Lymphangiomas represent the lymphatic counterpart of hemangiomas. Microscopic examination shows cystic and cavernous spaces lined by endothelial cells and surrounded by lymphoid aggregates; the spaces usually contain pale fluid. They may occur on the skin but, more importantly, they also are encountered in the deeper regions of the neck, axilla, mediastinum, and retroperitoneum. Although histologically benign, they tend to increase in size after birth and may encroach on mediastinal structures or nerve trunks in axilla.
Teratomas may occur as benign, well-differentiated cystic lesions (mature teratomas), as lesions of indeterminate potential (immature teratomas), or as unequivocally
Fig. 7.31 Congenitalcapillaryhemangioma(A)atbirthand(B)at2yearsofageafterthelesionhadundergonespontaneousregression.(Courtesy of Dr. Eduardo Yunis, Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania.) http://ebooksmedicine.net malignant teratomas (usually admixed with another germ cell tumor component such as an endodermal sinus tumor). Sacrococcygeal teratomas are the most common teratomas of childhood, accounting for 40% or more of cases (
Fig. 7.32 ). In view of the overlap in the mechanisms underlying congenital malformations and oncogenesis, it is interesting that approximately 10% of sacrococcygeal teratomas are associated with congenital anomalies, primarily defects of the hindgut and cloacal region and other midline defects (e.g., meningocele, spina bifida) not believed to result from local effects of the tumor. Approximately 75% of these tumors are mature teratomas with a benign course, and about 12% are unmistakably malignant and lethal (Chapter 18). The remainder are designated immature teratomas, and their malignant potential correlates with the amount of immature tissue elements present. Most of the benign teratomas are encountered in younger infants (4 months of age or younger), whereas children with malignant lesions tend to be somewhat older.
The organ systems involved most commonly by malignant neoplasms in infancy and childhood are the hematopoietic system, neural tissue, and soft tissues (
Table 7.9 ). This distribution is in sharp contrast with that in adults, in whom epithelial tumors of the lung, heart, prostate, and colon are the most common forms. Malignant neoplasms of infancy and childhood differ biologically and histologically from those in adults. The main differences are as follows:
Relatively frequent demonstration of a close relationship between abnormal development (teratogenesis) and tumor induction (oncogenesis), suggesting a common stem cell defect.
Prevalence of genetic abnormalities or familial syndromes that predispose to cancer
Tendency of fetal and neonatal malignancies to regress spontaneously or to undergo “differentiation” into mature elements
Fig. 7.32 Sacrococcygealteratoma.Notethesizeofthelesioncomparedwiththatoftheinfant.
Table 7.9 Common Malignant Neoplasms of Infancy and Childhood 10–14 Years of 0–4 Years of Age 5–9 Years of Age Age • Better survival or cure of many childhood tumors, so that much attention is now paid to minimizing the adverse delayed effects of chemotherapy and radiotherapy in survivors, including the development of second malignancies