Microsurgical anatomy of the superficial veins of the cerebrum

Three-dimensional finite element analysis of subdural hematoma

BACKGROUND

Head motion, an important factor in acute subdural hematoma (ASDH), can be broken down into translational and rotational elements. We used three-dimensional finite element analysis to examine the thresholds of angular and tangential acceleration required to tear bridging veins in humans during head impact.

METHODS

The lengths of midsagittal and parasagittal bridging veins were calculated first. To assess the effect of translational and rotational acceleration, the strain of each vein was then computed under three different motions. The threshold of ASDH was expressed in terms of tangential and rotational acceleration.

RESULTS

Deformation-angle histories of the midsagittal and parasagittal bridging veins showed that veins that drain forward into the superior sinus at a 130-degree angle incurred the greatest stretch strain during occipital impact. In the midsagittal plane, pure rotation induced greater stretch strain on these veins (14.4%) than pure translation (2.5%) or combined translation and rotation motion (10.4%). A tangential acceleration of 3,912.9 G or an angular acceleration of 71.2 krad/s2 seemed to approximate the threshold for ASDH in the human midsagittal plane, whereas 5,010.9 G and 97.4 krad/s2 approximated the threshold in the parasagittal plane.

CONCLUSION

Impact direction and orientation of bridging veins are both important factors in ASDH. Threshold criteria for ASDH can be expressed in terms of tangential and rotational acceleration.

Noninvasive assessment of the elastance and reserve capacity of the craniovertebral contents via flow velocity measurements in the straight sinus by TCD during body tilting test

Invasive recording of intracranial pressure (ICP) changes during cerebrospinal fluid (CSF) infusion-drainage tests have been used to estimate elastance and reserve capacity of craniovertebral contents. The increase in ICP and its pulse-related oscillations lead to "cuff constriction" of cerebral veins. The purpose of this study is noninvasive assessment of elastance and reserve capacity of craniovertebral contents (RCCC) by measurement of flow velocity (FV) in the straight sinus by transcranial Doppler (TCD) during body tilt tests, which cause changes in ICP. The study was performed in 14 healthy volunteers (age 12-49 y, 6 men) and 32 patients with Intracranial Hypertension (IH) (Benign Intracranial Hypertension, n = 14; Brain Tumors, n = 18). The straight sinus was insonated through the occipital window during body tilt tests (BTT). Tilt table position was changed gradually from head up (+75 degrees) to head down (-45 degrees). It was established that systolic flow velocity and amplitude of FV pulsations (Amp) in horizontal position in patients is usually higher than in healthy volunteers. We found that reserve capacity of craniovertebral contents in patients with IH was usually exhausted. Elastance in patients was usually significantly higher than in healthy volunteers. Evaluation of cerebral venous circulation during body tilt tests clearly differs between the patients with IH and the healthy volunteers. The degree of this difference depends on the localization and character of the pathologic process.

A new technique for the assessment of the draining area of a cerebral vein

BACKGROUND

At present, it is not exactly clear which vein is allocated for drainage of blood to a particular area of the human brain. Knowledge of these draining areas is very important for the understanding of occlusive venous diseases. A method was developed that offers the possibility to investigate the draining area of a cerebral vein, with the help of an animal model.

METHODS

Brains of sacrificed rabbits are removed and are anterogradely perfused with a coloring matter. Then a vein chosen at random is occluded and anterograde perfusion is restarted using another coloring substance. The working hypothesis is that the part of the brain that is solely dependent for its drainage of blood upon the occluded vein (the draining area of the vein) will show a deficit in staining after the second perfusion. RESULTS Using the abovementioned technique, no filling defect was seen if a vein was occluded near its entrance into the sinus (N = 8) or at a single point over the cortex (N = 7). If a longer trajectory (10-14 mm.) was obstructed, a clear staining defect was seen in 13 out of 16 hemispheres; the three remaining cases seemed to be technical failures.

