falx cerebelli
dissection of cranial cavity showing the infra - tentorial space. note three distinct folds of falx cerebelli (f1: middle falx, f2: right falx, f3: left falx, tc: tentorium cerebelli )
falx cerebelli is between 2. 8 and 4. 5 cm in length and
triple falx cerebelli associated with two aberrant venous sinuses in the infra - tentorial compartment of posterior cranial fossa .
a complex dural - venous variation in the posterior cranial fossa: a triplicate falx cerebelli and an ...
duplicated, fenestrated, small and complete absence are the reported variations of the falx cerebelli. occurrence of triple falx cerebelli associated with two aberrant venous sinuses in the floor of the posterior cranial fossa is seldom reported in the literature .
browder j, kaplan ha, krieger aj. venous lakes in the suboccipital dura mater and falx cerebelli of infants: surgical significance .
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milwaukee, wisconsin: 2006. a triple dural - venous variation in the posterior cranial fossa: a duplicated plus accessory falx cerebelli and an aberrant venous sinus .
a third, the falx cerebelli, projects downward from the tentorium cerebelli between the two cerebellar hemispheres. the outer portion of the dura mater over the brain serves as a covering, or periosteum, of the inner surfaces of the skull bones .
the falx cerebelli is a small sickle - shaped fold of dura mater situated below the tentorium cerebelli. it projects forward into the posterior cerebellar notch. occipital sinus is situated along its posterior attachment to the internal occipital crest. 1 variations in the morphology of the falx cerebelli are very rare. duplicated, triplicated, fenestrated, small and complete absence are some of the reported variations of the falx cerebelli. 2 - 7 the formations of dural venous sinuses are concurrent with the development of dural folds. hence the duplicated falx cerebelli are usually associated with duplicated occipital sinus and occurrence of such cases has already been reported. 3 the occurrence of triplicated falx cerebelli associated with an aberrant venous sinus in the floor of the posterior cranial fossa has been reported. 3 herein, we report a case of triple falx cerebelli associated with two aberrant venous sinuses in the infra - tentorial compartment of posterior cranial fossa. knowledge of incidence of such rare complex dural - venous variation is important for neurosurgeons and neuroradiologists to avoid iatrogenic injuries during suboccipital approaches and erroneous interpretation during diagnostic and operative procedures in the posterior cranial fossa. 3
the falx cerebelli is a small infolding of the dura in the sagittal plane over the floor of the posterior cranial fossa. it partially separates the two cerebellar hemispheres 1 .
tubbs rs, dockery se, salter g, elton s, blount jp, grabb pa, oakes wj. absence of the falx cerebelli in a chiari ii malformation .
shoja mm, tubbs rs, khaki aa, shokouhi g. a rare variation of the posterior cranial fossa: duplicated falx cerebelli, occipital venous sinus, and internal occipital crest .
folds of the meningeal layer of the dura mater, the falx cerebri and tentorium cerebelli, traverse the vertebrate intracranial cavity and thus compartmentalise the brain. the falx cerebelli, another dural fold, is found in the posterior cranial fossa and attaches to the inferior aspect of the tentorium cerebelli and to the internal occipital crest. we present a case of a duplicated falx cerebelli, occipital venous sinus and internal occipital crest that was detected upon routine dissection of a male cadaver. since haemorrhage of a dural venous sinus can be a fatal complication of posterior cranial fossa surgery, knowledge of venous sinus variations in this region may prevent unpredictable complications during intracranial procedures .
closer view of dissection of cranial cavity showing the infra - tentorial space. note three distinct folds of falx cerebelli (f1, f2 & f3). the right aberrant venous sinus (ras) connected the right sigmoid sinus (ss) with the ipsilateral transverse sinus. the left aberrant venous sinus (las) connected the left sigmoid sinus (ss) with the ipsilateral transverse sinus. (f1: middle falx, f2: right falx, f3: left falx, tc: tentorium cerebelli, pt: petrous part of the temporal bone )
the main (middle) falx divided into two parts near the foramen magnum and there was only one occipital venous sinus in its posterior attachment. it terminated at the confluence of sinuses bilaterally. on each side of the middle falx cerebelli, at the floor of the posterior cranial fossa two aberrant dural venous sinuses were observed. the right aberrant venous sinus connected the right sigmoid sinus to ipsilateral transverse sinus. it travelled along the posterior margin of the right falx cerebelli to enter the ipsilateral transverse sinus. the left aberrant venous sinus connected the left sigmoid sinus to ipsilateral transverse sinus. it travelled along the left side of the left falx cerebelli (
3. mavridis in, lontos k, anagnostopoulou s. absent falx cerebelli: report of a rare case. anat sci int. 2013; 88 (3): 181 - 2 .
shoja mm, tubbs rs, loukas m, shokouhi g, oakes wj. a complex dural - venous variation in the posterior cranial fossa: a triplicate falx cerebelli and an aberrant venous sinus .
