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Tumors of subtentorial area make from 50% to 55% of all new growths of a brain at children. The exception makes patients till one year where tumors of supratentorial area prevail. It is also necessary to note that the highest percent of detectability of new growths in a back cranial pole is the share of age from 2 to 5 years (> 60%). In the second decade the tendency to decrease in number of subtentorial tumors and, on the contrary, to increase in the damages of a brain located over cerebellar mashed is noted. Ratio of floors approximately identical.
Basic number of tumoral processes of subtentorial localization is made by tumors of hemispheres of a cerebellum and a trunk of a brain. They are followed by tumors of the IV ventricle, covers, cranial nerves and structures of a base of skull.
Tumors of a brainstem and hemispheres of a cerebellum are provided, generally by glial new growths of various degree of a fabric differentiation. At the same time gliomas (an astrocytoma of a trunk and hemispheres of a cerebellum, an ependymoma of the IV ventricle) belong to the most often met subtentorial new growths in children's population of neurooncological patients. Further primitive neuroectodermal tumors (a medulloblastoma, an ependymoblastoma, a neuroblastoma), tumors of a vascular texture (papilloma, a carcinoma), metastatic defeats and new growths of a base of skull (a rhabdomyosarcoma, a chordoma, a chondrosarcoma) follow.
The medulloblastoma belongs to one of the most often found tumor of a back cranial pole at children (according to different statistical data from 30% to 40% of new growths of ZChYa), taking the second place on frequency among tumors of all TsNS in this age category (to 20%). The peak of occurrence falls on the first decade of life with dominance of boys (2:1 — 4:1). Medulloblastomas belong to quickly growing tumors — symptoms of defeat develop within several weeks, stretch less often about several months. Symptoms of a disease are caused, generally by growth of a tumor and a prelum of likvoroprovodyashchy ways with forming of obstructive hydrocephaly.
The medulloblastoma is an embryonal tumor of a cerebellum which histogenesis is connected with cells of an outside granular layer of a cerebellum and a back cerebellar sail. Two histologic options of a medulloblastoma — "classical" structure and desmoplastic medulloblastomas are allocated. The last till 70th carried in category of mesenchymal tumors and designated the term "cerebellum sarcoma". The majority of medulloblastomas, irrespective of their gistostruktura, burgeon through thickness of a soft meninx in SAP. Metastasises of medulloblastomas on likvorny system are noted in 60% of supervision. The disseminated small metastatic nodes in SAP of a head and spinal cord, walls of lateral ventricles are most characteristic, however forming of large solitary metastasises in the field of the hiazmapny tank and basal departments of frontal lobes is sometimes possible.
Fig. 1. Medulloblastoma of the IV ventricle (age of 15 years). MRT in a sagittal projection shows volume education in a projection of lower parts of the IV ventricle and the lower worm of a cerebellum which presses in a big occipital opening.
Fig. 2. Medulloblastoma of the IV ventricle (age of 5 years). Axial KT (a) with contrast strengthening reveals the increased density the tumor located in a projection of a worm and the IV ventricle. There is a distribution of a tumor through Lyushk's opening in the mosto-cerebellar tank. MRT (—) supplements information on prevalence of a tumor obtained at KT.
Though the medulloblastoma has no capsule, the stroma of a tumor is located compactly, having rather accurate contours and rounded shape; at the small sizes of a tumor its dorzalny arrangement in relation to a cavity of the IV ventricle well is defined. The majority of medulloblastomas represents rather dense formations of gray-pink color from mikrokaltsinata, medium-sized cysts and sites of hemorrhages.
Three quarters of medulloblastomas strike a worm of a cerebellum, at the same time medial departments of hemispheres, and a tumor are also involved, displacing the IV ventricle ventrapno and tamponing its gleam, can infiltrirovat a dorzalny surface of a trunk of a brain. The caudal pole of a tumor usually extends in the big occipital tank (fig. 1). Unlike the EDS, distribution to the lateral tank of the bridge is not typical for medulloblastomas though it can be observed (fig. 2). Lateral localization of medulloblastomas is characteristic more of children of the senior age group (fig. 3), at the same time they have less accurate contours and more often (15 — 20%) the kistoobrazovaniye is observed.
