Angularis oculi vein blood flow modulates the magnitude but not the control of selective brain cooling in sheep.

To investigate the role of the angularis oculi vein (AOV) in selective brain cooling (SBC), we measured brain and carotid blood temperatures in six adult female Dorper sheep. Halfway through the study, a section of the AOV, just caudal to its junction with the dorsal nasal vein, was extirpated on both sides. Before and after AOV surgery, the sheep were housed outdoors at 21-22°C and were exposed in a climatic chamber to daytime heat (40°C) and water deprivation for 5 days. In sheep outdoors, SBC was significantly lower after the AOV had been cut, with its 24-h mean reduced from 0.25 to 0.01°C (t(5) = 3.06, P = 0.03). Carotid blood temperature also was lower (by 0.28°C) at all times of day (t(5) = 3.68, P = 0.01), but the pattern of brain temperature was unchanged. The mean threshold temperature for SBC was not different before (38.85 ± 0.28°C) and after (38.85 ± 0.39°C) AOV surgery (t(5) =0.00, P = 1.00), but above the threshold, SBC magnitude was about twofold less after surgery. SBC after AOV surgery also was less during heat exposure and water deprivation. However, SBC increased progressively by the same magnitude (0.4°C) over the period of water deprivation, and return of drinking water led to rapid cessation of SBC in sheep before and after AOV surgery. We conclude that the AOV is not the only conduit for venous drainage contributing to SBC in sheep and that, contrary to widely held opinion, control of SBC does not involve changes in the vasomotor state of the AOV.

Dural Venous System in the Cavernous Sinus: A Literature Review and Embryological, Functional, and Endovascular Clinical Considerations.

The cavernous sinus (CS) is one of the cranial dural venous sinuses. It differs from other dural sinuses due to its many afferent and efferent venous connections with adjacent structures. It is important to know well about its complex venous anatomy to conduct safe and effective endovascular interventions for the CS. Thus, we reviewed previous literatures concerning the morphological and functional venous anatomy and the embryology of the CS. The CS is a complex of venous channels from embryologically different origins. These venous channels have more or less retained their distinct original roles of venous drainage, even after alterations through the embryological developmental process, and can be categorized into three longitudinal venous axes based on their topological and functional features. Venous channels medial to the internal carotid artery "medial venous axis" carry venous drainage from the skull base, chondrocranium and the hypophysis, with no direct participation in cerebral drainage. Venous channels lateral to the cranial nerves "lateral venous axis" are exclusively for cerebral venous drainage. Venous channels between the internal carotid artery and cranial nerves "intermediate venous axis" contribute to all the venous drainage from adjacent structures, directly from the orbit and membranous skull, indirectly through medial and lateral venous axes from the chondrocranium, the hypophysis, and the brain. This concept of longitudinal venous axes in the CS may be useful during endovascular interventions for the CS considering our better understandings of its functions in venous drainage.

New facts and the concept of physiological regulation of the dopaminergic system function and its disorders.

We present the main results of the study and justification of our opinion on the role of dopamine (DA) retrograde transfer in the cavernous sinus in the regulation of the dopaminergic (DArgic) system activity. We are convinced that under physiological conditions DA - which is continuously retrograde transferred in the cavernous sinus from venous brain effluent to arterial blood supplying the brain and carried by the arterial blood to endothelial cells and perivascular astrocytes of striatal DArgic cell groups - can inhibit dopamine transporter (DAT) expression by a down-regulation mechanism. A new concept of the genesis of DArgic system dysfunction with involvement of DA retrograde transfer in the cavernous sinus is presented. We suggest that future research that aims to explain the genesis of hypo- or hyperfunction of the DArgic system, and DArgic system dysfunction causing Parkinson's disease, attention deficit hyperactivity disorder (ADHD), schizophrenia, and many other psychiatric disorders, must involve two areas: 1) the cavernous sinus, where DA is taken up, and transferred from the venous blood of the cavernous sinus to the arterial blood supplying the brain. To regulate this process pharmacologically, understanding the mechanism and explanation of what determines its course is necessary; 2) brain DArgic structures, whose activity is regulated primarily by the action of DAT. It is essential to clarify whether the expression of the DAT is regulated directly by DA reaching the presynaptic membrane or by any factor secreted by specific perivascular glial cells (astrocytes) under the influence of DA and DA metabolites.

The internal carotid artery has a sleeve of increased innervation density within the cavernous sinus in monkeys.