CONCLUSION

A new method is described to investigate the draining area of a cerebral vein. Although the validity of the method is proven in an animal model, it seems a good technique for investigation of human brains postmortem. Application of this technique will contribute to the understanding of the pathophysiology of venous diseases and also elucidate the role of the venous anastomotic pathways.

Operative approach to mediosuperior cerebellar tumors: occipital interhemispheric transtentorial approach

BACKGROUND

The transtentorial approach is well known as an approach to the pineal region. We have modified this approach for mediosuperior cerebellar tumors.

METHODS

We describe six cases of tumor excision in this region using an occipital interhemispheric transtentorial approach.

RESULTS

The lesions were easily accessible and the tumor was totally removed by this modified approach in all cases. Transient visual field disturbance with spontaneous recovery occurred in two patients. The lateral margin of the tumor was accessed easily up to 35 mm from the midline on the operative side and up to 17 mm from the midline on the contralateral side.

CONCLUSION

This approach proved to be very useful for mediosuperior lesions of the cerebellum, without causing any neural structural damage, and allowed for a wider operative field.

Combining endovascular and neurosurgical treatments of high-risk dural arteriovenous fistulas in the lateral sinus and the confluence of the sinuses

OBJECT

The authors describe the use of a systemic approach to treat dural arteriovenous fistulas (DAVFs) in the lateral sinus and the confluence of sinuses in 17 patients who presented with signs and symptoms related to intracranial hemorrhage, infarction, and diffuse brain swelling.

METHODS

Angiographic examination revealed three different types of DAVFs in these high-risk patients: 1) extremely high flow DAVF not associated with sinus occlusion or leptomeningeal retrograde venous drainage (LRVD); 2) localized DAVF with exclusive LRVD and without sinus occlusion; and 3) diffuse DAVF with sinus occlusion and LRVD. Because of the complex nature of these lesions, the authors adopted a staged protocol in which they combined endovascular and surgical treatments.

CONCLUSIONS

The authors believe that by close collaboration between endovascular therapists and vascular neurosurgeons, high-risk DAVFs in the lateral sinus and the confluence of sinuses can be successfully managed without treatment-related morbidity and mortality.

Analysis of CO2 vasomotor reactivity and vessel diameter changes by simultaneous venous and arterial Doppler recordings

BACKGROUND AND PURPOSE

The use of flow velocity changes in the middle cerebral artery (MCA) measured by Doppler techniques as an index of corresponding cerebral blood flow (CBF) changes is based on the assumption that the insonated arterial diameter remains stable. The postulate of unchanging vessel calibers during CBF changes, however, is still under debate. We performed simultaneous measurements of arterial and venous blood flow velocities by transcranial Doppler ultrasound during various stages of hypercapnia to analyze diameter changes in the insonated vessels by comparing differences in the vasomotor reactivity.

METHODS

Simultaneous Doppler recordings of 1 MCA and of a contralateral venous vessel thought to represent the sphenoparietal sinus (SPS) were carried out with a pair of 2-MHz range-gated transducers in 16 young healthy subjects during variations of end-tidal PaCO2.

RESULTS

During hypercapnia the mean blood flow velocity of the MCA rose from 62. 5+/-10.2 to a maximum of 99+/-12.2 cm/s (vasomotor reactivity of 60. 1+/-17.3%). The corresponding values in the SPS were significantly higher (P<0.001), revealing a rise from 17.8+/-5.7 to 34.9+/-14.3 cm/s (vasomotor reactivity of 91.4+/-25.9%). Exponential and linear regression analyses revealed an identical high correlation (r2=0.97 and 0.98 for the MCA and SPS, respectively). Slopes were 0.034+/-0. 01 on the arterial and 0.048+/-0.01 on the venous side. The CO2 reactivity (percentage per mm Hg, EtCO2) was found to be 4.5+/-1%/mm Hg in the MCA and 6.8+/-1.5%/mm Hg in the SPS. This difference indicates a vasodilation of the MCA in comparison to the venous vessel.

