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Neurosonography Part Three Harry H. Holdorf Midbrain Smallest portion Between Diencephalon and pons Surrounds Cerebral aqueduct Ventral aspect of midbrain- Cerebral peduncles Dorsal aspect cont. four rounded protuberances; called Corpora quadrigemina or quadrigeminal plate: Upper pair- Superior Colliculi( vis. Pathway) Lower part-Inferior Colliculi ( Auditory pathway) Pons Band of fibers between midbrain and medulla oblongata. Most of these fibers connect the two halves of the cerebellum to the brain stem by middle cerebral peduncles. Medulla Oblongata Extends from pons to the foramen magnum Continuous with the spinal cord Brain Stem Cerebellum Consist of two Cerebellar hemispheres which are connected by the cerebellar Vermis. Occupy the posterior fossa Located posterior to the pons and medulla oblongata. Attached to the brain by the superior, middle and inferior cerebellar peduncles. The cerebellum is responsible for coordination of the muscular activity and equilibrium. Cerebellum Ventericular System, Color pages 80, 82 The Hollow portion of Neural tube becomes ventericular system, which includes: Lateral ventericles Third Ventricle Aquaduct of Sylvius Fourth ventricle Lateral Ventericules Paired Largest CSF-filled cavities Located in the cerebral hemispheres Each LV consist of: Frontal horn Body Temporal horn Occipital horn Foramen of Monro- connects LV to the 3rd ventricle and divides the FH from the body. Lateral Ventericules’ Frontal horn In x-sec. is triangular+ concave lat. Wall Roof: Corpus Collasum Medial wall: Cavum Septum Pellucidum Lateral wall: Head of caudate nucleus Lateral Ventericules’ body Extended from Foramen of Monro back to the trigone In x-sec. view: Crescent with two concavities in the outer margin Roof: Corpus Collasum Medial wall:Cavum Septum Pellucidum Inferior concavity of Lat. Wall: Thalamus Sup. concavity of Lat. Wall: Body of Caudate Nucleus The notch between these stuctures is occupied by: Choroid plexus-posteriorly Thalamostriate vein anteriorly Lateral Ventericules’ Temporal horn Extend anteriorly from the trigone thru the TL as an arcuate structure It’s concavity is directed medially and inferiorly. Roof: Temporal lobe’s white matter Medial wall: Hippocampus Lateral Ventericules’ Occiptal horn Extends posteriorly from the trigone Pyramid shaped Medial wall: Occipital cortex+ white matter Proximal roof + Lat. Wall: Corpus collasum Note- Trigone is formed by the junction of the Temporal and Occipital horns. Third Ventricle Slit-like structure, located at midline Massa Intermedia is a bridge of soft tissue in the 3rd ventricle Lat. Wall: superiorly-Thalami, Inferiorly-hypothalami Floor: Hypothalamus & Optic Chiasma Anterior margin: Lamina terminalis & Ant. Commissure 2 recesses are extending from its anteroinferior aspect: Supraoptic recess & Infundibular recess Extending from its posterosuperior margin: pineal recess Connected to the LVs via foramen of Monro Connected to the fourth ventricle by: Foramen of Magendi or Median Aperature 2 Foramen of Lushchka or Lateral Aperature Ventericular System cont. Aquaduct of Sylvius: Connects the third and the fourth ventricles Only imaged if there is a massive ventricular enlargement Fourth ventricle: A thin but broad structure Roof: Cerebellar vermis Floor: Medula oblongata Schematic representation of the cerebral ventricular system. Note that lateral ventricles encompass the frontal horns (F.H.), body, posterior horns ( P.H .), and temporal horns (T.H.). The cerebrospinal fluid flows (1) from the lateral ventricles to the third ventricle (closed arrow) via the short foramen of Mono; (2) from the third ventricle through the relatively long aqueduct of Sylvius to the fourth ventricle (open arrow); and (3) from the fourth ventricle through the small foramina Luschka and Magendie to the cisterna magna located posterior to the cerebellum. sagittal midline MRI image of a normal third-trimester fetal brain. Structures that can be identified include: 4th ventricle (white arrowhead), corpus callosum (small black arrowhead), tectal plate (large black arrowhead), aqueduct of Sylvius (black arrow), and nasopharynx (white arrowhead). Ventricular system The blue parts are the ventricular system, while the green part lining the lateral parts of the ventricular system is the caudate nucleus. Cavum Septum Pellucidum Rumack p. 1637 CSF containing structure Positioned between the frontal horns and bodies of the two LVs This Midline cystic cavity consist of: Anterior portion= Cavum Septum Pellucidum Posterior portion= Cavum Septum Vergae Forms medial walls of LVs From 6th month of gestation CSV begins to close from posterior to anterior as term approaches Prominent landmark in premature and neonates CSP is present in 100% of fetuses, but over 85% of them fuse by 3–6 months of age. These structures normally do not connect with Subarachnoid of ventricular space Cavum Septum Pellucidum in fetus: Transverse view of the fetal head which shows the cavum septum pellucidum anterior to the thalamus in fetus: Cavum Septum Pellucidum in fetus Sonography of fetal “Agenesis of the corpus callosum”: In the axial plane the interhemispheric fissure (IHF) appears wider than usual without evidence of the cavum septi pellucidum. Coronal and sagital US images of the CSP in a neonate: Difference between cavum septum pellucidum (CSP), cavum vergae (CV), and cavum velum interpositi (CVI). 3=third ventricle, 4=fourth ventricle. Choroid plexus, Rumack p. 1637 Formed by the ependymal lining of ventricles and pia mater Majority found in the Lat. vents, passes thru the foramen of Monro and attaches to the roofs of 3rd and 4th ventricles It’s thin in the temporal horn and body of the Lat. Vents It attaches to the floor of the body of LVs and it’s point of attachment is called Telea Choroidea. In Trigone ; it thickens and forms Glomus. Note- At no time the CP passes into frontal or occipital horns. Choroid plexus CSF Circulation Choroid Plexus Produces most of CSF CSF flows through the Foramen of Monro to the third ventricle through the Aqueduct of Sylvius to the fourth Vent. It then exit the 4th vent. thought the lateral and median aperatures where it freely communicates with the subarachnoid cisterns and a small portion enters the spinal canal. The main site of passage of CSF into the venous blood is through the arachnoid villi or granulations that project into the dural venous sinuses. CSF Circulation CSF Circulation Cerebral Cisterns Cisterna Magna- Cerebellomedullary cistern Cisterna Pontis or Prepontine cistern Interpeduncular cistern Cistern of the lateral sulcus Cistern of the great cerebral vein or Superior cistern Cisterna Ambiens Quadrigeminal Cistern Cerebral Cisterns Germinal Matrix, Rumack p. 1637 Consist of loosely organized sheet of primitive neural cells, richly supplied with poorly supported capillary bed and thinwalled veins which give rise to the neurons and glia of the cerebral cortex and basal ganglia. GM can not be imaged in by either the US or CT. Germinal Matrix cont. Early in gestation GM forms the entire wall of the ventricular sys. Usually becomes avascular by the 36 weeks of gestation Last area to develop is located in the subependymal region of the caudothalamic notch; above the head of Caudate nucleus Germinal matrix is the site of the vast majority of the SHE (Subependymal hemorrhage)