4. tubbs rs, dockery se, salter g et - al. absence of the falx cerebelli in a chiari ii malformation. clin anat. 2002; 15 (3): 193 - 5 .
... the variations of the dura mater and its folds are seldom reported in the literature [ 4, 5 ]. among these are duplication of the hemispheric convexity dura [ 6 ] duplication of the spinal dural sheath [ 7 ], presence of an accessory falx cerebri [ 8 ], and duplicated, fenestrated or small falx cerebelli [ 4, 5, 9101112. hassan m and das ac, 1969 [ 13 ] found that the falx cerebelli was double in 76 of 100 cadavers... .
the incidence of variations of falx cerebelli was studied in 52 adult cadavers of south indian origin, at kasturba medical college mangalore, after removal of calvaria. in eight (15. 4 %) cases, we observed duplicated falx cerebelli along with duplicated occipital sinus and internal occipital crest. the length and the distance between each of the falces were measured. the mean length of the... [ show full abstract ]
... the falx cerebelli, which may be divided inferiorly to create a v - shaped space, the so - called vermian fossa [ 3 ]. the variations of the dura mater and its folds are seldom reported in the literature [ 4, 5 ]. among these are duplication of the hemispheric convexity dura [ 6 ] duplication of the spinal dural sheath [ 7 ], presence of an accessory falx cerebri [ 8 ], and duplicated, fenestrated or small falx cerebelli [ 4, 5, 9101112... .
the iss runs parallel to the sss in correspondence to the free margin of the cerebral falx, receiving blood from the middle regions of the brain that drains into the sss through the venous vessels of the cerebral falx .
during regular dissection classes, we came across tripled falx cerebelli in a male cadaver. the main (middle) falx cerebelli was large and was attached to the internal occipital crest. it contained the occipital sinus. there were two smaller folds (right and left), one on either side of the falx cerebelli. there were two aberrant venous sinuses; each one connecting the ipsilateral sigmoid and transverse sinuses with each other. the complex dural - venous variation reported here is seldom reported in the literature. knowledge of such variation is important for neurosurgeons and neuroradiologists as these aberrant folds could cause haemorrhage during suboccipital approaches or may lead to erroneous interpretation during imaging of the posterior cranial fossa .
the dura mater, arachnoid, pia mater, falx and tentorium cerebelli receive their sensitivity from the cranial nerves: essentially — as we shall see — from the trigeminal nerve. others, like the trochlear, make their rather unexpected contributions .
during a regular dissection class for medical undergraduates, we came across a tripled falx cerebelli associated with two aberrant venous sinuses, in the floor of posterior cranial fossa. it was noted in a 55 - year - old male cadaver of south indian origin, which was donated to manipal university, for the purpose of anatomical examination, medical education and research. while exposing the cranial cavity, the calvaria and brain were removed carefully. the tentorium cerebelli was reflected by cutting along its lateral border to expose the infra - tentorial compartment. the falx cerebelli was found to be triplicated (right, middle and left falces) (
lies inferior to the tentorium cerebelli. it superior border is attached to the lower aspect of the tentorium. the posterior border contains the
d' costa s, krishnamurthy a, nayak sr, madhyasta s, prabhu lv, jiji p, ranade av, pai mm, vadgaonkar r, ganesh kumar c, rai r. duplication of falx cerebelli, occipital sinus, and internal occipital crest .
... of the dura mater and its folds are seldom reported in the literature [ 21 ]. among these are duplication of the hemispheric convexity dura [ 20 ], duplication of the spinal dural sheath [ 11 ], absence or ossification of the falx cerebri [ 4, 24 ], presence of an accessory falx cerebri [ 8 ], incompetent sellar diaphragm [ 3 ] and duplicated, fenestrated or small falx cerebelli [ 6, 7, 13, 14, 21, 23 ]... .
osteopathy in the cranial field was first described by sutherland in the early part of the twentieth century. sutherland’s model has several key components: the fluctuation of the cerebral spinal fluid; the motility of the neural tube; the movement of the falx cerebri, tentorium cerebelli, and
... of the dura mater and its folds are seldom reported in the literature [ 21 ]. among these are duplication of the hemispheric convexity dura [ 20 ], duplication of the spinal dural sheath [ 11 ], absence or ossification of the falx cerebri [ 4, 24 ], presence of an accessory falx cerebri [ 8 ], incompetent sellar diaphragm [ 3 ] and duplicated, fenestrated or small falx cerebelli [ 6, 7, 13, 14, 21, 23 ]. these variations are often asymptomatic and only incidentally found during human dissection... .
