Nephroblastoma is one of the most common unilateral or bilateral childhood malignancies, representing 5–10% of pediatric malignancies (1–2 malignancies per year per one million children). It derives from blastemal kidney cells and presents characteristic clinical and radiological features. The male-to-female ratio is 1.1:1.0. More than half of nephroblastomas occur before the age of 3 years, and 90% are diagnosed before the age of 10 years. Nephroblastomas arising during the neonatal period are frequently associated with chromosomal or congenital abnormalities like anridia, corporeal hemihypertrophia, or urinary malformations. Abdominal mass is usually a first clinical symptom. Radiologically, nephroblastoma is characteristically an intrarenal solid mass with hypoechogenic areas. Histologically, “standard” nephroblastomas contain various proportions of blastemal, epithelial, and mesenchymal components. “Defavorable” histology nephroblastomas (10% of cases) show sarcomatous, anaplastic, or blastematous predominance.

Smears in nephroblastoma are usually hypercellular. The diagnosis of nephroblastoma may be already suspected during smearing. They are composed of three cellular components which occur in various proportions: blastemal, epithelial, and mesenchymal. Depending on tumor components, triphasic, biphasic, or monophasic patterns may be observed [18–21] (Figs. 4.10, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19, 4.20, 4.21 and Table 4.3).

The major cellular pattern seen in nephroblastoma usually includes a predominance of blastemal cells [18]. Blastemal cells consist of small and round monomorphous cells with scant cytoplasm and delicate nucleoli. Anaplasia, if present, is easily identified and may present as a large, mono- or multinucleated cells with polymorphous, atypical nuclei [22]. The epithelial component consists of small-to-medium-sized round tumor cells with distinct cytoplasm, sometimes arranged in tubular structures. Finally, the mesenchymal component consists of spindle-shaped tumor cells most often arranged in loose sheets intermixed with a myxoid or collagenous matrix.

Immunohistochemistry shows positivity for vimentin, WT1, CD56, and INI1; WT1, however, is positive only in 70% of nephroblastomas. CD57 is negative. Cytokeratins are positive in the epithelial component and is therefore useful many times.

Until now, no specific chromosomal translocation has been described in nephroblastoma, and there is no specific molecular marker useful for diagnosis.

Nephroblastoma should always be differentiated from other primitive kidney tumors—e.g., clear cell carcinoma/sarcoma, congenital mesoblastic nephroma (Bolande tumor), renal cell carcinoma—and from clear cell variant and rhabdoid tumors of the kidney. Moreover, in more advanced cases, nephroblastoma should be differentiated from neuroblastoma-infiltrating renal or suprarenal tissues (Figs. 4.22, 4.23, and 4.24).

However, the differential diagnosis is also related to a particular subtype of nephroblastoma. Nephroblastoma with predominant blastemal component should be differentiated from stroma-poor neuroblastoma, clear cell sarcoma, and rhabdoid tumor. Nephroblastoma with predominant blastemal component usually exhibits minute foci of epithelial differentiation, allowing a correct diagnosis. Inversely to neuroblastoma, neuropil is always absent in nephroblastoma [9]; keeping in mind that poorly differentiated neuroblastoma does not have neuropil either, and rosettes are often absent. Nephroblastoma with predominant blastemal component is vimentin, INI1, WT1, and CD56 positive, whereas stroma-poor neuroblastoma is WT1 negative and Phox2b, tyrosine hydroxylase, CD56, NSE, NB84 and synaptophysin positive.

Clear cell sarcoma is usually triphasic, showing three cell types: large polygonal cells with abundant eccentrically placed wispy cytoplasm, usually with nuclear grooves called cord cells; spindle shaped septal cells, usually embedded in the stromal fragments; and small degenerative pyknotic cells (Fig. 4.22). However, stromal fragments with branching vascular cores and myxoid substance surrounding the vessel may be also seen. The presence of eccentric cytoplasm in cord cells and nuclear grooves are the key to differentiation from nephroblastoma, including anaplastic variants [23–25]. Clear cell sarcoma is vimentin, INI1, and CD56 positive. WT1 is negative. However, t(10;17), del(14)(q24.1q31.1) may also occur and be of precious help in the differential diagnosis.

There is no difficulty in differentiating nephroblastoma from renal clear cell carcinoma [26]. Subtypes of renal cell carcinomas exhibit a Xp11.2 translocation.

Rhabdoid tumors are composed of rhabdomyosarcoma-like cells with occasionally peri-nuclear densities which are cytokeratins and vimentin positive (dot-like) [27]. INI1 and WT are negative. A deletion of chromosome 22, however, is usually seen in rhabdoid tumor.

Epithelial-rich nephroblastoma should be differentiated from metanephric adenoma, which exhibits many overlapping morphologic patterns (Fig. 4.23). Smears in metanephric adenoma are hypercellular and composed of small oval-to-round cells arranged in a three-dimensional clusters showing microfollicular pattern and papillary configurations. Nuclear molding, irregular nuclear membrane, and distinct nucleoli with mitotic figures are usually seen. Psamomma bodies, nuclear atypia, cellular pleomorphism, and necrosis are absent [28, 29]. Metanephric adenoma is CD57 positive, while nephroblastoma is CD57 negative. Moreover, BRAF mutation is strongly in favor of metanephric adenoma.