Fig. 3. Medulloblastoma (age of 10 years). MRT in the T2 mode (a) and T1 (b) after intravenous contrast strengthening defines the big sizes the tumor located in lateral departments of the left half of a back cranial pole and which is intensively accumulating a contrast agent. The brainstem and Ivzheludochek are compressed.
Fig. 4. Medulloblastoma of the IV ventricle (age of 6 years). On a series of axial KT (and, b) with contrast strengthening the tumor located in Ivzheludochka projection comes to light the increased density. Is defined mikropetrifikat in structure of a tumor. MRT in the T2 (v) mode and T1 (g) shows not homogeneous structure the new growth having raised in the T2 mode and lowered in the MR-signal mode T1. The tumor geterogenno accumulates a contrast agent (d, e).
In typical cases of a medulloblastoma are defined on KT as volume formations of a rounded or oval shape, it is heterogeneous the accumulating KV located in the projections of a worm and medial departments of hemispheres of a cerebellum which are displacing or filling the IV ventricle. Rather often (but less than at MRT) cysts are defined (to 65%), mikrokaltsinat (fig. 4) quite often come to light. Hydrocephaly is higher than the located departments of ventricular system and peritumoralny hypostasis are observed in most cases (90 — 95%). Contrast strengthening is noted more than in 90% of supervision and has mainly homogeneous expressed character though tumors can meet the minimum or total absence of contrasting. Sometimes sites of hemorrhages in fabric of a tumor or necrotic cavities (fig. 5) are found.
Fig. 5. Medulloblastoma of a back cranial pole (age 2 years). On axial KT (a) in a projection of the left half of a back cranial pole the tumor with a set of petrifitsirovanny sites comes to light the big sizes. On MRT in the T2 (b) mode and T1 (in, d) the tumor occupies the most part of the left half of a back cranial pole, extending to the supratentorial area and the vertebral channel. In a stroma of a tumor the centers of a cystous degeneration and hemorrhage are visualized.
On MRT medulloblastomas are characterized geterogenno by the changed signal usually lowered (various degree) in the T1 mode, varying from hypo - to hyper intensive on T2-the weighed tomograms (fig. 6, see fig. 4). On sagittal tomograms the arrangement of both upper, and lower poles of a tumor well is defined, the last is usually located in the big occipital tank. Full MR-research of a head and spinal cord with contrast strengthening which is recommended always at suspicion on a medulloblastoma allows to judge existence of innidiation of this tumor on subarachnoid spaces (fig. 7). Nature of accumulation of a contrast agent is very variable, its heterogeneous accumulation in fabric of a tumor (fig. 8) meets more often. In literature isolated cases of innidiation of a medulloblastoma in a skeleton bone, in particular, in vertebrae where they cause osteoplastic changes, and also in an abdominal cavity after the shunting operations for occlusion of likvoroprovodyashchy ways a tumor are also described.
Astrocytomas concern to one of extended (after medulloblastomas) tumors of a back cranial pole at children and make 30 — 40% of all subtentorial new growths of children's age. Histologically is most often pilotsitarny ("juvenile" from 75 to 85%) and fibrillar diffuzno growing astrocytomas (to 15 to 20%). Malignant forms of tumors, such as an anaplastic astrocytoma and a glioblastoma as well as an oligodendroglioma, meet seldom. On localization of an astrocytoma strike cerebellum hemispheres in 40% and a brainstem approximately in 20% of cases.
Fig. 6. Medulloblastoma of the IV ventricle (age of 7 years). In a projection of the IV ventricle of MRT shows a homogeneous structure the new growth having raised in the T2 (a) mode and lowered in the T1 mode (c) a MR-signal.
Fig. 7. Medulloblastoma of the IV ventricle (age of 13 years). Tumoral nodes (metastasises) in walls of bodies of lateral ventricles and the left frontal area are defined on brain MRT in the T2 mode (and, b) and T1 (in, e) in addition to a tumor in a projection of a worm of a cerebellum and the IV ventricle. When carrying out MRT against contrast strengthening (e, g) diffusion innidiation of a tumor on subarachnoidal covers of a head and spinal cord is revealed.