the falx cerebelli is attached posteriorly in the midline to the internal occipital crest of the occipital bone where it contains the occipital sinus 2. its anterior edge exists freely between the partially separated cerebellar hemispheres in the posterior cerebellar notch. superiorly it is attached to the tentorium cerebelli 1. inferiorly, it extends to the posterior edge of the foramen magnum. at this point it sometimes divides into two separate parts which extend anteriorly either side of the foramen magnum 2 - 3 .
, black arrows) is introduced through the ring and middle fingers and directed into the deep connective tissues of the cerebellar falx. the index fingers monitor c2 .
please cite this paper as: satheesha nayak b, srinivasa rao sirasanagandla, deepthinath r, kumar n. triple falx cerebelli associated with two aberrant venous sinuses in the floor of posterior cranial fossa. amj 2013, 6, 8, 397 - 400. http / / dx. doi. org / 10. 4066 / amj. 2013. 1740
variations of the dural folds and the dural venous sinuses are seldom reported in the extant medical literature. such variations in the posterior cranial fossa may be problematic in various diagnostic and operative procedures of this region. we report our observation of an extremely rare variation of the falx cerebelli and posterior cranial fossa venous sinuses encountered upon dissection of a... [ show full abstract ]
the physician places her fingers so that she is contacting the midline of the occiput just inferior to the inion along the sagittal plane of the occiput. this approximates the location of the cerebellar falx (
the falx cerebri is the largest of the folds of dura mater. it attaches anteriorly to the crista galli, and runs posteriorly to fuse with the tentorium cerebelli. in its upper edge, it divides to form the superior sagittal sinus, and its lower edge is where it divides to form the inferior sagittal sinus. the upper edge is attached onto the frontal, parietal and occipital bones in an anterior to posterior direction, respectively. the lower edge of the falx cerebri passes down to separate the left and right cerebral hemispheres from one and other. it typically follows the corpus callosum, linking the two cerebral hemispheres .
as the tissue texture under the ring and middle fingers begins to change, the index fingers can control c2 to establish balanced membranous tension through the cerebellar falx and its dural connections to the upper cervical complex .
membrane that influences the mechanics of the cranial bones; and the movement of the sacrum. although there continues to be controversy regarding the physiological accuracy of sutherland’s model, it continues to be used throughout most of the world to discuss evaluation, diagnosis and treatment using this approach. sutherland described the cranium as a balanced membranous mechanism because of the relationship of the cranial bones to the intra - articular ligaments, the tentorium cerebelli, the falx cerebri, and the
sands sf, farmer p, alvarez o, et al. fat within the falx: mr demonstration of falcine bony metaplasia with marrow formation. j comput assist tomogr 1987; 11 (4): 602 - 605 .
develops first as two portions that become a single continuous structure later. it reflects downward between the hemispheres, attaching anteriorly and laterally to points on the skull and posteriorly to another partition, the tentorium cerebelli (also known simply as the tentorium). the
this technique uses a similar approach to a venous sinus spread technique but the intention is directed at the membranous structure, the cerebellar falx. studies have show that fibers from the cerebellar falx are continuous with dural ligaments extending into the upper cervical complex as low as c3. this technique is used to balance membranous strains in the cranial base that involve these connections. this may need to be performed prior to condylar decompression or base spread. this approach can also be used in older children with cervicogenic cephalgia .
). it ascends posterosuperiorly, nearly parallel to the internal occipital crest, to reach the attachment of the cerebellar falx. around the level of the external occipital protuberance, the artery bifurcates and anastomoses with the meningeal branches of the occipital and middle meningeal arteries
is located below the tentorium cerebelli on the middle of the occipital bone. this small dural infolding extends into the space between the cerebellar hemispheres, attaching to the occipital crest of the skull and the posterior portion of the tentorium. part of it encloses the occipital venous sinuses. the
is the second largest of the dural folds. it attaches to bony walls of the skull in the temporal, occipital, and parietal regions. the tentorium cerebelli is the infolding found between the cerebral hemispheres above and the cerebellar hemispheres below. it is only found in mammals and birds, being absent in fish, amphibians, and reptiles .
