Meninges of the Brain and Spine
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08.02.21 Outline Meninges of the Ø Anatomy of the meninges Brain and Spine Ø Enhancement Ø Techniques Ø Pathology of meninges Majda M Thurnher Medical University of Vienna | University Hospital Vienna Department of Biomedical Imaging and Image-Guided Therapy Vienna | Austria CEO of the European Board of Neuroradiology (EBNR) Past President of the European Society of Neuroradiology (ESNR) 1 2 THE MENINGES THE DURA MATTER „ the hard mother“ • Membranous coverings of the • thick, dense, fibrous and INELASTIC membrane brain and spinal • composed of two layers: cord a) the periosteal layer that lies closest to the calvarium • Three layers: dura b) the meningeal layer that lies closest to the brain mater, arachnoid tissue mater, pia mater • Mostly fused (except for the dural sinuses) • Two major functions: - Provide a supportive framework for the cerebral and cranial vasculature - Act with cerebrospinal fluid to protect the CNS from mechanical damage 3 4 THE DURA MATTER THE DURAL INFOLDINGS (processes) „ the hard mother“ • The dura mater receives its own vasculature; primarily from the FALX CEREBRI middle meningeal artery and vein TENTORIUM CEREBELLI • It is innervated by the trigeminal nerve (V1, V2 and V3) FALX CEREBELLI • Lacks the blood-brain barrier (BBB) DIAPHRAGMA SELLAE • In some areas within the skull, the meningeal layer of the dura mater folds inwards as DURAL REFLECTIONS. They partition the brain, and divide the cranial cavity into several compartments. Dural reflections refer to places where two face-to-face meningeal layers descend into the cranial cavity to form the septa that compartmentalize the brain. 5 6 1 08.02.21 FALX CEREBRI • The largest infolding • in the longitudinal cerebral fissure, which divides the two hemispheres of the cerebrum • relatively thin anteriorly where it attaches to the crista galli • broader posteriorly where it attaches to the superior surface of the tentorium cerebelli inferiorly 7 8 DIAPHRAGMA SELLAE TENTORIUM CEREBELLI • Small circular fold of dura mater that forms the roof for the pituitary gland • A small opening in its center allows passage of the stalk of the pituitary gland • The “U” shaped tentorium cerebelli runs transversely between the cerebellum and occipital lobes. • There is an opening in the falx cerebri, known as the tentorial incisura (sometimes referred to as the tentorial notch), that allows the midbrain to pass through into the middle cranial fossa. 9 10 DURAL VENOUS SINUSES THE ARACHNOID MATTER • Venous channels located intracranially between the two layers of dura „ the spidery mother“ matter • the middle layer of the meninges, lying directly underneath the dura mater • It consists of layers of connective tissue • Thin, lucent membrane • avascular • does not receive any innervation 11 12 2 08.02.21 THE SUB-ARACHNOID SPACE • Underneath the arachnoid is a space known as the sub-arachnoid space • It contains cerebrospinal fluid • Small projections of arachnoid mater into the dura (ARACHNOID GRANULATIONS) allow CSF to re-enter the circulation via the dural venous sinuses 13 14 Arachnoid granulations (Pacchionian granulation) • They most frequently occur in a parasagittal location with the sinus transversus and superior sagittal sinus being the most common locations. • incidental osteolytic, sharply circumscribed indolent-appearing • On MRI a fillinG defect in dural venous lucencies on skull CT sinuses, which can be mistaken for SVT 15 16 THE PIA MATER „ the delicate mother“ • located underneath the sub-arachnoid space • It is very thin and tightly adhered to the surface of the brain and spinal cord, it is the only covering to follow the contours of the brain (the gyri and fissures) • It is highly vascularized, with blood vessels perforating through the membrane to supply the underlying neural tissue • Two layers: a) epipial layer – connects to the arachnoid matter b) intima pia – connects to the neural tissue Leptomeninges = arachnoid + pia 17 18 3 08.02.21 THE PERIVASCULAR SPACES SPINAL MENINGES • Three layers of meninges envelop the spinal cord and the roots of spinal nerves Dura mater Arachnoid Pia mater • the pia mater forms sheaths around the blood vessels that enter and exit the brain perpendicular to the meninges, specifically from the subarachnoid space LeptomeninGes to within the brain parenchyma • This sheathing creates an interstitial fluid-filled space, known as the perivascular or Virchow-Robin space, between the vessel walls and the pia 19 20 THE SPINAL DURA MATER • Around the margin of the foramen magnum cranial dura mater is closely adherent to the bone, and is continuous with the spinal dura mater • The Spinal Dura Mater (dura mater spinalis) forms a loose sheath around the medulla spinalis • represents