The numerical density of nerve terminals of the internal carotid artery was measured using interrupted serial sections and compared with densities sampled from the major cerebral arteries of cynomolgus and rhesus monkeys. In its course through the carotid canal and the foramen lacerum the artery received few terminals. Nerve terminal density increased substantially within the cavernous sinus in 13 of 19 animals, reaching a peak shortly before emerging to join the circle of Willis. The density dropped rapidly on leaving the sinus. The increase was present in both species and rose to a mean nerve terminal density at least ten times that of any other artery measured. In 6 monkeys terminal incidence was unchanged through the sinus. The possible relevance of the nerve terminal sleeve to cerebral vasodynamics and to vascular head pain is discussed.

Gas in the cavernous sinus.

PURPOSE: To evaluate the significance of cavernous sinus gas identified on head CT scans. METHODS: Head CT scans were viewed prospectively for a period of 3 years. The charts of patients who demonstrated cavernous sinus gas were reviewed. RESULTS: Seventeen patients without head trauma and 10 patients with head trauma demonstrated gas in the cavernous sinus. None of the patients had symptoms or developed symptoms originating in the cavernous sinus. All of the patients without trauma had an intravenous line in place. Sphenoid fractures or basilar skull fractures were not a constant finding in trauma patients with cavernous sinus gas. CONCLUSIONS: In patients without symptoms referable to the cavernous sinus, gas in the cavernous sinus does not appear to be a significant finding. The gas is most likely the result of venous air emboli from intravenous lines or penetrating trauma.

Ocular pneumoplethysmography in carotid-cavernous sinus fistulas.

Pulsatile exophthalmos in association with carotid-cavernous sinus fistulas has been well defined anatomically, by angiography. This paper presents the physiological assessment of this entity, as measured with ocular pneumoplethysmography (OPG-Gee). The abnormal arteriovenous communication lowers resistance to arterial flow. This is characterized by a lowered ophthalmic systolic pressure and an increased ocular blood flow. The OPG readily documents the physiological result of therapeutic intervention.

Unusual computerized tomography appearance of a carotid-cavernous fistula. Case report.

A case of carotid-cavernous fistula characterized by an unusual computerized tomography (CT) pattern is reported. The CT study showed a hyperdense lesion in the right frontoparietal region, and angiography demonstrated an uncommonly large venous network in the same area. After embolization by a detachable balloon technique, these findings gradually resolved. The CT pattern was probably due to the unusually large venous drainage and to the related ischemia of the brain parenchyma.

Luteinizing hormone and prolactin are not retrograde transferred in perihypophyseal vascular complex in ewes.

The objective of the study was to determine whether luteinizing hormone (LH) and prolactin (PRL) can access the brain by way of transfer from the venous blood of the cavernous sinus to the arterial blood supplying the brain and hypophysis. Studies were performed on heads of 22 mature sheep isolated during different phases of the estrous cycle and perfused with autologous blood. We were not able to demonstrate any transfer of LH and PRL in the investigated periods. This suggests that molecular weight of hormone may be a main factor determining the permeation and transfer of hormones in the perihypophyseal vascular complex.

Control and autoregulation of the blood circulation in the vertebrobasilar system.

The author establishes an analogy between the control mechanism and autoregulation of the cerebral blood flow and the protection of the vascular wall of the internal carotid artery constituted by the conjunction of the 'internal carotid-cavernous sinus' system with the 'vertebrobasilar-transverse-occipital dural sinus or basilar' 'sinus' system (an extension of the cavernous sinus) in the autoregulation and control of the encephalic circulation carried out through this latter vessel, together with the protection of its vascular walls. The author believes it to be very difficult to demonstrate in practice the functioning of these mechanisms, but he argues that the unusual anatomical features of the systems are indicative of their particular physiological roles.

Physiological importance of the conjugation of the internal carotid artery and cavernous sinus.