). the meninges protect the cns, and consist of three layers: the outermost dura mater, the middle arachnoid layer, and the inner pia mater. the dura layer is thick, tough, and composed of hypocellular fibrous tissue that adheres to the skull except where it invaginates into the cranial cavity to form septa (falx cerebri ,
the dural sinuses are situated between the leaves of the falx and the tentorium and are triangular in section. they drain blood from the cortex, the meninges, and the scalp (through the calvarian veins) and deliver it to the internal jugular veins. they are connected with the extracranial veins in the scalp by the emissary veins. this may explain dural involvement after cutaneous contusions or infections (
the tentorium cerebelli supports the occipital lobes above, and separates them from the cerebellum below. the internal concave surface is free and along with the dorsum sellae of the sphenoid bone, forms the boundary of the tentorial notch, occupied primarily by the midbrain. the outer convex border encloses the transverse sinus posteriorly and is attached to the inner aspect of the skull. more anterior, this margin encloses the superior petrosal sinus and is attached to the upper portion of the petrous temporal bone. toward the apex of the petrous temporal bone, the two borders of the tentorium cerebelli cross each other. the free border passes above and is anchored to the anterior clinoid process on either side. the attached border passes below and is then attached onto the posterior clinoid process. when the two borders have crossed each other, the triangular area of dura between them forms the roof of the cavernous sinus. the roof is continuous with the diaphragma sellae .
the lateral sinus connects the torcular herophili with the internal jugular veins on both sides and is formed by two components: the transverse sinus, which lies in the peripheral margin of the tentorium cerebelli, and the sigmoid sinus. the transverse sinuses are frequently of unequal size; the left one, which receives blood from the sss, is usually larger. atresia or agenesis of the transverse sinus is related to alternative filling of the sigmoid sinus by the vein of labbé. the sigmoid sinus starts at the end of the transverse sinus and reaches the jugular vein; agenesis and atresia of this sinus are very uncommon .
a long midline incision is used, extending approximately from the spinous process of the third vertebral body up into the occipital region, so that the pericranium and muscle attachments can be elevated on each side without disrupting their continuity. freeing up the muscle layer facilitates closure later. a wide craniotomy is performed to include the lateral sinuses and torcula but without extending to the foramen magnum. generally, using a high - speed air drill to perform a suboccipital craniotomy is preferred so that the bone flap may be replaced at the end of the procedure. a craniotome is used to turn the flap after first exposing each of the dural sinuses to avoid tears. brain relaxation and cerebellar retraction can be facilitated by mannitol, ventricular drainage, or removal of cerebrospinal from the cisterna magna. it is preferable to open the dura on either side of the midline so that the cerebellar falx and accompanying cerebellar sinus can be ligated and divided. the dural opening should extend bilaterally up to the lateral sinus (
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atlas and textbook of human anatomy / by johannes sobotta; edited with additions by j. playfair mcmurrich, v. 3 .
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1. singh i. textbook of anatomy: head and neck central nervous system. jaypee brothers medical pub. isbn: 9350253836 .
2. last' s anatomy: regional and applied, 12e (mrcs study guides). churchill livingstone. isbn: 0702033952 .
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the cranial nerves supply the sensitivity of the diploë, which is the spongy part of the cranial bones .
curiously, medical literature is very discreet on the subject of the innervation of sutures .
, who is our reference, provides just one piece of information on the topic: the innervation of the lambdoid sutures. he describes this as being due to a nerve filament from the supra - orbital nerve, a branch of the frontal nerve, which itself issues from the trigeminal nerve .
for us, the most important nerve relating to the cranial sutures is certainly the trigeminal because it sends filaments to the coronal suture: the queen of sutures and first in line for absorbing shocks .
the mucosa of the sinuses is very sensitive and reactive. it is the cranial nerves that provide its sensitivity. and here too, without prejudice, we detect the hand of the trigeminal nerve. with its three branches, it innervates the frontal, sphenoidal, ethmoidal and maxillary sinuses .
the sensitivity of the skin of the face and skull is furnished in large measure, though not exclusively, by the cranial nerves. to give an example, the skin on the skull also receives nerve fibers from the suboccipital nerve of arnold .
it is partly for this reason that we describe its manipulation in this book, even though it does not belong to the cranial nerves .
cranial nerve fibers, combined with those arising from the sympathetic ganglions, deliver arterial sensitivity. some migraine headaches are attributable to the vasodilatation of the arteries of the skull .
the brain is not sensitive in and of itself. intracranial sensitivity is due to the meninges and the vascular system .
