What is the role of CT in Wilms tumor imaging?

Updated: Mar 04, 2019
  • Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Eugene C Lin, MD  more...
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Answer

Abdominal CT scanning helps assess the origin of the tumor; lymph node involvement; bilateral renal involvement; and invasion into the renal vascular pedicle, IVC, and right atrium. In addition, scans depict hepatic and distant metastases. CT scan results (see the images below) help confirm that a tumor is in the kidney. Scans often show a surrounding rim of normal renal tissue, distortion of the renal collecting system, and medial displacement of the kidney. By comparison, a neuroblastoma (an important differential diagnosis) rarely distorts the renal collecting system and generally indents or displaces the kidney inferiorly or laterally. Hemorrhagic or cystic areas can be present, but they are not commonly seen. CT demonstrates mixed hypoattenuation with bands of enhancing tissue surrounding cystic and/or necrotic areas. If the rhabdoid variant is present, a CT scan of the head should be obtained to look for evidence of brain metastases. [10, 11, 12, 13, 15, 30, 31]

Unenhanced axial CT scans shows a 6 x 8 cm mass lo Unenhanced axial CT scans shows a 6 x 8 cm mass low attenuation mass arising from the lower pole of the right kidney and extending into the anterior renal cortex. Also note subtle unrelated medullary left renal nephrocalcinosis.
Enhanced axial CT scan shows a large solid tumor d Enhanced axial CT scan shows a large solid tumor displacing a rim of functioning cortical tissue posteriorly. Note also a second small low attenuation mass in the functioning cortex.
Axial and coronal reconstruction contrast-enhanced Axial and coronal reconstruction contrast-enhanced CT scan shows a fairly well defined left renal mass with a small central hypodense area due to central necrosis. Image courtesy Dr. Pedro Daltro and Dr. Edson Marchiori, Port Allegre, Brazil. edmarchiori@gmail.com
Unenhanced axial CT scans in the same patient as i Unenhanced axial CT scans in the same patient as in the previous image shows a large, solid mass with a heterogeneous mass in the right renal fossa crossing the midline and displacing the liver anteriorly. Image courtesy of Dr. Pedro Daltro and Dr. Edson Marchiori, Port Allegre, Brazil. edmarchiori@gmail.com
Contrast-enhanced axial CT scan in the same patien Contrast-enhanced axial CT scan in the same patient as in the previous images shows a large, solid mass with a heterogeneous mass with areas suggestive of necrosis. Note the normal functioning component of the right kidney. Image courtesy of Dr. Pedro Daltro and Dr. Edson Marchiori, Port Allegre, Brazil. edmarchiori@gmail.com

With CT and MRI, the use of intravenous contrast material is essential to assess both kidneys. The appropriate dose is 1 mL/0.5 kg body weight, with imaging at 65-70 seconds after the injection to allow the renal vein and the IVC to opacify. The section thickness varies with the capability of the machine being used.

CT helps identify a subgroup of patients with stage I disease who are at increased risk for having a pulmonary relapse. These children receive only single-agent chemotherapy. [30, 31] If findings on chest CT are positive while chest radiographic findings are negative, diagnostic biopsy of the lesions noted on the chest CT scan is recommended. In patients with large tumoral masses, nodal disease may be difficult to distinguish from the primary tumor. CT depicts the most common sites of tumoral spread—namely, the lymph nodes, lungs, and liver. However, CT scanning does not aid in determining whether the tumor can be removed, because this is accurately assessed only at the time of surgery.

Ritchey et al determined the accuracy of preoperative imaging in diagnosing bilateral Wilms tumors. [25] The authors examined case notes of 122 patients with synchronous bilateral Wilms tumors who were enrolled in the fourth National Wilms Tumor Study (NWTS-4). With the exception of one child, all patients underwent abdominal CT, MRI, or ultrasonography. The accuracy of each imaging modality was correlated with the size of the tumors. In 9 patients (7%), bilaterality was missed on the preoperative imaging studies. All but one of the missed lesions were small, 5 were greater than 1 cm, and 3 were 1-3 cm. CT was determined to be more sensitive than ultrasonography in detecting bilaterality. However, there was no single study that was able to depict more than 50% of lesions less than 1 cm in greatest dimension.


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