The author considers of utmost importance the anatomical arterial-venous conjugation represented by the internal carotid artery and the cavernous sinus, as well as the carotid venous plexus which covers the internal carotid artery within the petrous portion of the temporal bone. He believes that besides protecting the vascular arterial wall in acute episodes of hypertension, it can also contribute to the mechanism of carotid blood flow. This hypothesis is based on consideration of the physiological conditions of the cavernous sinus in relation to those of other dural venous sinuses, and of the endocranial venous system and its cavernous constitution, which differs from other venous blood canals, which have their own venous physiology and different functions. He attempts to compare it with the rest of the body areas where cavernous plexuses are located and where venous pressure reaches high values, and with other regions without this morphologic constitution. He establishes a correlation resulting from a cerebrovascular resistance mechanism, the participation of which he considers to differ from those of other dural sinuses and encephalic veins. He also emphasizes physiologically the carotid siphon and believes that its participation in the hemodynamics of a hypotensive patient who is lying down, facilitates blood access to the brain, thus avoiding anoxia and brain damage, within certain limits, and constitutes an additional means of body defense.

Selective brain cooling in mammals and birds.

Artiodactyls and felids have a carotid rete that can cool the blood destined for the brain and consequently the brain itself if the cavernous sinus receives cool blood returning from the nose. This condition is usually fulfilled in resting and moderately hyperthermic animals. During severe exercise hyperthermia, however, the venous return from the nose bypasses the cavernous sinus so that brain cooling is suppressed. This is irreconcilable with the assumption that the purpose of selective brain cooling (SBC) is to protect the brain from thermal damage. Alternatively, SBC is seen as a mechanism engaging the thermoregulatory system in a water-saving economy mode in which evaporative heat loss is inhibited by the effects of SBC on brain temperature sensors. In nonhuman mammals that do not have a carotid rete, no evidence exists of whole-brain cooling. However, the surface of the cavernous sinus is in close contact with the base of the brain and is the likely source of unregulated regional cooling of the rostral brain stem in some species. In humans, the cortical regions next to the inner surface of the cranium are very likely to receive some regional cooling via the scalp-sinus pathway, and the rostral base of the brain can be cooled by conduction to the nearby respiratory tract; mechanisms capable of cooling the brain as a whole have not been found. Studies using conventional laboratory techniques suggest that SBC exists in birds and is determined by the physical conditions of heat transfer from the head to the environment instead of physiological control mechanisms. Thus except for species possessing a carotid rete, neither a coherent pattern of SBC nor a unifying concept of its biological significance in mammals and birds has evolved.

The inhibitory effect of hCG on counter current transfer of GnRH and the presence of LH/hCG receptors in the perihypophyseal cavernous sinus--carotid rete vascular complex of ewes.

The existence of the hormone passage from venous blood into arterial blood in the area of the perihypophyseal vascular complex has been demonstrated in some mammals, but its mechanism has not been defined. To study the regulatory mechanism we infused hCG into perihypophyseal cavernous sinus of ovariectomized, conscious ewes to test if the hCG would affect putative LH/hCG receptors and inhibit counter-current transfer of GnRH from the venous cavernous sinus to the arterial carotid rete. The latter study was done on an isolated head model. Ewes were ovariectomized in mid-anestrus and, after 4 to 5 wk were used in the experiments. On the day of experiment ewes were treated intramuscularly with estradiol benzoate or oil vehicle, and 18 to 20 h later were infused either with a multielectrolyte solution or hCG for 2 h via the venae angularis oculi. Immediately thereafter the ewes were anesthetized and exanguinated, and subsequently decapitated. The isolated head was perfused with Dextran in multielectrolyte. The 125I-GnRH was infused into the cavernous sinus via the venae angularis oculi for 5 min; contemporaneous samples were taken from the carotid rete and both jugular veins at 1-min intervals. Transfer of 125I-GnRH from the cavernous sinus to the carotid rete was inhibited by hCG in ewes pretreated with estradiol benzoate but not with oil (P<0.005). We collected tissue samples from the vascular complex of the cavernous sinus and carotid rete of cyclic ewes to determine the presence of LH/hCG receptors. In situ hybridization showed the presence of LH/hCG receptor mRNA transcripts in the walls of both arterial and venous compartments of the cavernous sinus-carotid rete complex, and immunohistochemistry revealed the presence of receptor proteins. These novel findings confirm previously obtained data suggesting that LH is a modulatory factor for the counter-current transfer of neuropeptides from the venous blood of the cavernous sinus to the arterial blood supplying the brain and hypophysis. The LH could modulate 125I-GnRH transfer acting directly on the vascular smooth muscle.

Branches of the intracavernous internal carotid artery and the blood supply of the intracavernous cranial nerves.

