What is the role of MRI 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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In general, Wilms tumors have heterogeneously low signal intensity on T1-weighted MRIs and high signal intensity on T2-weighted MRIs. Hyperintense areas on T1-weighted images correspond with hemorrhage. A pseudocapsule is evident on T2-weighted imaging. MRI is not tissue specific. As with other cross-sectional imaging methods, tissue diagnosis is usually required with MRI. Signal intensity on MRIs does not help in distinguishing Wilms tumors from other solid renal tumors. Capsular invasion by a tumor can be missed. [13, 16, 32]

Wilms tumors typically appear inhomogeneous on gadolinium-enhanced images, whereas nephrogenic rests (which are sometimes precursors of Wilms tumors) appear as homogeneous masses. MRA may demonstrate the displacement of the renal vein and IVC, and it may aid in the diagnosis of thrombus of the renal vein of the IVC.

T1 and T2 prolongation is present. Capsular invasion is difficult to predict with imaging. However, CT and MRI are useful in demonstrating extension involving the IVC or tumoral thrombus. In addition, MRI has been used in screening for the nephrogenic rests of nephroblastomatosis and for multicentric Wilms tumors.

MRI may be useful in distinguishing between active nephrogenic rests or Wilms tumor from inactive nephrogenic rests. Information from T2-weighted MRIs is used to make this distinction; active nephrogenic rests and Wilms tumors are both hyperintense, whereas inactive nephrogenic (sclerotic) rests are hypointense. Overall sensitivities for detecting nephrogenic rests are 43% with nonenhanced images and 58% with contrast-enhanced images. Nephrogenic rests admixed with Wilms tumors less than 4 mm in diameter are not identified on MRIs. On gadolinium-enhanced T1-weighted images, Wilms tumors and hyperplastic nephrogenic rests are hypointense relative to normal renal tissue. [33]

Because MRI involves no radiation, this imaging study plays a unique role in the diagnosis and management of pediatric abdominal masses. For instance, whole-body MRI may compete with PET in staging abdominal tumors. Specific advantages of magnetic resonance studies include their usefulness in determining the resectability of tumors with MRI and MRA; the staging of neuroblastomas in the bone marrow, lymph nodes, liver, and spinal canal; evaluating responses of bilateral Wilms tumors and nephroblastomatosis; and detecting pelvic tumors on sagittal sections and detecting peritoneal tumors with contrast enhancement. [32]

Ohnuma et al performed MRI in 126 children with malignant solid tumors, [34] and the investigators judged whether MRI and CT studies yielded equivalent information or whether one study was superior to the other. In 47% of patients, the tumors were better visualized with MRI than with CT. In 43%, MRI was superior to CT for evaluating the local spread of tumor. MRI and CT differed little in the identification of lymph node metastases. Without requiring the injection of intravenous contrast agents, MRI accurately depicted displacement and invasion of the renal vessels by neuroblastoma. MRI was excellent in predicting kidney preservation. Finally, MRI was useful for detecting bone marrow metastases related to neuroblastoma. The coronal plane was the best imaging plane for demonstrating bone marrow involvement in the lower limbs.

Belt et al evaluated the MRI appearances and the clinical utility of MRI in 14 patients with Wilms tumors, and the MRI appearances were correlated with surgical and pathologic findings to assess their accuracy. [35] In all patients, MRI accurately depicted the primary tumor, its renal origin, the tumor margins, and local extension. The margins of the tumors were smooth and well defined in 9 of 12 cases. Local extension and size were accurately assessed. However, because capsular invasion could not be predicted, 4 surgically proven instances of capsular invasion were missed. Metastatic spread into the liver and the IVC was well documented in 4 cases and excluded in 10. MRI was sensitive for identifying lymph node enlargement in 5 of 14 patients, but it was not helpful in predicting the etiology of the enlargement. MRI signal intensity did not aid in distinguishing Wilms tumors from other solid renal tumors.


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