Pilotsitarny astrocytomas are one of high-quality types of ASTs. The macroscopic type and nature of growth of PASTs is defined by their localization and age. In particular, PASTs of hemispheres of a cerebellum most often form a small solid node in a wall of a large tumoral cyst. Typical cerebellar ASTs at children is the cystous tumor (60 — 80%) while at adults solid. PASTs of hemispheres of a cerebellum — a frequent new growth of ZChYa within the first decade of life (from here the second name — juvenile PASTs). At a radical oncotomy the forecast favorable and five-year survival makes 86 — 100%, and twenty-year-old — 70%.
In most cases PASTs are localized on the average line, that is proceed from a worm (to 85%).
Hemispheres of a cerebellum are surprised in 15% of supervision. The tumor, as a rule, consists of most cystous part with well delimited solid node which is located on one of its walls. The cyst is characterized by existence of a site of the lowered density at KT, a thicket by poorly hyper intensive MR-signap in relation to liquor on T1 - and a high signal on the T2-weighed MR-tomograms (fig. 9). Character of the image of a solid component, its form, the sizes are rather variable, as well as type of accumulation of a contrast agent (fig. 10, 11, 12).
Fig. 8. Medulloblastoma of the IV ventricle (age of 13 years). Tumoral education in a projection of the IV ventricle and a worm of a cerebellum is defined on brain MRT in the T1 mode to (and) and after (c) contrast strengthening. The contrast strengthening expressed has heterogeneous character.
Fig. 9. Pilotsitarny astrocytoma (age of 6 years). Volume education, the lowered density is defined on KT (a) in a cavity of the IV ventricle. MRT executed in the T2 (b) mode and T1 (in, d) visualizes a tumor which completely tampons a cavity of the IV ventricle and extends through Lyushk's opening on the right. Border between a tumor and a brainstem accurate.
At the same time contrast strengthening is observed in 95% of all supervision. Contrasting of walls of cysts variously — from total absence to the expressed extent of accumulation of a contrast agent (fig. 13, 6-14). Purely solid PASTs meet rather seldom — to 10%. In tumor fabric at KT petrifikata (10 — 20%) (fig. 15) can be defined. At localization of process in a grub of a cerebellum, medial departments of hemispheres of a cerebellum, as a rule, at the time of diagnosis gidrotsefalny expansion of the above-located departments of ventricular system (fig. 16) is observed.
Fig. 10. Pilotsitarny astrocytoma (age of 7 years). On KT (a), axial T2it the 1-weighed MRT (c), and also on axial and sagittal T1 - the weighed images after intravenous strengthening (e) the tumor of the mixed structure in a projection of the IV ventricle is visualized
Fig. 11. Pilotsitarny astrocytoma (age of 12 years). On T2 (a) and T1 (b) of the weighed MRT, and also on axial and sagittal T1 — the weighed images after intravenous strengthening (in, d) the tumor of the mixed structure in a projection of the IV ventricle and the right hemisphere of a cerebellum which is intensively accumulating a contrast agent is visualized.
Fig. 12. Pilotsitarny astrocytoma (age of 5 years). On T2 (and, b) and T1 (in, d) the weighed MR-tomograms in a projection of the left hemisphere of a cerebellum decides a tumor of the mixed structure on mainly solid component.
Fig. 13. Pilotsitarny astrocytoma of the left hemisphere and worm of a cerebellum (age of 15 years). On series of axial MRT to (and, b) and later (in) intravenous contrast strengthening the tumor decides on accurate contours of a heterogeneous structure. The cystous part has raised MP сигнапа in the T2 mode. Contrast strengthening has heterogeneous character.
Fig. 14. Pilotsitarny astrocytoma of the right hemisphere and worm of a cerebellum (age of 14 years). The tumor is defined on MRT to (and, b) and after (in, d) intravenous contrast strengthening a heterogeneous structure. The cystous part has the raised MR-signal in the T2 mode. Contrast strengthening has heterogeneous character, improving delimitation and structures of a tumor. Walls of a tumoral cyst save a contrast agent.
Fig. 15. Pilotsitarny astrocytoma of a cerebellum (age of 16 years). KT (a) defines a tumor from petrifikata and a cystous component in a projection of a worm and both hemispheres of a cerebellum. On a series of axial MRT in the T2 mode (c) and T1 (g) the zone of change of the MR-signal has more extensive character.
