Mediastinal Teratoma with Nephroblastomatous Elements: Case Report, Literature Review, and Comparison with Maturing Fetal Glomerulogenic Zone/Definitive Zone Ratio and Nephrogenic Rests

Abstract

Extrarenal teratoid Wilms' tumor (TWT) is a variant of Wilms' tumor with fewer than 30 cases reported in the literature. It comprises more than 50% heterologous tissue and presents a significant diagnostic challenge due to its complex histology. We report an unusual case of mediastinal teratoma with nephroblastomatous elements in an 8-year-old female. The patient presented with respiratory distress, fever, weight loss, and a large anterior mediastinal mass. Imaging revealed a heterogeneous tumor containing fat, fluid, and calcification, suggestive of a teratoma. Surgical resection confirmed a mature cystic teratoma with foci of nephroblastoma. Pathological analysis demonstrated a mixture of ectodermal, mesodermal, and endodermal tissues alongside nephroblastomatous components. Immunohistochemistry was positive for Wilms Tumor 1 and other relevant markers, confirming the diagnosis. The patient had an uneventful postoperative course and was discharged after three days. This case adds to the growing body of research on extrarenal TWT, particularly its occurrence in the mediastinum, a rare site for such tumors. A literature review highlighted that extrarenal TWT often affects children, typically presenting in the retroperitoneum or sacrococcygeal regions, with varying recurrence rates and long-term outcomes. This case underscores the importance of histopathological and immunohistochemical analysis in diagnosing TWT and differentiating it from other mediastinal tumors to ensure appropriate treatment planning, emphasizing the need for long-term follow-up due to the potential for recurrence or metastasis. This paper also provides an in-depth look at nephron development and nephrogenic rests, highlighting the structural and functional aspects of nephrogenesis and the factors that disrupt it in fetal kidneys.

Keywords: Nephroblastoma; Teratoid Wilms’ tumor; Wilms’ tumor; immunohistochemistry; narrative review.

Figure 1

Imaging. (a) This PA view of the chest demonstrates a large mass on the right side of the chest (arrows). (b) A lateral view shows that the mass in the anterior mediastinum overlaps with the heart shadow. Axial (c) and coronal (d) contrast-enhanced CT images demonstrate an anterior mediastinal tumor (large arrows) causing mass effects in the heart and great vessels. It contains fat (small arrows), fluid, and calcification (curved arrow). The location and the presence of fat, fluid, and calcification are characteristic of a teratoma.

Figure 2

The histology and immunohistochemistry of the mediastinal tumor. This figure includes four microphotographs with included scale bars, i.e., (a) hematoxylin and eosin staining (200× magnification, scale bar 50 μm); (b) WT1 expression (100× magnification, scale bar 100 μm); (c) PAX8 expression (100× magnification, scale bar 100 μm); and (d) expression of CD56, which is a sensitive neuroendocrine marker (40× magnification, scale bar 100 μm). PAX8 is a gene that encodes a transcription factor involved in the development of the thyroid, renal, and Müllerian systems.

Figure 3

The glomerulogenic zone during ontogenesis. The glomerulogenic zone varies during ontogenesis with a decrease in thickness as the pregnancy reaches full term. The ratio of the glomerulogenic zone (GZ) to the definitive zone (DZ) is particularly critical because it mirrors the maturation of the renal parenchyma. GZ/DZ at 17 + 2 weeks of gestation (a), 20 + 1 weeks of gestation (b), 22 + 6 weeks of gestation (c), and 39 + 6 weeks of gestation (d) (hematoxylin and eosin staining). Scale bars (100 μm) are embedded in the microphotographs a, c, and d. The microphotograph b was taken at the same magnification as c. Thus, the scale bar used for the microphotograph c can be used for the microphotograph b. All microphotographs were taken during clinical autopsies performed after spontaneous stillbirths without evidence of maturation delay, and no congenital anomalies were identified during the autopsies. In all cases, consent for autopsy was granted without restrictions, and there was permission to use microphotographs for academic and educational purposes.

Figure 4

Schematic reproduction of a metanephric blastema and its evolution. A metanephric blastema steadily induces the ureteric bud to branch. The bud counteracts, tightly condensing. Sequentially, the blastema initiates renal differentiation. Potential sequelae are also displayed (see the text for details).