Centro Medico Profesional Rosancar. Barquisimeto. Venezuela.

Introduction

Most of the fetal kidney diseases are cystic and obstructive lesions [1, 2]. Fetal Kidney tumors are less frequent and the diagnosis is difficult because of the echographic features of the surrounding structures. The present case report explains echographic features of a Mesoblastic Nephroma diagnosed at the 31 weeks of pregnancy and make a brief discussion.

Case report

A 28-years-old primigravida was referred at 31st week of gestation for a targeted ultrasound examination following visualization of a severe hydramnios. Fetal biometry was consistent with gestational age. The sex of the fetus was male. A complete fetal evaluation revealed an abdominal circumference over the 95th percentile and the presence of an intraabdominal solid tumor with well defined borders that displaced the fetal liver cranially. The size of the tumor was 83 mm x 62 mm x 47 mm. (Figure 1,2).  The right kidney could not be identified and the left kidney appeared normal. Because of this findings a Congenital Mesoblastic Nephroma vs. a Wilms's tumor were proposed as possible diagnosis. There was also a severe polyhydramnios (Amniotic Fluid Index over 95th percentile).

Figures 1, 2.

Figure 3.

At 32 weeks the patient presented premature labor and spontaneous rupture of the amniotic membranes. A cesarean section was performed and a male baby was delivered. Two hours later the baby died.

Pathological findings

Postmortem examination reported a preterm male infant weighing 2320g (Figure 4). Left Kidney with the presence of fetal lobulations, corticomedular relation was conserved. Right kidney totally substituted by a solid tumor of 80 x 60 x 50 mm, with round and well defined borders,  the cut surface was yellow-grey, firm, rubbery and trabeculated, a smooth-walled cyst of 1,5 cm was present in the mid portion of the tumor.

Figure 4.

Microscopic findings

Right Kidney: The microscopic evaluation showed tight interlaced bundles of fibroblasts and myofibroblasts with eosinophilic and fibrillar cytoplasm (figure 5, 6) and round to oval nuclei. In focal areas immature cartilage (figure 7) and dysplastic glomeruli and tubules were also present (Figure 8).

Figures 5, 6.

Figures 7. 8.

Discussion

First described by Bolande and associates [3], Congenital Mesoblastic Nephroma is also known as mesenchymal hamartoma of the kidney, renal hamartoma and renal fibroma. This solid tumor is composed of immature mesenchymal cells and normal renal components, the nature and histogenesis remain controversial but it has been suggested that originates from secondary mesenchyme. The mesoblastic nephroma is the most common renal neoplasm in the first three month of life and about 120 cases in the neonatal period have been reported, and 14 cases seen in utero have been found in the literature [3-13]. All congenital mesoblastic nephroma reported were unilateral, the weight ranges from 21 to 1889 g 10,16 and diameters between 0.8 and 14 cm [10]. Congenital Mesoblastic Nephromas are encapsulated, with finger-like projections of the tumor extending in to the adjacent normal kidney. The cut surface is generally yellow-grey, firm and trabeculated and in some cases hemorrhage and necrosis can be present [14,15]. Histological features consist of bundles of spindle cells resembling fibroblasts and smooth muscle cells, incorporating scattered tubules and glomeruli, focal clusters of vascular structures, immature cartilage, sporadic calcification and islands of hematopoietic components. Increased mitotic figures may occur. On prenatal sonography, this tumor usually presents as a paravertebral abdominal non-cystic unilateral mass, with a low-level echogenicity and an inhomogeneous echo pattern. Highly echodense regions can occur. Some small echo-free areas may represent hemorrhage and necrotic tissue, as reported in cases observed postnatally [16,17]. Mesoblastic nephroma can partly show a lobation with linear demarcations indenting the surface and interlobar grooves as described in normal kidneys [18]. A well-defined border around the tumor represents the interface between the lesion and the adjacent tissue, because histologically it has no capsule. The tumor can also show an indistinct outline [7]. The space-occupying process may distort the shape of the bladder and stomach, and the dimensions of the fetal trunk may be disproportionally large [8], depending on the size of the expanding tumor. Polyhydramnios is frequent in the pregnancies complicated with this tumor, which can serve as an indicative symptom. Since amniotic fluid volume is regulated mainly by fetal swallowing and voiding [19], it is suggested that polyhydramnios resulted from excessive fetal urine production or decreased fluid absorption. Increased renal blood flow and impaired renal concentrating ability may be reasons for fetal polyuria [13]. Displacement and compression of the viscera by the tumor may cause mechanical obstruction of the intestine, interfering with amniotic fluid absorption. In relation to differential diagnosis sonography cannot provide a clear distinction between congenital mesoblastic nephroma and nephroblastoma (Wilms's tumor) because both are histological diagnoses. Although Wilm's tumor was observed in the neonatal period [20], we are unaware of a report with prenatal detection. In diffuse nephromatosis [21], both kidneys are involved and can show acoustic shadowing due to calcification. Infantile polycystic kidney disease can be recognized by no visualization of the bladder, oligohydramnios and bilaterally enlarged echogenic kidneys. Kidney enlargement in other inherited disorders such as Meckel"s syndrome is usually bilateral. Solid tumors such as neuroblastoma of adrenal gland or extra thoracic pulmonary sequestration can usually be separated from the normal-appearing kidney. Associates anomalies as polyhydramnios may lead to uterine contractions, premature rupture of membranes and preterm delivery. Suppression of uterine contractions may be obtained by tocolytic agents. In case of gross polyhydramnios, therapeutic amniocentesis may additionally be used. The visualization of a renal mass should lead to a careful sonographic search for accompanying abnormalities [22] and to serial controls to document growth of the tumor and to monitor fetal development. Although most prenatally detected fetuses with congenital mesoblastic nephroma were delivered transabdominally, the lesion per se is not an indication for primary cesarean section unless dystocia due to an extreme tumor size is present. The therapy of choice is resection of the tumor in the neonatal period [22]. Although most patients can be cured by nephrectomy alone, follow-up is mandatory, as the condition can recur.

References