CONCLUSIONS

We have demonstrated a different reaction pattern between intracranial venous and arterial vessels related to end-tidal CO2. Relating the flow velocities to the square of the vessel diameter and assuming a global rise of CBF and not extensible sinus walls, our results indicate that the MCA undergoes a vasodilation of 9.5+/-7% in maximal hypercapnia.

Reconstruction of the vein of Labbé by using a short saphenous vein bypass graft. Technical note

Protection of the vein of Labbé is a significant concern during surgery that involves retraction of the temporal lobe. A cranial base surgical approach, especially one via the presigmoid-petrosal route, carries considerable risk to this venous complex. A case is presented in which a large dominant vein of Labbé was injured during resection of a petroclival meningioma. This vein drained all the sylvian venous circulation as well as the lateral temporal surface; no connection to another venous system was noted. The vein was successfully reconstructed using a short saphenous vein bypass graft. Significant complications could have occurred without this reconstruction. The technique and benefits of this type of reconstruction are discussed.

Tentorial venous sinuses: an anatomic study

OBJECTIVE

Certain neurosurgical procedures require sectioning of the tentorium cerebelli. The presence of venous sinuses within the tentorium makes these procedures difficult. The aim of this study was to investigate the incidence, size, location, configuration, and pattern of venous drainage of these sinuses.

METHODS

The tentorium cerebelli was studied in 80 fresh cadavers. After the skull cap and the supratentorial portion of the brain were removed, the tentorium was inspected for the presence of venous sinuses. Their location, size, configuration, and pattern of venous drainage were noted. Subsequently, the infratentorial structures were removed via the tentorial incisura. The tentorial sinuses were again studied. In certain cases, the sinus was opened and a probe passed inside to confirm its presence.

RESULTS

The tentorium cerebelli was revealed to contain sinuses in 86% of the cadavers. These sinuses were classified into the following three types: Type I sinuses constituted 25% of the total and were most often located in the medial one-third of the tentorium. They were larger than the other types, frequently occurring with a branching "stag-horn" configuration and a tendency to drain into the straight sinus, the torcular herophili, and the medial one-third of the transverse sinus. Type II sinuses constituted 25% of the total and were most often located in the lateral one-third of the tentorium. They were smaller than the other types, and tended to drain into the duction of the transverse sinus and superior petrosal sinus and into the lateral one-third of the transverse sinus. Type III sinuses constituted 50% of the total and were located in the medial one-third of the tentorium. Their size ranged from small to medium. Unlike Type I sinuses, no branching pattern was observed. These sinuses tended to drain into the straight sinus, the torcular herophili, and the medial one-third of the transverse sinus. In the present study, the medial one-third of the tentorium was observed to be the most vascular part. No venous sinus was observed in the anterior part of the tentorium.

CONCLUSION

Venous sinuses are common in the tentorium cerebelli. In this study, they were observed in 86% of the cases. They can be classified into three types, based on their location, size, configuration, and pattern of drainage. The medial one-third of the tentorium is the most vascular part. A knowledge of these sinuses may be helpful while sectioning the tentorium. The importance of these sinuses in treating vascular and neoplastic diseases of the brain is highlighted. A brief review of the embryology of these sinuses is also presented.

Venous drainage of the inferolateral temporal lobe in relationship to transtemporal/transtentorial approaches to the cranial base

OBJECTIVE

Intimate to the application of lateral transtemporal approaches to the cranial base are the identification, manipulation, and/or the sacrifice of the venous anatomy of the inferolateral temporal lobe and the superior petrosal sinus and the transection of the tentorium. This study demonstrates the relationship and variability of the venous drainage of the lateral and inferior surfaces of the temporal lobe.

METHODS

Twenty-one specially prepared, injected cadaver specimens yielded 40 temporal lobes for examination. The venous systems in these specimens were traced from their origins on the temporal lobe (venous drainage complexes) to the transverse/petrosal sinuses, and the geometry of these venous complexes (venous configuration) was noted. The measurements of each complex's entry to the sinuses were noted.

