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II. Learning unit: Sacral congenital masses – Meningomyelocele, teratoma
Objectives and competencies
In this curriculum students may have opportunity to study development disorders of the lumbosacral region such as lumbar meningomyelocele or sacral teratom. Student may learn about etiologic factors and morphological variants of the disorder the course of diagnosis and most important aspects of treatment in multidisciplinary environment. The anatomic chapter summarizes embryonal development of teratom. Pathological implications describe its morphological variants. Sacral teratom as the most frequent congenital development disorder with other less frequent congenital development disorders are discussed. The radiology chapter introduces possible diagnostic modalities selected during pregnancy and imaging studies such as ultrasound, CT, isotope and MRI used for the diagnosis of sacral teratom and its associated development disorders. The clinical chapter summarizes epidemiology, clinical course, symptoms, diagnosis, differential diagnosis, and treatment modalities in an environment enriched with illustrations photos and tables.
II./1. Chapter: Sacral masses
Nándor Nagy
II./1.1.: Introduction
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The most characteristic occurrence in the third week of embryonic development is gastrulation (the formation of trilaminar embryonic disc), whereby the pluripotent stem cells of the embryo get separated into three germ layers (ectoderm, endoderm and mesoderm). The skin and its epithelial derivatives, as well as the nervous system and sensory organs develop from ectoderm; connective and supporting tissues, as well as the kidney and gonads are of mesodermal origin; whereas the endoderm gives rise to the epithelial derivatives of the gastrointestinal and respiratory tracts. Also, this is the time for the differentiation of gametogenic primordial germ cells.
The latter cells migrate out of the epiblastic layer in the second embryonic week, and settle in the wall of the yolk sac near to the allantois. Undifferentiated primordial germ cells intensively divide between the fourth and sixth embryonic weeks, and then they migrate through the mesenchyme of the hindgut into the mesentery, to colonize the gonadal blastems developing bilaterally on the dorsal body wall. Those primordial germ cells that follow an aberrant migratory path may cause the formation of tumors. The embryo undergoing abnormal gastrulation may die and get discharged from the uterine endometrium (abortion), or it may persist to undergo major transformation.
Of the various embryonic malformations, teratomas have a particular significance. The term originates from the ancient Greek 'teraton', meaning monster. Teratomas represent congenital tumors, which contain an irregular tangle (meshwork) of tissues derived from all three germ layers of the embryo, such as teeth, bone, hair, glands, enterocytes, muscle tissue. The term teratoma was first applied by Virchow (1869) for designation of certain tumors of the sacrococcygeal region.
By their anatomical localization, teratomas may form within the gonads or extragonadally. Given their incidence, they may develop in the sacrum (ca. 50 %), ovary (30 %), testis (3-5 %), mediastinum (7 %), craniocervical region (6 %), or the central nervous system (5 %). By their histological composition, mature (teratoma adultum) and embryonic (teratoma embryonale) forms of teratomas can be distinguished. The teratoma adultum types are composed of differentiated, quasi-organic structures, whereas the teratoma embryonale contains undifferentiated, embryonic tissues and organic primordia. In either type, three germ layers give rise to the - mostly benign -tumors.
The embryonic site of origin of the cells generating teratomas has long been disputed. It is surmised that such tumors derive from pluripotent stem cells of the embryo, capable of differentiating into any germ layer or their derivatives. Stem cells that are able to form teratomas likely derive from stem cells groups which have migrated out of the primitive streak. However, other experimental data suggest the formation of teratomas from primordial germ cells following an aberrant migratory path. Further evidence for the aberrant cell origin is the occurrence of ectopic germ cells in the brain tissue, the wall of gastrointestinal tract, glands or the mediastinum, which, under the effect of appropriate stimuli, may generate teratomas.
The chapter structure
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References
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Barksdale EM Jr, Obokhare I: Teratomas in infants and children. Curr Opin Pediatr 2009, 21: 344-349.
Lakhoo K: Neonatal teratomas. Early Hum Dev 2010, 86: 643-647.
Langman's Medical Embryology, 12th Edition, 2011 (Lippincott Williams & Wilkins) by Thomas Sadler Thomas W. Sadler PhD , T. W. Sadler , Jill Leland , Susan L. Sadler-Redmond
Larsen's Human Embryology, 4 Edition, 2008 (Churchill Livingstone) by Gary C. Schoenwolf, Steven B. Bleyl, Philip R. Brauer, Philippa H. Francis-West
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