only the meningeal layer of the cranial dura mater (the endosteal layer ceases at the foramen magnum) • its place is taken by the periosteum lining the vertebral canal Spinal dura mater is thicker and less vascular than cranial dura mater 21 22 SPINAL SPACES EPIDURAL SPACE: between dura and periosteum • Fat • Internal vertebral venous plexus • Spinal nerve roots below S2 SUBDURAL SPACE between arachnoid and pia • Arachnoid trabeculae • CSF • Arteries • Veins 23 24 4 08.02.21 Internal vertebral venous plexus • It sits within the spinal canal within a layer of fat containing the internal vertebral venous plexus. • The vertebral venous plexus is a highly anastomotic network of valveless veins running along the entire length of the spinal canal. 25 26 Subdural hematoma Epidural hematoma 27 28 Embryology of the meninges BLOOD SUPPLY Dura: • The major arteries that supply the dura are derived from the internal carotid, • The dura mater is derived from the mesoderm, vertebral, maxillary, ascending pharyngeal, lacrimal, occipital, and ethmoidal • The arachnoid and pia mater are derived from the arteries. ectoderm • Of the arteries that supply the dura, the middle meningeal artery (MMA), which branches from the internal carotid artery’s maxillary branch, is the most important • Specifically, the development of the meninges begins with what is known as the perimedullarly mesenchyme, which contains cells from both the ectoderm and mesoderm Arachnoid: avascular • The leptomeninges forms first, as cells from the neural crest differentiate into the pia and arachnoid Pia: highly vascularized, small cappilaries 29 30 5 08.02.21 SPACES 31 32 Normal dural enhancement Outline Ø Anatomy of the meninges Ø Enhancement Ø Techniques Ø Pathology of meninges • On T1-weighted MR images: normal dura mater and inner table bone are uniformly hypointense • After contrast normal dura shows thin, linear, and discontinuos enhancement (variable thickness) 33 34 PachymeningeaL enhancement pattern Enhancement pattern Dura-arachnoid enhancement a) Pachymeningeal enhancement pattern Dura-arachnoid enhancement b) Pia-subarachnoid enhancement pattern Leptomeningeal enhancement Dural and outer layer of arachnoid pattern of enhancement! 35 36 6 08.02.21 Pia-subarachnoid enhancement pattern Enhancement pattern Leptomeningeal enhancement Pachymeningeal Pia-subarachnoid enhancement enhancement Dura-arachnoid enhancement Leptomeningeal enhancement Intracranial hypotension Meningitis (bacterial, viral, fungal) Transient postoperative changes Carcinomatous meningitis Granulomatous disease Meningioma Enhancement of sulci and subarachnoid spaces Metastatic disease Follows the pial surface of the brain and fills the subarachnoid spaces of the Lymphoma sulci and cisterns 37 38 Pachymeningeal enhancement Intracranial hypotension Dura-arachnoid enhancement Hypotension Meningioma Metastatic disease 39 40 Pia-subarachnoid enhancement Leptomeningeal enhancement Enhancement pattern Pachymeningeal Pia-subarachnoid enhancement enhancement Dura-arachnoid enhancement Leptomeningeal enhancement Thin, linear enhancement Thick, lumpy, nodular Tuberculous meningitis Meningitis (bacterial, viral, fungal) Carcinomatous meningitis 41 42 7 08.02.21 Meningitis Pia-subarachnoid enhancement Pia-subarachnoid enhancement Thin, linear Thick, nodular Tuberculous meningitis Metastatic disease Metastatic disease 43 44 Enhancement pattern Meningitis Pachymeningeal enhancement Pia-subarachnoid enhancement Thin, linear enhancement Thick, lumpy, nodular bilateral, diffuse unilateral Carcinomatous meningitis Meningitis IgG-related pachymeningitis (bacterial, viral, fungal) Sturge-Weber syndrome Neurosarcoidosis Vasculitis Vasculitis Sarcoidosis IgG- related pachymeningitis 45 46 CE-FLAIR Outline Ø Anatomy of the meninges Ø Enhancement Ø Techniques Ø Pathology of meninges CE-T1WI 47 48 8 08.02.21 CE-FLAIR CE-T1WI CE-FLAIR CE-T1WI 49 50 CE-T1WI CE-FLAIR 51 52 53 54 9 08.02.21 Outline Ø Anatomy of the meninges Infection Ø Enhancement Ø Techniques Ø Pathology of meninges 55 56 Meningitis Meningitis Imaging Findings Inflammatory infiltration of PIA, ARACHNOID, and CSF • Acute pyogenic (bacterial) • HiGh FLAIR signal of CSF spaces • Lymphocytic (viral) • Dural/meninGeal enhancement • Chronic (TB or granulomatous) • Hydrocephalus • Subdural effusions/empyema • Venous & arterial infarcts • DWI hiGh siGnal in VR Spaces 57 58 • High FLAIR signal of CSF spaces Congestion and hyperemia of the leptomeninges with exudates in the subarachnoid space (high protein content in subarachnoid spaces) 59 60 10 08.02.21 • Infarcts • Subdural effusions 61 62 • Debris level • Leptomeningeal enhancement 63 64 Inflammation • DWI: high signal in subarachnoid spaces 65 66 11 08.02.21 IgG4-related pachymeningitis Ig G4-related pachymeningitis • Rare manifestation