydronephrosis. MCDK involvement is usually unilateral and is often first diagnosed on antenatal screening ultrasound. If there is bilateral renal involvement, it is incompatible with extrauterine life. Occasionally, MCDK is diagnosed after birth when a newborn undergoes investigation for reasons such as assessment of the renal tract for congenital abnormalities or for a palpable abdominal mass. Of note, many of the MCDKs undergo spontaneous involution in the antenatal period and can present as unilateral renal agenesis.

Figure 7.

Multicystic dysplastic kidney. (a) Ultrasound on a newborn with known imperforate anus to look for congenital abnormalities. A normal right kidney could not be seen. Instead, there was a reniform shaped lesion with multiple cysts (largest measuring 2.9 × 1.5 × 1.3 cm) in the right side of the abdomen (white arrow). The left kidney was normal. These findings were suggestive for a right multicystic dysplastic kidney. In addition, the distal end of the rectum was not visualized and was approximately 1.8 cm from the anus. This likely represented a high anorectal malformation. (b) A subsequent Technitium99m-MAG3 renography was performed which showed a complete lack of flow and excretion within the right kidney, compatible with a multicystic dysplastic kidney.

The majority of MCDKs are sporadic in nature with no genetic explanation. In some cases, MCKD is part of a generalized disorder such as the VATER association (vertebral defects, imperforate anus, tracheoesophageal fistula, radial, and renal dysplasia), Zellweger syndrome, or the BOR (branchio-oto-renal) syndrome. ¹⁸ Approximately 20–50% of patients with multicystic dysplastic kidney also have a concomitant contralateral renal abnormality, including vesicoureteral reflux, UPJ obstruction, and primary megaureter. ¹

On ultrasound, there are multiple cysts of varying sizes and, in most cases, they do not communicate with one another. Sometimes, these cysts are separated by a small amount of dysplastic renal parenchyma. However, in the hydronephrotic form, the cysts have been reported to communicate and can be mistaken for a hydronephrotic kidney. ¹⁷ Ultrasound plays a vital role in guiding the management and surveillance of MCKD, ¹⁹ starting from the antenatal period where most MCKD is detected. Ultrasound surveillance may be sufficient as to make the diagnosis, although sometimes the use of voiding cystourethrogram to exclude reflux may be considered. Functional imaging to demonstrate lack of renal function still has a role.

Duplication cysts

Enteric intestinal duplications are rare congenital anomalies that can occur anywhere in the gastrointestinal tract (Figures 8 and 9). Duplication cysts most commonly occur in the distal ileum followed by the oesophagus, colon, jejunum, stomach, and duodenum. ²⁰ They should have an intimate attachment to the gastrointestinal tract, contain a layer of smooth muscle in the wall, and have an epithelial lining resembling some part of the gastrointestinal tract. They can contain heterotopic tissue including gastric mucosa, pancreas, and lymphoid tissue. They are usually asymptomatic. However, complications do occur, and they include obstruction by volvulus or intussusception, bleeding, infection, and perforation.

Figure 8.

Enteric cyst. Screening ultrasound of a 36-week premature infant. (a, b) Transverse views showed two cystic structures in the left hypochondrium, posterior to the stomach. The larger lesion measured 2.1 × 1.9 × 1.4 cm and the smaller one was 1.9 × 1.2 × 0.9 cm. These structures were intraperitoneal and were inseparable from the stomach. However, they were separate from the spleen, adrenal, and pancreas. There was no vascularity, solid component, or calcification within these cysts. In one, there was an echogenic inner layer (outlined black arrow) representing the mucosa and submucosa, and an outer hypoechoic layer (outlined white arrow) representing the muscularis propria. This represented the classical muscular rim sign or double-wall sign seen commonly in enteric duplication cysts and is known as the ‘gut signature’.

Figure 9.

Enteric cyst. A subsequent MR abdomen was performed for further evaluation. (a) Coronal T2-weighted, (b) axial T2-weighted images confirmed the presence of high T2-weighted cystic structures (outlined white arrows) arising from the stomach. (c) Post contrast T1-weighted axial images demonstrated no solid component or wall enhancement of these cystic lesions (outlined white arrows). These MR findings confirmed the diagnosis of gastric enteric duplication cysts.

On ultrasound, they are cystic structures inseparable from the adjacent gastrointestinal tract. They can appear round or tubular and have a distinct gut signature called the muscular rim or double-wall sign, although this is not pathognomonic. ²¹ The echogenic inner layer of the cyst represents the mucosa and submucosa, and an outer hypoechoic layer represents the muscularis propria. Less often, five sonographic layers are identified, reflecting superficial mucosa, deep mucosa, submucosa, muscularis propria, and serosa, which increases the specificity in making the sonographic diagnosis of an enteric duplication cyst. ²¹

Meconium cysts

Meconium pseudocysts (Figures 10 and 11) are pseudocysts that form as a fibrotic walling off reaction secondary to meconium peritonitis.^3,22 Meconium peritonitis is due to in-utero bowel perforation which is secondary to in-utero bowel obstruction and may be caused by segmental atresia, cystic fibrosis, microcolon, or volvulus but often there is no clinically apparent cause.

Figure 10.

Meconium cyst. A 35-week premature infant presented with an intra-abdominal mass. (a) Longitudinal ultrasound and (b) power Doppler images of the abdomen. A huge cystic mass was occupying most of the abdomen. It was ill-defined with some peripheral curvilinear calcification (outlined white arrows). No solid component or internal vascularity was seen within it. Some septa were seen within the mass as well as layering of echogenicity indicating a fluid-debris level. The abdominal solid organs, although displaced by the mass, appeared unremarkable.

