Lymphangiomatous hamartoma of the spleen

Absence of Nkx2-3 homeodomain transcription factor induces the formation of LYVE-1-positive endothelial cysts without lymphatic commitment in the spleen

In contrast to peripheral lymph nodes possessing lymphatic and blood vasculature, the spleen in both humans and rodents is largely devoid of functioning lymphatic capillaries. Here it is reported that in mice lacking homeodomain transcription factor Nkx2-3, the spleen contains an extensive network of lymphocyte-filled sacs lined by cells expressing LYVE-1 antigen, a marker associated with lymphatic endothelium cells (LECs). Real-time quantitative PCR analyses of Nkx2-3 mutant spleen revealed a substantial increase of LYVE-1 and podoplanin mRNA levels, without the parallel increase of mRNA for VEGFR-3 (vascular endothelial growth factor receptor Type 3) and Prox1 (Prospero homeobobox protein 1), two markers specific for LECs. Although these structures express VEGFR-2/flk-1, they lack Prox1 protein, indicating their non-LEC endothelial origin. The LYVE-1(+) structures are bordered with ER-TR7(+) fibroblastic reticular cells with small clusters of macrophages expressing MARCO and sialoadhesin. Short-term cell-tracing studies using labeled lymphocytes indicate that these LYVE-1(+) cysts are largely excluded from the systemic circulation. Cells expressing LYVE-1 glycoprotein as putative precursors for such structures are detectable in the spleen of late-stage embryos, and the formation of LYVE-1(+) structures is independent from the activity of lymphotoxin β-receptor. Thus the splenic vascular defects in Nkx2-3 deficiency include the generation of LYVE-1(+) cysts, comprised of endothelial cells without being committed along the LEC lineage.

Benign vascular neoplasms of the spleen with myoid and angioendotheliomatous features

AIMS

To present the clinical light microscopic and immunophenotypic features of a distinctive vascular neoplasm of the spleen.

METHODS AND RESULTS

Two of the splenic lesions arose in children, and one was found in an adult. They ranged from 19 to 40 mm diameter and histologically were quite similar. Sheets of large epithelioid cells with a spectrum of nuclear configurations ranging from oval and vesicular to twisted and hyperchromatic were noted in each case. Distinct or prominent nucleoli were present in many cells, and occasional cells had nuclear pseudoinclusions. In two cases, bands of basophilic, fibroblast-rich stroma with scattered chronic inflammatory cells were present. The mitotic rate ranged from 0/10 high-power fields (HPF) to 0.5/10 HPF in these epithelioid cells. The vascular nature of these tumours was manifested as a sieve-like array of round, erythrocyte-filled spaces, most with attenuated and cytologically bland lining cells. The polygonal, epithelioid cells exhibited the following phenotype: smooth muscle actin (SMA)+, muscle specific actin (MSA)+, vimentin+, CD31-, CD34-, CD21-, CD8-, CD68- (2/3 cases), S100-, while the lining cells were CD34+, vimentin+ and SMA-, with variable CD31 and factor VIII related antigen expression. Elongated SMA+, MSA+ cell processes were evident in one case, reminiscent of previously characterized myoid elements of the normal spleen. An uneventful follow-up was noted for all three patients.

CONCLUSIONS

The histology and immunophenotype set these neoplasms apart from classic hamartomas, haemangiomas and previously characterized (haem)angioendotheliomas of the spleen, and may represent proliferations of myoid elements native to the spleen.

Splenic vascular lesions: unusual features and a review of the literature

Hamartoma and peliosis are uncommon splenic lesions. Approximately 120 splenic hamartomas and 40 splenic peliosis have been reported in the English literature. In the present study, a unique case of multiple splenic hamartomas with peliosis was reported. The splenic lesions were incidental findings in a 36-year-old man with ruptured sarcomatoid renal cell carcinoma. They were diagnosed clinically as metastatic renal cell carcinoma. On pathological examination, peliosis was noted in the splenic hamartomas as well as in the splenic parenchyma. In addition, the clinicopathological features of five other splenic hamartomas (including one giant hamartoma) noted in our department were presented. A re-evaluation of the features of the splenic hamartomas documented in the English literature was also done.