| fourth ventricle | A cavity of irregular tentlike shape extending from the obex rostralward to its communication with the sylvian aqueduct, enclosed between the cerebellum dorsally and the rhombencephalic tegmentum ventrally, having a rhomboid-shaped floor (rhomboid fossa) and a tentlike roof which in its caudal part is formed by the tela choroidea and the posterior medullary velum, in its middle part by the white matter of the cerebellum, and in its narrowing rostral part (recessus superior) by the anterior medullary velum. The fourth ventricle reaches its greatest width at the pontomedullary transition, where it expands laterally behind the cerebellar peduncles into the spoutlike lateral recess, and its greatest height at the fastigial recess, which reaches up into the cerebellar white matter. Direct communication of the brain's ventricle system and the subarachnoid space is established at the level of the fourth ventricle by a median opening in the tela choroidea, the medial aperture of Magendie's foramen, which opens into the cerebellomedullary cistern, and on both sides by the lateral aperture or foramen of Luschka, which connects the lateral recess with the interpeduncular cistern. Synonym: ventriculus quartus, ventricle of rhombencephalon. (05 Mar 2000) |
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| fourth ventricle mass | <radiology> IN ADULTS: choroid plexus papilloma, haemangioblastoma, vermian metastasis, arteriovenous malformation (AVM), inflammatory mass/cyst IN KIDS: medulloblastoma, uniform enhancement, homogeneous, ependymoma, patchy enhancement, heterogeneous, calcified (12 Dec 1998) |
| left ventricle | <anatomy> The muscular chamber of the heart which accepts blood from the left atrium and ejects it into the aorta to the systemic circulation. (27 Sep 1997) |
| Amberg's lateral sinus line | A line dividing the angle formed by the anterior edge of the mastoid process and the temporal line. (05 Mar 2000) |
| amyotrophic lateral sclerosis | A serious neurologic disease that results from the progressive degeneration of the motor neurons. (27 Sep 1997) |
| amyotropic lateral sclerosis | A chronic progressive disease of motor neurons (the nerves that come from the spinal cord to supply electrical energy to the muscles). (12 Dec 1998) |
| anterior lateral malleolar artery | <anatomy, artery> Origin, anterior tibial; distribution, ankle joint; anastomoses, peroneal, lateral tarsal. Synonym: arteria malleolaris anterior lateralis. (05 Mar 2000) |
| ventral lateral nucleus of thalamus | The composite middle third of the ventral nucleus receiving in its various parts distinctive projections from the contralateral half of the cerebellum (by way of the superior cerebellar peduncle) and the ipsilateral globus pallidus; nearly all parts of the nucleus projects to the motor cortex. Synonym: nucleus ventralis intermedius thalami, nucleus ventralis lateralis, ventral lateral nucleus of thalamus. (05 Mar 2000) |
| central and lateral intermediate substance | The central gray matter of the spinal cord surrounding the central canal. Synonym: substantia intermedia centralis et lateralis, anterior gray column, Stilling's gelatinous substance, substantia gelatinosa centralis. (05 Mar 2000) |
| central lateral nucleus of thalamus | The most lateral of the intralaminar nuclei of the thalamus. Synonym: nucleus centralis lateralis thalami. (05 Mar 2000) |
| right or left lateral decubitus film | A radiograph exposed with the subject in the decubitus position; named for the side that is dependent. Synonym: right or left lateral decubitus film. (05 Mar 2000) |
| cistern of lateral fossa of cerebrum | An elongated expansion of the subarachnoid space where the arachnoid bridges over the opening of the Sylvian fissure. Synonym: cisterna fossae lateralis cerebri. (05 Mar 2000) |
| posterior branch of lateral cerebral sulcus | The long, posteriorly-directed continuation of the lateral cerebral sulcus which extends between the temporal lobe inferiorly and the parietal lobe superiorly, its termination surrounded by the supramarginal gyrus. Synonym: ramus posterior sulci lateralis cerebri. (05 Mar 2000) |
| cross-table lateral projection | <radiology> Lateral projection radiography of a supine subject using a horizontal X-ray beam. (05 Mar 2000) |
| posterior lateral nasal arteries | Branches of the sphenopalatine artery that supply the posterior parts of the conchae and lateral nasal wall. Synonym: arteriae nasales posteriores laterales. (05 Mar 2000) |