the infant is supine or held in the parent’s arms. the physician sits at the infant’s head with her forearms supported. the physician places her hands beneath the infant’s head with a contact very low (inferior to inion) on the occiput (
, circle). the middle fingers approximate each other and lie just inferior to the ring fingers (asterisks). the index fingers contact the second cervical vertebra medial and posterior to its transverse processes .
once balanced membranous tension is established the position is maintained until there is a softening, a change in tissue texture or a correction of the strain .
the occipital sinus, which is the smallest dural venous sinus, runs along the inner surface of the occipital bone. the occipital sinus is attached to the posterior margin of the
and receives tributaries from the margins of the foramen magnum. it may anastomosis with the sigmoid sinuses and posterior internal vertebral plexus that drain into the torcular herophili. the occipital sinus is an important vascular structure during posterior fossa surgery. variations in the occipital sinus, such as double or oblique occipital sinuses or the absence of the occipital sinus, are observed in rare cases
). this becomes apparent when examining newborns, especially premature infants. the mobility and deformability of the cranium are remarkable, yet in the majority of cases it will resume a normocephalic appearance within the first 48 hours of life. the ability of the newborn cranium to make such drastic changes is evidence of its responsiveness to the subtle forces acting within the body. if a premature neonate is left in one position and not turned periodically, the infant will develop a flat spot over that area. the ability of the body to self - correct the deformity correlates with the length of time it has been present, and whether or not any external force, however subtle, has acted on the area. another example of the deformability of the living skull is the molding that is often present in newborns. this molding occurs in response to the forces acting on the cranium during birth. although the majority of these adaptations resolve, often a slight asymmetry remains. cadaveric specimens can be examined for evidence of asymmetries in the cranial fossa. these asymmetries develop in response to the position of fluid - filled vessels and the custard - like substance we call the brain. the asymmetries that occur in response to the intrauterine pressures applied to the emerging cranium may also leave an impression. the shape of any given head is the product of genetics and mechanics. the difference in shape between individuals is readily appreciable through palpation .
the mechanics in the cranium, albeit subtle, can be used to ascertain areas of compression and stress within the membranous articular mechanism. this requires a good
understanding of anatomy and a well - developed level of palpatory skill. the motions felt in the cranium are much more subtle than those palpated in the ligamentous mechanism of the spine or sacroiliac joint. whereas in the majority of individuals the sutures remain cartilaginous with adjoining connective tissue (pritchard), the articular surfaces in the cranium are generally serrated or beveled. this means that articular surfaces can only marginally glide or expand and contract in relation to each other. these movements are quite minimal, but they do allow for pliancy of the cranium .
finally, the outermost layer is the dura mater and surrounds the brain. it is comprised of two layers, though it is difficult to differentiate these with the naked eye. it is comprised of two fused layers – and internal meningeal layer and an outer endosteal layer. at points along its course, the dural venous sinuses separate it. the inner meningeal layer is limited internally by flattened cells. the external endosteal layer is also referred to as the endocranium. this endosteal layer is adherent to the skull, especially at the point of the sutures and also at the base of the skull. at the foramina of the skull and the sutures, the endosteal layer is continuous with the pericranium. where the endosteal layer is continuous with the foramina, it provides a sheath for the cranial nerves .
the meningeal layer sends four main areas of folds deeper into the cranial cavity. these are the
and is attached to the occipital bone. the anterior border is free and projects between the hemispheres of the cerebellum .
the diaphragma sellae forms a dural roof for the sella turcica. it covers the hypophysis, and has an opening for the infundibulum. the optic chiasma lies partly or completely above the diaphragma sellae .
). its origin is usually closer to the dural entrance than to the transverse foramen of the atlas. its initial course is along the upper posterior aspect of the extradural vertebral artery toward the posterolateral edge of foramen magnum, where it enters the intracranial dura (see
the posterior meningeal artery can be divided into an extracranial and an intracranial portion. the extracranial portion is tortuous, probably as a response to the motility of the neck
and extends from origin to the atlanto - occipital space. the intracranial portion shows a relatively straight configuration
). this pattern, on angiography, facilitates differentiation of the posterior meningeal artery from the branches of the posterior inferior cerebellar artery. the posterior meningeal artery, seen on 30% to 40% of angiograms, is easier to identify on lateral films .