Figure 11.

Meconium cyst. Abdominal radiograph demonstrated a large radiopaque mass (outlined black arrow) in the abdomen with curvilinear rim calcification (white arrows). These findings together with the clinical history suggested a large multiloculated cystic mass with calcification and septation, likely representing a meconium cyst, which was confirmed during surgery.

Patients are often diagnosed in the antenatal period. This may be clinically asymptomatic until the postnatal period, in which case, the patient will present with abdominal distension or persistent vomiting. Large cysts can also be associated with diaphragmatic elevation and secondary ventilatory failure.

On postnatal ultrasound, a cystic mass with echogenic contents and echogenic walls which may contain calcific foci is seen.^3,22 Scattered foci of intraperitoneal calcification may also be detected on ultrasound. These findings together with a clinical history of prematurity often allow a confident imaging diagnosis of meconium cyst. If intraluminal gas is present, it indicates that there is persistent communication between the cyst cavity and the lumen of the perforated bowel after birth.

The use of plain abdominal radiography and both upper and lower gastrointestinal tract barium studies can be used to confirm the presence of peritoneal calcification and to look for occult perforations.

Ovarian cysts

Ovarian cysts (Figure 12) are the most common abdominal mass in the female neonate. ²³ They are thought to form due to fetal exposure to maternal gonadotrophins. The maternal risk factors would include diabetes mellitus, Rh isoimmunization, and toxaemia. These cysts are benign functional ovarian cysts which gradually increase in size during the third trimester and neonatal period. They include follicular cysts, theca lutein cysts, corpus luteum cysts, and simple cysts. Most of these cysts are unilocular, unilateral, and generally small (<2 cm). ²⁴ However, they can occasionally be complicated with debris, clot, septa, and echogenic walls. They may occasionally grow large (>5 cm) ²⁵ and are then more likely to suffer complications. Common complications would include torsion, rupture, haemorrhage, and compression of the adjacent organs. ²⁵ These cysts commonly spontaneously regress and are more frequently seen in smaller cysts, ²⁵ probably due to the discontinuation of maternal gonadotrophin secretion.

Figure 12.

Ovarian cyst. Ultrasound pelvis of a newborn. (a) Transverse and (b) longitudinal ultrasound images of a right adnexal cystic lesion (white arrow) adjacent to the lower pole of the right kidney and measuring 1.5 × 1.3 × 1.8 cm. It had slightly thickened walls and a thin internal septum. The walls were hypovascular, but the surrounding ovarian parenchyma demonstrated vascularity on (c) power Doppler. These findings were highly suggestive for a cyst of ovarian origin.

Serial ultrasound is important in guiding the management of ovarian cysts as simple cysts smaller than 4 cm can be managed conservatively. However, ovarian cysts greater than 5 cm should be managed surgically with minimally invasive laparoscopy with aspiration, marsupialization, cystectomy, or oophorectomy.^24,25

Cystic teratoma

Retroperitoneal cystic teratoma (Figures 13 to 15) is a very rare embryonic neoplasm that should contain at least two or more of the three germ cell layers in varying proportions.^26,27 It is more common in a female neonate. It is found typically in the pararenal location and can occur bilaterally. ²⁸

Figure 13.

Cystic teratoma. A patient with Down’s syndrome who had an abdominal cyst of 8.97 × 7.15 cm diagnosed antenatally. Subsequent postnatal abdominal ultrasound showed a 10.8 × 10.7 × 8.5 cm intra-abdominal mixed solid-cystic structure (white arrow) with septa and no internal vascularity in the left flank extending to the midline. There were also echoic areas with posterior acoustic shadowing likely due to calcification (outlined white arrow). The ovaries were initially not well seen.

Figure 14.

Cystic teratoma. The abdominal radiograph showed a left-sided large abdominal mass (white arrow) with internal calcifications (outlined black arrow) and displacement of the adjacent bowel.

Figure 15.

Cystic teratoma. MR (a) coronal T2-weighted, (b) axial T2-weighted fat-saturated, (c) axial T1-weighted, and (d) axial T1-weighted fat-saturated images showed a large retroperitoneal fat-containing mass (white arrows) situated in the left side of the abdomen causing bowel displacement. Marked decrease in signal in the fat containing areas was seen on the fat-saturated sequences. The diagnosis of a retroperitoneal cystic mature teratoma was confirmed at surgery. Follow-up ultrasounds after the operation showed the presence of bilateral normal ovaries. The patient was disease free at five years of age.

Ultrasound features are variable and do not provide reliable tissue differentiation, therefore often cross-sectional imaging would be required to attain the diagnosis. On ultrasound, it can appear as a predominantly cystic, solid, or a complex mass with specular echoes indicative of calcification and may have fat-fluid levels. ²⁹

Both CT and MR imaging can be used to distinguish the calcification, soft tissue, and adipose contents of the cystic teratoma as well as delineate the anatomic relationship to the adjacent organs and vascular structures. ³⁰ An abdominal radiograph can often be useful to distinguish a radiolucent mass which displaces the abdominal organs as well as demonstrates internal radiopaque calcification.

Conclusion

Ultrasound is used commonly for the investigation of abdominal and pelvic cystic masses in the newborn. The diagnosis is dependent on the technical expertise and experience of the operator; however, careful evaluation of precise location and features of the mass will allow narrowing of the differential diagnoses and even a specific diagnosis in some cases. Alternative imaging may be useful in equivocal cases.