The group of fibrillar (diffusion) ASTs allocates astrocytomas of low degree of a zlokachestvennost (ASTs NSZ) or high-quality astrocytomas, anaplastic ASTs (ANASTS) and glioblastom (GB) though the last two types of new growths (especially GB) strike structures of ZChYa quite seldom. These tumors are characterized by the diffusion growth and in general the adverse forecast.
The high-quality astrocytoma macroscopically represents a new growth which slightly differs from brain substance on color and density, is characterized by infiltrative growth, its contours are lost among not changed structures. The consistence of a tumor varies from dense to jellylike. In it cysts can be formed, but sites of a necrosis and hemorrhage are not typical.
Fig. 15 (continuation). The cystous part of a tumor has the raised MR-signal in the T2 mode. The solid part of a tumor badly differs from marrow.
Fig. 16. Pilotsitarny astrocytoma of a worm and left hemisphere of a cerebellum (age of 8 years). On the MRT series in the T2 (a) mode and T1 (c) after intravenous contrast strengthening the tumor decides on a big cystous component of the big sizes of the mixed structure. Walls of a cyst do not save a contrast agent. Gidrotsefalny expansion III and lateral ventricles is defined.
According to KT — it, as a rule, from-gipodensnoye the education which is badly delimited from surrounding marrow. At the identical density of a tumor with marrow and absence of the expressed mass effect on KT can not come to light at all. Petrifikata in fabric of a tumor meet not often (no more than 20% of cases). Contrast strengthening is heterogeneous or in general is absent. Prevalence of defeat is better estimated by the given MRT. At MRT ASTs from - or gipointensivna on the T1-weighed tomograms also have is heterogeneous the raised signal on the T2-weighed tomograms. The pathological site has indistinct contours, peritumoralny hypostasis — minimum (fig. 17,6-18). Quite often cystous forms of tumors (fig. 19) meet. Accumulation of a contrast agent varies — from considerable in one cases, practically to total absence — in other (fig. 20, 6-21). However, in general contrast strengthening is not typical for fibrillar high-quality ASTs that is one of the differential diagnostic characters distinguishing them from PASTs. Hemorrhages in solid or cystous parts of a tumor are also observed seldom.
The anaplastic (malignant) astrocytoma is intermediate between an astrocytoma of NSZ and GB. Macroscopically AnASTs represents a tumor with cysts and sites of hemorrhages, with a marrow infiltration on the periphery. Big heterogeneity of density on KT and the MR-signal on T1-and the T2-weighed tomograms (fig. 22) in general is characteristic of AnASTs. The expressed peritumoralny hypostasis is more characteristic of this form of a tumor. Sites of the raised signal T1 - and lowered on the T2-weighed tomograms can indicate existence of hemorrhagic components. After administration of contrast medium its expressed heterogeneous accumulation in a tumor stroma is characteristic, also peripheral contrasting (fig. 23) can meet. In certain cases accumulation of a contrast agent can not be observed.
Fig. 18. Fibrillar astrocytoma of a cerebellum (age of 14 years). The tumor without peritumoralny hypostasis is defined on MRT in the T2 (a) mode and T1 (b) in medial departments of hemispheres of a cerebellum mainly cystous structure.
Fig. 17. Fibrillar astrocytoma of a worm and left hemisphere of a cerebellum (age of 16 years). On the tomogram in the sagittal and axial plane volume formation of a heterogeneous structure is defined. The cystous part of a tumor has the lowered MR-signal in the T1 (a) mode and hyper intensive in the T2 (b) mode.
Glioblastoma treats the rare tumors met within structures of ZChYa. In literature there are only separate works analyzing a small number of supervision with tumors of this histologic structure. More often the GB is localized in a hemisphere and a grub of a cerebellum, is more rare within a brain trunk. KT and MR-of its manifestation are not specific. Differential diagnosis with metastatic defeat is complicated. Nevertheless, heterogeneity of density (on KT) and the MR-signal with existence of the centers of intra tumoral hemorrhages, heterogeneous or ring-shaped contrasting after intravenous administration of a contrast agent, wider zone of an infiltration and the expressed peritumoralny hypostasis allow to assume this type of a new growth (fig. 24).