the sss begins at the foramen cecum, before the crista galli, and runs along the curve of the inner table of the skull to reach the torcular herophili, where it converges with the straight sinus. their combined flows drain into the transverse sinus. the sss receives blood from frontal, parietal, and occipital superior regions of the cortex. the sss, and other sinuses, contains the arachnoid villi and granulations in which the absorption of cerebrospinal fluid takes place. there is a direct dependency of cerebrospinal fluid pressure on the intracranial venous pressure, which explains the frequent increase in intracranial pressure in cvst. the dura mater adjacent to the sinus contains important venous plexuses, which represent a potential alternative drainage route when a sinus is occluded; this explains the “empty - delta” sign, which is visible on computed tomographic (ct) scan in occlusion of the sss .
and receives blood from the vein of galen and from the iss. it ends in the torcular herophili or in the left transverse sinus .
are situated on the sphenoid bone, laterally to the sella turcica. their walls contain the cranial nerves iii, iv, v
, the intracavernous tract of the internal carotid artery, and the pericarotid sympathetic plexus are contained in their lumen. they drain the ophthalmic veins, the anterior and middle cranial fossa, and the sphenoparietal sinus (the medial extension of the superficial sylvian vein). blood drains posterolaterally along petrosal sinuses to the lateral sinus and the jugular vein through the inferior petrosal sinus. the two cavernous sinuses are connected by the intracavernous sinus, which lies on the clivus behind the sella turcica: this strict anatomical connection explains their frequent simultaneous involvement (
are four in number, two for each side (superior and inferior). the first one is the anterior continuation of the transverse sinus and corresponds to the oblique insertion of the tentorium on the rocca petrosa, ending in the cavernous sinuses. the second begins at the
inferior part of the intercavernous sinus to end, together with the sigmoid sinus, in the jugular vein .
on the occipital bone, and it drains blood from the dorsal regions of the cerebellum vermis .
the spinal cord and brain are the major coordinating and integrating structures for all physical and mental activities of the body and fortunately are well protected. the brain and spinal cord are covered by layers of tissue called the meninges. within certain layers of these meninges is a cushioning layer of fluid called cerebrospinal fluid. the meninges are composed of three membranes; moving from the outermost to the innermost covering, they are known as the dura mater (“tough mother” in latin), the arachnoid mater, and the pia mater .
magnum. it consists of two layers that are closely united except where, in certain spots, they separate. in some parts of the dura mater of the brain they separate to form the
). in other parts of the brain, the inner layer also separates from the outer layer to reflect inward and form partitions, described as complex folds that divide the contents of the cranial cavity into different cerebral subdivisions. these infoldings or
, which forms the roof of the sella turcica, the structure that encloses the pituitary gland. there is a tiny hole in the center of it, allowing the stalk (or infundibulum) of the pituitary to pass through. the anterior and posterior intercavernous sinuses are found in their respective edges of the diaphragma sella. these infoldings are illustrated in
when you consider the placement of these sturdy partitions being under and between the cerebral hemispheres as well as over and between the cerebellar hemispheres, it is fairly easy to understand how the dural infoldings brace the brain against rotary displacement .
there is no subdural space between the dura mater and the next layer of the meninges. when there is subdural space identified, it means that tissue damage has occurred to the deepest layer, creating a space .
because there is no normal subdural space, the next meningeal layer can be found immediately below the dura. this second layer is the arachnoid mater. this membrane bridges over the sulci or folds of the brain. in some areas it projects into the venous sinuses to form arachnoid villi. the arachnoid villi aggregate to form the arachnoid granulations. the arachnoid granulations are from where the cerebrospinal fluid diffuses into the bloodstream .
, which is filled with cerebrospinal fluid. all cerebral arteries and veins, as well as the cranial nerves, pass through this space. this is why you often hear of subarachnoid hemorrhage or bleed because damage to the brain has resulted in artery or vein tears and blood is released into this subarachnoid space .
closely adheres to the surface of the brain, covering the gyri (ridges) and going down into the sulci. the pia mater also fuses with the ependyma (a cellular membrane lining the ventricles) to form the choroid plexus of the ventricles .
). the middle arachnoid layer is very thin and avascular, and closely adheres to the dura mater by specialized fibroblasts. the inner pia mater is a vascular and delicate membrane, continuous with the brain and spinal cord, but is separated from the neural tissue by the subpial space. it is the pia mater which projects into the ventricles as villi and loose connective tissue stroma to form the choroid plexus, which in turn is responsible for the formation of csf .