RESULTS

Four distinct venous drainage complexes were identified: 1) the lateral complex, 2) the anteroinferior complex, 3) the medial-inferior complex, and 4) the posteroinferior complex. Three basic venous configurations were found: 1) the candelabra of veins uniting to form one large draining vein, 2) multiple independent draining veins, and 3) venous lakes running in the tentorium before entering the sinuses. The lateral complex, incorporating the classic "vein of Labbé," was present in 100% of the specimens. However, in the majority of cases, it did not represent the dominant venous drainage of the lateral and inferior surfaces of the temporal lobe.

CONCLUSION

An understanding of the complexity and diversity of the venous drainage complexes and their configurations is necessary to avoid venous complications during lateral cranial base surgery.

Correlation between venous stump pressure and brain damage after cortical vein occlusion: an experimental study

A canine model of cortical vein occlusion was used to evaluate whether data obtained from monitoring venous stump pressure could help predict cerebral infarction after venous obstruction. Following bilateral parasagittal craniotomy, the cortical vein in each hemisphere was temporarily occluded and the increase in pressure was directly measured. Permanent venous obstruction was subsequently produced, and parenchymal brain damage 24 hours later was classified as: Stage 0, no parenchymal damage; Stage I, mild edema; Stage II, moderate parenchymal edema and/or ischemic changes in neurons; and Stage III, moderate-to-severe hemorrhage. The histological stages correlated closely with the rise in venous pressure: mean pressure increases (+/- standard deviation) were 5.5 +/- 2.9 mm Hg in hemispheres graded as Stage 0 (12 hemispheres), 7.7 +/- 3.2 mm Hg in those graded as Stage I (five), 11.2 +/- 4.1 mm Hg in those classed as Stage II (five), and 16.4 +/- 5 in those categorized as Stage III (seven). There were significant differences between Stages 0 and II (p < 0.01) and between Stages 0 and III (p < 0.001). Disruption of the blood-brain barrier as indicated by extravasation of Evans blue dye correlated well with the pressure increment. These results may indicate the threshold for injury after cortical venous occlusion. Venous stump pressure measurements obtained during a test occlusion may be a useful adjunct in predicting brain damage and may be helpful for intraoperative vessel selection for venous resection.

Anatomic details of intradural channels in the parasagittal dura: a possible pathway for flow of cerebrospinal fluid

OBJECTIVE

The absorption of cerebrospinal fluid occurs primarily by means of arachnoid granulations (AG) in the superior sagittal sinus (SSS) and the lacunae laterales (LL) in the parasagittal dura. Previous descriptions of this region suggest a network of intradural channels, but finer details of extent and relationship between channels and AG were not addressed. Therefore, we undertook an anatomic study of cadaveric parasagittal dura.

METHODS

The SSS and parasagittal dura of 20 formalin-fixed adult cadavers and 15 autopsy specimens from patients ranging in age from 18 weeks of gestation to 80 years were studied by use of a light microscope, a scanning electron microscope, and corrosion casting. Intradural injections into the parasagittal region were performed in two formalin-fixed and four autopsy specimens from adults by use of normal saline and corrosion casting.

RESULTS

Extensive networks of intradural channels from 0.02 to 2.0 mm in diameter were noted in all of the specimens. Channels either were connected to the SSS at intervals along the side wall or drained directly into the LL, which extended up to 3 cm from midline. Channels lined with endothelium stained positive for Factor VIII, as did the endothelium of the LL and SSS. In some places, the network of channels seemed to coalesce to form LL. The underside of the dura was coarse and trabeculated where the channels were abundant, and AG were interdigitated between these trabeculae. In regions of the dura where channels were sparse or absent, the dural underside was smooth and lacked AG. Underlying cortical veins opened directly into the SSS and were unrelated to intradural channels. Intradural parasagittal injections from the epidural side accessed the SSS by way of channels using pressures between 0 and 20 cm H2O at 1.5 ml/min.

CONCLUSION

These channels may represent a pathway for the flow of cerebrospinal fluid from AG to the SSS.

