Congenital capillary proliferation of the kidney: A case report in a male neonate and literature review

Vascular tumors of the kidney are extremely rare in children.1Moch H. Humphrey P.A. Ulbright T.M. et al.Pathology and genetics of tumours of the urinary system and male genital organs.in: World Health Organization Classification of Tumours. 4th ed. IARC, Lyon2016: 49pGoogle Scholar, 2Cajaiba M.M. North P.E. Gong S. Dickman P.S. Mroczek-Musulman E. Sauer D.A. et al.Congenital capillary proliferation of the kidney: a distinctive renal vascular lesion of childhood.Hum Pathol. 2017; 66: 59-66Crossref PubMed Scopus (5) Google Scholar, 3Brown J.G. Folpe A.L. Rao P. Lazar A.J. Paner G.P. Gupta R. et al.Primary vascular tumors and tumor-like lesions of the kidney: a clinicopathologic analysis of 25 cases.Am J Surg Pathol. 2010; 34: 942-949Crossref PubMed Scopus (78) Google Scholar Congenital capillary proliferation of the kidney (CCPK) is a renal vascular tumor with only 4 reported cases.2Cajaiba M.M. North P.E. Gong S. Dickman P.S. Mroczek-Musulman E. Sauer D.A. et al.Congenital capillary proliferation of the kidney: a distinctive renal vascular lesion of childhood.Hum Pathol. 2017; 66: 59-66Crossref PubMed Scopus (5) Google Scholar Here, we present the rare case of CCPK with literature review. A 5-day-old male neonate presented to our hospital with a mass at the left kidney since his mother's 34th week of pregnancy. B-ultrasound examination revealed a hypoechoic renal mass, and computed tomography scan showed a renal mass at the middle and lower pole, measuring approximately 3.5 × 3.0 × 2.7 cm with hypointensity and inhomogeneous enhancement by contrast medium (Fig. 1A). The infant was clinically diagnosed with congenital mesoblastic nephroma (CMN), and radical renal resection was administered. Grossly, the radical renal specimen was 4.5 × 3.5 × 2.5 cm, and a gray-red and less-demarcated mass measuring approximately 2.2 cm in diameter (Fig. 1B) was noted. Histologically, a number of oval and spindle cells formed abundant primitive vascular cavities, entrapping small arteries and renal tubules (Fig. 1C and D). The lesion infiltrated into the peripheral renal tissues. Extramedullary hematopoiesis and mitoses were highlighted. Immunohistochemically, the spindle and oval cells were strongly positive for CD31 (Fig. 1E), CD34, and ETS related gene (ERG) and negative for D2-40, Glucose transporter protein-1 (Glut-1) (Fig. 1F), Paired box protein 8 (PAX-8), Wilms’ tumor-1(WT-1), CD10, S-100, Human melanoma black 45 (HMB45), and synaptophysin (Syn). The Ki-67 proliferation index was approximately at 10%. Fluorescence in situ hybridization revealed the negativity of ETV6 break-apart probe. The final pathological diagnosis was CCPK. No adjuvant therapy was given after surgery. The patient was uneventful 20 months postoperatively. In the literature, <300 renal vascular tumors have been reported, including the 5 CCPKs.2Cajaiba M.M. North P.E. Gong S. Dickman P.S. Mroczek-Musulman E. Sauer D.A. et al.Congenital capillary proliferation of the kidney: a distinctive renal vascular lesion of childhood.Hum Pathol. 2017; 66: 59-66Crossref PubMed Scopus (5) Google Scholar,3Brown J.G. Folpe A.L. Rao P. Lazar A.J. Paner G.P. Gupta R. et al.Primary vascular tumors and tumor-like lesions of the kidney: a clinicopathologic analysis of 25 cases.Am J Surg Pathol. 2010; 34: 942-949Crossref PubMed Scopus (78) Google Scholar CCPK was first identified in 2017 by Mariana et al.2Cajaiba M.M. North P.E. Gong S. Dickman P.S. Mroczek-Musulman E. Sauer D.A. et al.Congenital capillary proliferation of the kidney: a distinctive renal vascular lesion of childhood.Hum Pathol. 2017; 66: 59-66Crossref PubMed Scopus (5) Google Scholar It was still not adopted as an individual entity in the 4th edition of the WHO classification of pathology and genetics of tumors of the urinary system and male genital organs in 2016.2Cajaiba M.M. North P.E. Gong S. Dickman P.S. Mroczek-Musulman E. Sauer D.A. et al.Congenital capillary proliferation of the kidney: a distinctive renal vascular lesion of childhood.Hum Pathol. 2017; 66: 59-66Crossref PubMed Scopus (5) Google Scholar In our pediatric medical center, between 2010 and 2019, only 1 vascular tumor of the kidney was detected among 620 renal tumors. All the 5 CCPKs were in infants (3 males and 2 females), and 4 cases were detected prenatally or at birth. In four cases, the main complaints were renal masses. Its radiological feature was rarely reported except in our case. Our study showed it was a hypointense mass and could be inhomogeneously enhanced. The clinical and radiographical diagnosis in all the cases was CMN or multicystic renal dysplasia. Histologically, CCPK showed a number of immature vascular cavities that entrapped small arteries and renal tubules. Extramedullary hematopoiesis was a hallmark of CCPK. Immunohistochemically, vascular marker expressions, such as CD34, CD31, and ERG, and absent expression of Glut1 were helpful for the diagnosis. All the five CCPKs had similar clinicopathological features: neonates; located in the kidney; several proliferative capillaries with entrapped renal tissues; abundant extramedullary hematopoiesis; reactive lymphocyte infiltration; foci of hemorrhage; and presence of feeding and draining vessels at the periphery. All the patients received partial or total nephrectomy and were uneventful after surgery. The prognosis of CCPK was satisfactory, demonstrated by the follow-up of the total five patients. Differential diagnosis includes infantile hemangioma (IH), kaposiform hemangioendothelioma (KHE), CMN, and Wilms’ tumor (WT). IH usually appears during the first 4–6 weeks of life and exhibits classical evolution with endothelial expression of Glut1, including an early rapid growth stage, a stabilization stage, and slow spontaneous involution stage. KHE is characterized by histologically glomeruloid nodules, dilated crescentic lymphatic vessels surrounding the nodules, evident red blood cell extravasation, hemosiderin accumulation, and absent Glut1 expression on immunohistochemistry. CMN is the most common mesenchymal tumor of the kidney among infants. Fascicular spindle cells without the formation of vascular channels, negative for vascular markers on immunohistochemistry, and positive ETV6-NTRK3 gene fusion in a subset of CMN can make it different from CCPK easily. WT is the most common pediatric renal tumor and consists of triphasic components with blastemal, epithelial, and mesenchymal components. Variable expressions for WT-1, Paired box protein 2, and PAX8 can distinguish WT from CCPK. In summary, we present an exceptionally rare CCPK case. When renal mass is detected in a neonate, CCPK should be considered so that an accurate diagnosis can be easily made.