between the arachnoid layer and the pia mater is the subarachnoid space, which contains csf. the arachnoid gives off projections of filaments into the subarachnoid space. this gives the space a spider - like appearance, consisting of a trabecular meshwork crossed by nerves, small arteries known as rete mirable, and bridging veins which connect the meningeal veins with the deeper intracranial venous system (
). the subarachnoid space is dilated in certain locations due to the variation in the contour of the brain and skull, forming pockets of csf called cisterns. the largest and most important of the cisterns is the cisterna magna, which surrounds the brainstem and cerebellum at the base of the skull. the cistern magna may be used to obtain csf (
. csf flows from the lateral ventricles into the third ventricle via the foramina of monroe, and then through the cerebral aqueduct into the fourth ventricle. the csf circulates through apertures in the fourth ventricle, the lateral foramina of luschka and the medial foramen of magendie, to the subarachnoid space. once the csf enters the subarachnoid space it flows both cephalad toward the cerebral hemispheres and caudally toward the spinal cord, ultimately being absorbed by the arachnoid villi in the dural sinuses located along the superior sagittal sinus and intracranial venous sinuses and returned to the venous circulation (
). leakage of csf manifesting as csf rhinorrhea or otorrhea may occur after a basilar skull fracture and indicates that the dura has been torn .
). the bars are then arranged in a rectangular configuration framing the operative field, facilitating placement of a retractor in the inferior position to depress the cerebellum. a cottonoid tray is fixed to the self - retaining retractor system and held by one of the retractor’s arms .
once the dura is opened, all bridging veins over the dorsal surface of the cerebellum, including the hemispheres and vermis, can be sacrificed to free the cerebellum from the tentorium. the weight of cottonoids and a copper retractor, along with gravitational forces that are exerted in the sitting position, allow sufficient depression of the cerebellum
to establish an unobstructed corridor to the pineal region under the tentorium. at this point, the operating microscope should be brought to the operating table. a microscope capable of varying the objective length from 275 to 400 mm is desirable because the operating distance for the surgeon changes throughout the operation, going from the dorsal surface of the cerebellum to the center of the third ventricle. the use of a freestanding armrest is also helpful in minimizing fatigue .
the arachnoid in the quadrigeminal region and around the incisura is usually thickened and opaque in the presence of tumors and must be opened by microdissection techniques to expose the surface of the tumor. the precentral cerebellar vein, which can be seen extending from the edge of the vermis to galen’s vein, should be cauterized and divided (
). galen’s great vein and the internal cerebral veins are well above the tumor and are not encountered in these initial maneuvers. laterally, the medial aspect of the temporal lobe and rosenthal’s veins can be seen as they course upward toward the confluence of veins in these regions. in general terms, the trajectory of the operation is toward the velum interpositum. this must be considered when attempting to remove segments of the tumor in the inferior portion of the third ventricle or directly over the quadrigeminal plate in relation to the anterior lobe of the cerebellum. the thickened arachnoid should be opened widely to appreciate the underlying anatomy. using sharp dissection, the arachnoidal opening must be kept close to the anterior surface of the vermis and cerebellar hemisphere to avoid injuring the deep venous system, keeping in mind that the initial trajectory is toward galen’s vein. the anterior portion of the cerebellum is retracted by the inferior self - retaining retractor to expose the posterior surface of the tumor .
because many of these tumors extend well into the third ventricle, even to the region of monro’s foramen, long instruments are required to reach the anterior margins of the tumor. with tumors of firm consistency, a cavitron with a long, curved tip can be helpful for debulking. a long focal length is desirable to accommodate the large instrument and maneuver into the operative field. the most difficult dissection involves the inferior portion of the tumor, where it is adherent to the collicular region of the dorsal midbrain. small dental mirrors and angled instruments may be required to remove this portion of the tumor. similarly, these techniques may be helpful for supratentorial tumor extensions. further exposure can be gained by incising the tentorium if necessary. tumors that are benign or encapsulated can usually be removed completely (
). with tumors that are incompletely resected, particularly vascular ones such as pineal cell tumors, meticulous hemostasis is crucial. surgicel is the preferred hemostatic agent, and it should be placed carefully so that it does not float and obstruct the aqueduct when the third ventricle fills with cerebrospinal fluid .
at the conclusion of the operation, after decompression of the tumor and the ventricular system, the dura can be closed to support the cerebellum. when a craniotomy has been performed, the bone flap is secured back in place with wires or miniplates. a greater degree of dural and bony closure seems to lower the incidence of postoperative aseptic meningitis .
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a short process of dura mater projecting forward from the internal occipital crest below the tentorium; it occupies the posterior cerebellar notch and the vallecula, and bifurcates below into two diverging limbs passing to either side of the foramen magnum .
a short process of dura mater projecting forward from the internal occipital crest below the tentorium; it occupies the posterior cerebellar notch and the vallecula, and bifurcates below into two diverging limbs passing to either side of the foramen magnum. synonym (s): falcula .
a sickle - shaped fold of dura mater in the longitudinal fissure, which separates the two cerebral hemispheres .
