Case report: Diffuse hyperplastic perilobar nephroblastomatosis complicated by a unilateral Wilms tumour: diagnosis, treatment and follow-up

Nephroblastomatosis is an uncommon pathology, with distinct but rare radiological findings. With potential for malignant transformation into Wilms tumour and low survival rate for late diagnosed Wilms tumors, it is important to recognize nephroblastomatosis early, both clinically and radiographically to improve overall patient prognosis. The following describes a case of Wilms tumour complicating bilateral nephroblastomatosis.

Nephroblastomatosis is a premalignant condition typified by multiple residual embryonal cells known as nephrogenic rests [2]. Nephrogenic rests are clusters of embryonic metanephric cells found incidentally in 1% of infants that can exist as single or multiple, focal or diffuse lesions within the renal parenchyma. They are further classified based on their location within the kidney as perilobar or intralobar [3]. Perilobar rests are restricted to the peripheral renal cortex and are associated with fetal overgrowth disorders [4] while intralobar rests occur randomly throughout the renal parenchyma as focal lesions [5, 6]. Hyperplastic perilobar nephroblastomatosis is generally bilateral and the renal cortical surface consists partially or entirely of hyperplastic nephroblastic tissue in DHPLN [7]. The disease is also associated with an increased risk of developing Wilms tumour [5].

Sonographic features of nephroblastomatosis are typified by enlarged diffusely hypoechoic kidneys. CT imaging demonstrates low-attenuating poorly enhancing peripheral nodularity with scattered patches of adjacent normally enhancing renal parenchyma. On MRI, this corresponds to peripheral nodules with low-signal intensity on T1 and T2-weighted sequences when compared to normal renal parenchyma [8].

In contrast to the multiplicity of the subcapsular nephrogenic rests which define nephroblastomatosis and frequently serve as precursors to nephroblastomas (Wilms tumours); Wilms tumours typically manifests as solid intrarenal masses distorting the renal parenchyma and collecting system [9]. They are known to metastasize by direct extension displacing adjacent structures however they do not elevate or encase the aorta which differentiates this pathology from neuroblastomas [9]. They demonstrate heterogenous contrast enhancement on CT and MRI and are intrinsically of low signal intensity on T1-weighted imaging and high signal intensity on T2-weighted imaging [9]. Quantitative MRI techniques such as diffusion-weighted imaging (DWI) have proven valuable in differentiating intracranial tumours, but no such role has been validated for differentiation of nephroblastomatosis from Wilms tumour. However, preliminary data suggest that tissue cellularity is an important determinant of apparent diffusion coefficient which may help in terms of early prediction of Wilms tumour therapy response [10].

Treatment of nephroblastomatosis complicated by Wilms tumor incorporates multimodal therapy including surgery, chemotherapy and radiation, with more aggressive initial therapeutic protocols in the presence of poor prognostic factors. Poor prognostic factors include anaplastic tumour histology, tumour staging, unfavourable molecular and genetic markers and patient age greater than 2 years old [11]. Fortunately for this child, tumour histology was not anaplastic and there was no metastatic disease. In addition, one of the main reasons for this favorable outcome was the ability of the radiologist to identify the tumour while the child was still young. Overall, Wilms tumour 5-year survival rates have increased from 20% in the 1960s to 90% in 2005 clinical trials [11].

Gadolinium-enhanced T1 and T2-weighted MR imaging is often used to monitor regression or progression of nephrogenic tissue. Tumor regression is evident when there is a reduction in size of the nephrogenic tissue as well as decreased enhancement of the original lesion reflecting increased fibrosis and devascularization of the nephrogenic rests [12]. Increased lesion dimensions and signal intensity on T2-weighted images raises suspicion for tumor progression [12]. DHPLN has an unpredictable clinical course, with lesions varying in size over time. There is an increased risk of renal insufficiency, prolonged hypertension, and pulmonary complications if untreated. Additionally, as described in this case, there is an increased risk of development of a Wilms tumor.