With the increasing frequency of surgical operations to the cavernous sinus greater knowledge of the microanatomy of the cavernous sinus has become necessary. The most frequently seen complications during cavernous sinus surgery involve impairment of cranial nerves. This can occur due to direct damage or ischemia. For these reasons, it is important to know the arterial supplies to the cranial nerves in the cavernous sinus and the anatomy of these branches as well. 15 formaline fixed adult cadavers were used in this study. Before the dissections, the internal carotid artery and vertebral artery were filled with coloured latex on both sides. In this report, the intracavernous branches of internal carotid artery (I.I.C.A.) were identified based on the principles of Nomina Anatomica (1989) and compared with others. In our study we found that the segment of the abducens nerve which lies in Dorello's channel was supplied by the meningeal branch; from the point at which it pierces the cerebellar tentorium, the trochlear nerve is supplied by the tentorial cerebellar artery; the posterior cerebellar artery supplies the proximal segment of the oculomotor nerve that proceeds to the oculomotor triangle. Except for these, all the cranial nerves that were located on the lateral wall of the sinus cavernosus are supplied by the tentorial marginal branch and the branches of the lateral trunk.

How can the hooded seal dive to a depth of 1000 m without rupturing its tympanic membrane? A morphological and functional study.

Recent studies using a satellite-linked dive recorder have shown that the hooded seal (Cystophora cristata), a common Arctic pinniped, can dive to a depth of > 1000 m and stay submerged for close to 1 h. At these depths the water pressure reaches 100 atm, entailing obvious risk of serious damage to the hearing apparatus, mainly the tympanic membrane (TM) and middle ear (ME). We dissected and photodocumented the temporal bones of five newborn and three adult hooded seals in order to study the temporal bone structure and reveal its protective mechanisms for extreme pressure changes. Specimens were sectioned and stained for light microscopy. The thicknesses of the pars tensa and pars flaccida were found to average 60 and 180 microm, respectively. The ME cavity hosts a cavernous tissue of thin-walled vessels beneath the modified respiratory epithelium. The ME and external ear canal (EAC) volumes can be altered appreciably by filling/emptying the cavernous tissue with blood. The ossicles were fixed by contracting the tensor tympani and stapedius muscles simultaneously with complete occlusion of the EAC. According to Boyle's law, the volume of the gas-filled ME cavity at a depth of 1000 m is only 1% of its volume at the surface of the sea. Ascent from such a depth allows the gas in the ME cavity to expand, causing the TM to bulge laterally. This movement is counteracted by a reduction in the blood volume inside the cavernous sinuses, action in the tensor tympani and stapedius muscles and discharge of gas through the Eustachian tube. The presence of a firm, broad-based exostosis in the floor of the EAC lateral to the TM helps to obstruct the EAC.

MR imaging of blood flows in the cavernous sinus.

To evaluate blood flows in the cavernous sinus (CS), seven normal CSs and a postmortem CS were evaluated using T1-weighted spin echo sequences. After the noncontrast study, contrast study with Gd-DTPA was performed in all cases except the postmortem one. In the normal CSs, arterial flows of the intracavernous carotid artery (ICA) were disclosed as no-signal areas in the noncontrast study and were not enhanced with Gd-DTPA. Most venous flows in the CS were seen as low-intensity areas in the noncontrast study and were markedly enhanced with Gd-DTPA. However, these low-intensity areas were heterogeneous in intensity and several were higher and lower in intensity compared with most venous spaces. In the postmortem case, the CS showed homogeneous low intensity due to the stasis of blood flow. It was thought that the heterogeneous appearance of venous spaces in the normal CSs was due to flow-related phenomena. This heterogeneous pattern of signal intensity suggested the distribution of flow velocities. MR demonstrated both arterial and venous flows, and this was facilitated by Gd-DTPA. MR is a promising modality for the demonstration of blood flows in the CS.

[Control and regulation of the blood circulation in the vertebro-basilar system. Review of the literature]. / Contrôle e regulação da circulação sanguínea no sistema vértebro-basilar. Revisão de literatura.

The author establishes an analogy between the control mechanism and regulation of the cerebral blood flow and of protection of the vascular wall of the internal carotid constituted by the conjunction "internal carotid-cavernous sinus" with the group represented by the system "vertebro basilar-transverse occipital sinus or basilar" (an extension of the cavernous sinus) in the regulation and control of the encephalic circulation carried out through this latter vessels, together with the protection of its vascular walls. The author believes to be very difficult to demonstrate in practice the functioning of these mechanisms, but it is very logical and easy to reason about them, to value them and to give the importance and meaning or motive which forcibly they should have and not simply consider them as freaks of nature and bizarre anatomical features.