Finally, mesenchymal nephroblastoma should be differentiated from congenital mesoblastic nephroma (also from sarcomas) (Fig. 4.24). Only simple case reports of congenital mesoblastic nephroma are known. Congenital mesoblastic nephroma of “classical type” contain spindle cells without mitoses or necrosis, reminiscent of infantile fibromatosis. No epithelial, tubular, or glomeruloid differentiation was noted [30–33]. “Cellular type” of congenital mesoblastic nephroma contains spindle- and tadpole-shaped cells with round-to-oval nuclei having small nucleoli and a smooth contour. The cytoplasm of these cells is dense and homogeneously stained. The background is composed of mucoid fibrillar material, round cells with mitoses, and necrosis [34]. The presence of t(12;15)(p13;q25), also observed in infantile fibrosarcoma, strongly argues in favor of congenital mesoblastic nephroma.

Surprisingly, only few series describe cytomorphology in nephroblastoma, but all tumors were accurately diagnosed [18–20].

As already mentioned above, immunocytochemical use of antibody against WT1 is not positive in all nephroblastomas. Furthermore, staining of nuclei may also be seen in desmoplastic small cell tumors, lymphoblastic lymphoma, and neuroblastoma, and cytoplasmic staining can be present in rhabdomyosarcoma.

Beware of poor cellular smears with necrotic material.

Recognition of nephroblastoma may be more difficult in monomorphic variants, with the biphasic variant being the most commonly diagnosed.

Approximately 300 cases of adult nephroblastoma were also described [35].

Retinoblastoma is a high-grade pediatric malignancy originating in the retina. Almost 40% of patients have a hereditary genetic defect associated with retinoblastoma. In these children, tumors are usually bilateral or unilateral but multifocal, and a mutation in the RB1 gene on chromosome 13 is present. Hereditary retinoblastomas occur quite exclusively in newborns. Non-hereditary retinoblastoma represents the remaining 60% of patients. Tumors are unilateral and occur mainly in patients around 2 years old, but 15% of them occur in newborns. Moreover, somatic amplification of the MYCN oncogene is responsible for about 2% of cases of non-hereditary, aggressive, unilateral retinoblastoma.

Leucokoria or striabism are usually the first symptoms.

Clinical and imaging modalities (ultrasonography, CT scan, and MRI) data are characteristic and frequently intraocular tumors do not require any pathological diagnostic specimen. However, in less characteristic cases, a transcleral fine needle aspiration may be practiced under general anesthesia. On the other hand, recurrences and distant metastases are valuable targets of cytopathological diagnosis [36].

Smears are usually hypercellular. Numerous small, round tumor cells are seen singly or in loose or tightly packed clusters [37]. The nuclear features include uniformly distributed nuclear chromatin, paucity of nucleoli, and nuclear molding. Two types of cells are classically recognized [38, 39]: type I undifferentiated blue cells, associated with abundant necrotic debris and portions of capillaries surrounded by perivascular tumor cells; and type II cells, which show more differentiation with cytoplasmic processes that are probably indicative of early photoreceptor differentiation. More commonly, smears contain round, polymorphous, and necrotic cell population. Some cells show V-like nuclei. Flexner-Wintersteiner rosettes, characteristic of retinoblastoma, are frequently found (tumor cells surrounding a central lumen). Ponctual or extensive necrosis associated with microcalcifications are usually seen in the background. Many mitotic figures are also present (Figs. 4.25 , 4.26, 4.27, 4.28 and Table 4.4).

Immunohistochemical staining with synaptophysin shows positivity in the cytoplasm of tumor cells [37].

Intraocular retinoblastoma should easily be differentiated from other tumors that can occur at this location, such as melanoma, lymphoma, and leukemia. However, in cases in which a metastatic site of retinoblastoma is sampled, it should be differentiated from neuroblastoma, Ewing sarcoma, and alveolar rhabdomyosarcoma. Neuroblastomas are composed of roundish neuroblasts and usually show neuropil. Neuropil is present as variable-sized extracellular pinkish and delicate debris, or is localized in the centers of Homer-Wright rosettes, whereas Flexner-Wintersteiner rosettes in retinoblastoma are composed of tumor cells surrounding a central lumen that contains cytoplasmic extensions from the tumor cells. Ewing sarcoma, similarly to retinoblastoma, may show a double population of roundish cells that are larger-clearer and smaller-darker. Moreover, in some cases rosettes are also observed. A specific clinical setting, immunostaining, and molecular markers are in favor of Ewing sarcoma. Finally, some rhabdomyosarcomas, especially of alveolar subtype localized in the orbit, may simulate retinoblastoma. These tumors exhibit a specific immunostaining and molecular markers. The presence of rosettes and type II cells with cytoplasmic processes are the two features that are most helpful in the diagnosis of retinoblastoma [38].

A high specificity of intraocular FNA procedure has been previously reported by Augsberger et al. [36], Akhtar et al. [38], and O’Hara et al. [40]. In these pioneer series a variety of intraocular neoplasms, in addition to retinoblastoma, were included, and the technique was demonstrated to be a reliable and accurate diagnostic modality in the assessment of selected pediatric ophthalmic diseases. Shields et al. [41] have analyzed 140 intraocular aspirates in retinoblastoma, and the sensitivity rate was 100% and the specificity rate was 98%. Later, the technique was adapted for diagnostic purposes in many centers and numerous cases were reported of primary retinoblastoma that were accurately diagnosed using transcleral FNA [39, 40, 42–44] or local recurrences [45]. FNA technique was also demonstrated in the diagnosis of distant metastases [46, 47].