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srinivasa rao sirasanagandla department of anatomy, melaka manipal medical college (manipal campus), manipal university, madav nagar, manipal, karnataka state, india. 567104 email: moc. liamg @ tana. hianees
knowledge of incidence of a rare complex dural - venous variation, reported here is important for neurosurgeons and neuroradiologists to avoid iatrogenic injuries during suboccipital approaches and erroneous interpretation during diagnostic and operative procedures in the posterior cranial fossa .
). the length and width of all the three folds (right, middle and left falces) were measured. the distances between the two adjacent falces were also measured at the proximal, middle, and distal thirds. the length of the right, middle and left falces were 38mm, 44mm, and 36mm respectively. the width of the right, middle, and left falces were 3mm, 5mm, and 3mm, respectively. the distances between the right and middle falces were 3, 5, and 8mm at the proximal, middle, and distal thirds. the distances between the middle and left falces were 3, 4, and 8mm at the proximal, middle, and distal thirds .
schematic picture showing the right and left aberrant venous sinuses, in the floor of the posterior cranial fossa. the right aberrant venous sinus (ras) connected the right sigmoid sinus (rss) with the right transverse sinus (rts). the left aberrant venous sinus (las) connected the left sigmoid sinus (lss) with the left transverse sinus (lts). (os: occipital sinus )
to conclude, the complex dural - venous variation reported in the present case is seldom reported in the literature. awareness of such variation is important for neurosurgeons and neuroradiologists as these could be a potential source of haemorrhage during suboccipital approaches, or may lead to erroneous interpretation during imaging of the posterior cranial fossa .
the authors, satheesha nayak b, srinivasa rao sirasanagandla, deepthinath r, naveen kumar, declare that: this submission is compliant with the requirements of local research ethics committees .
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michaud j, mizrahi em, urich h. agenesis of the vermis with fusion of the cerebellar hemispheres, septooptic dysplasia and associated anomalies. report of a case .
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rollins n, ison c, booth t, chia j. mr venography in the pediatric patient .
okudera t, huang yp, ohta t, yokota a, nakamura y, maehara f, utsunomiya h, uemura k, fukasawa h. development of posterior fossa dural sinuses, emissary veins, and jugular bulb: morphological and radiologic study .
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this chapter will cover several normal anatomic findings and variations of normal cranial computed tomography (ct) and magnetic resonance imaging (mri), which occasionally are misdiagnosed as abnormalities, particularly by the more junior radiology resident struggling in the trenches during after - hours call. some of these normal variants have at one time or another also confused more senior radiologists, the author included, and it is hoped that this chapter contains useful tidbits for professionals at all levels of training, from the neophyte to the veteran .
these keywords were added by machine and not by the authors. this process is experimental and the keywords may be updated as the learning algorithm improves .
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the falx cerebelli is a small sickle shaped fold of dura mater , projecting forwards into the posterior cerebellar notch as well as projecting into the vallecula of the cerebellum between the two cerebellar hemispheres . the name comes from the latin word falx meaning " curved blade or scythe " and cerebellum meaning " brain " . its base is attached , above , to the under and back part of the tentorium cerebelli ; its posterior margin , to the lower division of the vertical crest on the inner surface of the occipital bone . the falx cerebelli generally lies somewhere between 2.8 and 4.5 cm in length and is approximately 1 – 2 mm thick . 
the falx cerebelli is a small sickle shaped fold of dura mater, projecting forwards into the posterior cerebellar notch as well as projecting into the vallecula of the cerebellum between the two cerebellar hemispheres. the name comes from the latin word falx meaning " curved blade or scythe " and cerebellum meaning " brain ". its base is attached, above, to the under and back part of the tentorium cerebelli; its posterior margin, to the lower division of the vertical crest on the inner surface of the occipital bone. the falx cerebelli generally lies somewhere between 2.8 and 4.5 cm in length and is approximately 1 – 2 mm thick.
the falx cerebelli is a small sickle shaped fold of dura mater, projecting forwards into the posterior cerebellar notch as well as projecting into the vallecula of the cerebellum between the two cerebellar hemispheres. the name comes from the latin word falx meaning " curved blade or scythe " and cerebellum meaning " brain ". its base is attached, above, to the under and back part of the tentorium cerebelli; its posterior margin, to the lower division of the vertical crest on the inner surface of the occipital bone. the falx cerebelli generally lies somewhere between 2.8 and 4.5 cm in length and is approximately 1 – 2 mm thick.