[The eye and cavernous sinus disorders (author's transl)]. / Oeil et pathologie du sinus caverneux.

The extradural cavernous space lies in relation to the body of the sphenoid and is in direct communication with the orbit through the sphenoidal fissure. Its importance resides in the fact that it is traversed by various elements: internal carotid, and motor and sensory orbit nerves, but also the fundamental venous confluent of the middle stage of the base of the cranium represented by the cavernous sinus. Clinical symptoms of lesions in this region are determined by the respective positions and anatomical relationships of these different structures. Diagnosis can be established by computed tomography, carotid angiography, and orbital phlebography examinations. Whereas cavernous sinus thrombophlebitis is now very rarely observed, "intrinsic" pathological processes detected involve mainly intracavernous carotid aneurysms and carotidocavernous fistulae. The identification of the internal carotid intracavernous collaterals, and the increased knowledge of hemodynamic modifications resulting from carotidocavernous fistulae has led to the development of more appropriate endovascular surgical techniques. These include both elective obstruction of the fistula and the suppression of its various sources of supply. "Extrinsic" lesions of various origins, represented by different tumors of the base of the cranium, and tumors of the nasal and retronasal spaces, particularly cancer of the cavum and metastases, make up the greater part of cavernous syndromes.

Jacques Bénigne Winslow (1669-1760) and the misnomer cavernous sinus.

Sinus cavernosi, or the cavernous sinus, was coined by Jacques Bénigne Winslow in the 18th century. Among the neurosurgeons and the modern-day neuroanatomists, Winslow is mainly known for erroneously using the term cavernous sinus. As the anatomical understanding of the parasellar space advanced during the next 200 years, it was unclear as to why Winslow compared this space in the brain with that of a male reproductive organ (corpus cavernosum). Our primary objective was to study the historical treatise on anatomy written by Winslow in the 18th century and analyze his anatomical dissections and nomenclature for the parasellar compartment. In addition, his pertinent contributions to neuroscience are highlighted in this vignette.

Normal flow signal of the pterygoid plexus on 3T MRA in patients without DAVF of the cavernous sinus.

BACKGROUND AND PURPOSE: Cavernous sinuses and draining dural sinuses or veins are often visualized on 3D TOF MRA images in patients with dural arteriovenous fistulas involving the CS. Flow signals may be seen in the jugular vein and dural sinuses at the skull base on MRA images in healthy participants, however, because of reverse flow. Our purpose was to investigate the prevalence of flow signals in the pterygoid plexus and CS on 3T MRA images in a cohort of participants without DAVFs. MATERIALS AND METHODS: Two radiologists evaluated the flow signals of the PP and CS on 3T MRA images obtained from 406 consecutive participants by using a 5-point scale. In addition, the findings on 3T MRA images were compared with those on digital subtraction angiography images in an additional 171 participants who underwent both examinations. RESULTS: The radiologists identified 110 participants (27.1%; 108 left, 10 right, 8 bilateral) with evidence of flow signals in the PP alone (n = 67) or in both the PP and CS (n = 43). Flow signals were significantly more common in the left PP than in the right PP. In 171 patients who underwent both MRA and DSA, the MRA images showed flow signals in the PP with or without CS in 60 patients; no DAVFs were identified on DSA in any of these patients. CONCLUSIONS: Flow signals are frequently seen in the left PP on 3T MRA images in healthy participants. This finding may be the result of flow reversal and should not be considered to indicate occult DAVF.

The laterocavernous sinus system: venous inflows, venous outflows, and clinical significance.

BACKGROUND: The laterocavernous sinus system is best defined as the entire territory served by the laterocavernous and the superior petrosal sinuses (SPS). METHODS: The laterocavernous sinus is a small but important venous structure located between the two dural layers forming the lateral wall of the cavernous sinus and has been described as one of the principal drainage pathways of the deep and superficial middle cerebral veins. RESULTS: Several disease processes in the head involve the laterocavernous sinus. To evaluate and treat these diseases it is necessary for neuroradiologists not only to know selective angiography and embolization techniques, but also the territory of the laterocavernous sinus and venous watershed between the deep and superficial venous systems. CONCLUSIONS: In the present report the normal angiographic anatomy of the laterocavernous sinus system, its relationship with the deep and superficial venous systems, and its importance in clinical situations are outlined.