Neuroblastoma Schwannian Stromapoor

Tumors in this category are composed of neuroblas-tic cells forming lobules separated by thin fibrovas-cular septa where Schwann cells (or their precursors) can (or may) be detected as slender S-100 positive cells (Shimada et al. 1985). Three subtypes, i.e., undifferentiated, poorly differentiated, and differentiating, are distinguished based on different grades of neuroblastic differentiation. It is noteworthy that in the original Shimada Classification, there were two subtypes, undifferentiated (including undifferentiat-

ed and poorly differentiated subtype of the International Classification) and differentiating (same as differentiating subtype), in this category. On gross examination, tumors are generally soft in consistency. Cut surfaces of those in the undifferentiated and poorly differentiated subtype are often hemorrhagic, while tumors in the differentiating subtype are usually tan-yellow, without hemorrhage.

Neuroblastoma, Undifferentiated Subtype (Fig. 8.1 a):

In this rare subtype, tumor tissue is composed of un-differentiated neuroblastic cells without identifiable neuropil or rosettes. In order to establish the diagnosis, supplementary tests, such as immunohistochem-istry, electron microscopy, and/or molecular/cytoge-netic analysis, are usually required.

Neuroblastoma, Poorly Differentiated Subtype (Fig.

8.1 b): Diagnosis for tumor in this subtype is relatively easy because of the presence of varying amount of neuropil and/or rosettes of the Homer-Wright type. Most of the tumor cells are undifferentiated: less than 5% of the population has morphological evidence of differentiation (see below).

Neuroblastoma, Differentiating Subtype (Fig. 8.1 c):

Tumor of this subtype usually has abundant neu-ropil. Five percent or more of the tumor cells are differentiating neuroblasts: they are characterized by synchronous differentiation of the nucleus (enlarged, eccentrically located with vesicular chromatin pattern, and a single prominent nucleolus), and of the cytoplasm (eosinophilic/amphophilic with a diameter two or more times larger than the nucleus).

Mitosis-karyorrhexis index (MKI): One of three MKI classes is assigned to the given neuroblastoma tumor. Those classes are low MKI (<2 % or <100 of 5000 mi-totic and karyorrhectic cells), intermediate MKI (2-4% or 100-200 of 5000 mitotic and karyorrhectic cells), and high MKI (>4% or >200 of 5000 mitotic and karyorrhectic cells). The MKI is defined by counting the number of tumor cells in mitosis and in the process of karyorrhexis (Fig. 8.1 d), and should reflect an average for all tumor sections available. Karyorrhectic cells show condensed and fragmented

Figure 8.1 a-f

Histology of peripheral neuroblastic tumors. a Neuroblastoma (Schwannian stroma-poor), undifferentiated subtype. b Neuroblastoma (Schwannian stroma-poor), poorly differentiated subtype. c Neuroblastoma (Schwannian stroma-poor), differentiating subtype. d Neuroblastoma (Schwannian stroma-poor) with a high mitosis-karyorrhexis index. e Ganglioneuroblastoma, intermixed (Schwannian stroma-rich). f Ganglioneuroma (Schwannian stroma-dominant), maturing subtype.

Figure 8.1 g-h g Ganglioneuroma (Schwannian stroma-dominant), mature subtype. h Ganglioneuroblastoma, nodular (composite, Schwannian stroma-rich/stroma-dominant and stroma-poor)

Figure 8.1 g-h g Ganglioneuroma (Schwannian stroma-dominant), mature subtype. h Ganglioneuroblastoma, nodular (composite, Schwannian stroma-rich/stroma-dominant and stroma-poor)

nuclear material, usually accompanied by condensed eosinophilic cytoplasm. Simple hyperchromatic nuclei without chromatin fragmentation are not included in MKI counting.

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