Anatomic study of anterior frontal cortical bridging veins with special reference to the frontopolar vein

Anatomic variations of the frontopolar vein were investigated in 21 cadaver brains to improve the preservation rate of this vein in interhemispheric surgery for anterior communicating aneurysms. Most of the frontopolar vein has been considered to drain the outer convex side of the frontal lobe, but in reality, the area of its venous drainage was found to cover a large part of the frontal lobe, including its medial and basal surfaces. This observation suggests that sacrifice of the vein during surgery carries a risk of venous infarction. Therefore, care must be taken to not injure the vein during surgery. The mean distance between the frontopolar vein and the most anterior point of the frontal lobe was 31.1 mm. Although the vein became smaller close to the frontal tip, the mean diameter of the vein was 1.9 mm. Morphologically, approximately two-thirds of the frontopolar veins was found to have a "main trunk." The frontopolar vein can be spared during surgery by using a flexible surgical technique incorporating vein dissection or additional craniotomy.

The variations of Sylvian veins and cisterns in anterior circulation aneurysms. An operative study

The anatomical variations of Sylvian vein and cistern were investigated during the pterional approach in 230 patients with 276 aneurysms of anterior circulation arteries, that were operated on at the Neurosurgical Department of Atatürk University Medical School. Erzurum, Türkiye. All patients underwent radical surgery for aneurysm by the right or left pterional approach. The findings were recorded during surgical intervention and observed through the slides and videotapes of the operations. In our study, we surgically classified the variations of the Sylvian vein, according to its branching and draining patterns. Type I: The fronto-orbital (frontosylvian), fronto-parietal (parietosylvian) and anterior temporal (temporosylvian) veins drain into one sylvian vein. Type II: Two superficial Sylvian veins with separated basal vein draining into the sphenoparietal and Rosenthal's basal vein. Type III: Two superficial Sylvian veins draining into the sphenoparietal and the superior petrosal veins. Type IV: Hypoplastic superficial Sylvian vein and the deep one. Four types of Sylvian vein variations were defined as follows. The Type I was seen in 45% (n = 103), the Type II was found in 29% (n = 67), Type III was recorded in 15% (n = 34) and Type IV, or hypoplastic and deep form was discovered in 11% (n = 26) of patients. The course of the Sylvian vein was on the temporal side (Temporal Coursing) in 70 percent of the cases (n = 160), on the frontal side (Frontal Coursing) in 19% of the patients (n = 45) and in 8 percent of the cases (n = 18) in the deep localization (Deep Coursing). Only 3 percent of the cases (n = 7) showed a mixed course. The variations of the Sylvian cisterns were classified into three types, according to the relationships between the lateral fronto-orbital gyrus and the superior temporal gyrus. In Sylvian Type, the frontal and temporal lobes are loosely (Sylvian Type A, Large) or tightly (Sylvian Type B, Close and Narrow) approximated on the surface thereby covering the area of the Sylvian cistern. In frontal type, the proximal, part of the lateral fronto-orbital gyrus herniated into the temporal lobe. In temporal type, the proximal part of the superior temporal gyrus hemiated into the lateral fronto-orbital gyrus. The variations of the Sylvian cisterns in 230 patients were as follows: in 31% (n = 71) Sylvian Type A, in 21% (n = 48) Sylvian Type B, in 34% (n = 78) Frontal Type, and in 14% (n = 33) Temporal Type. We concluded that venous perfusion disorder of the brain is the most important factor during the pterional approach. Careful intraoperative assessment and protection of the Sylvian vein, which is a surgical pitfall, is an indispensable part of the operation. The recognition of the anatomical variations of the Sylvian vein and cistern, and the detailed knowledge of the microvascular relationships at that level will allow the neurosurgeon to construct a better and safter microdissection plan, to save time and can prevent postoperative neurological deficits.

Anatomical and technical aspects of the contralateral approach for multiple aneurysms

Microsurgery of multiple aneurysms is still a controversial subject. In order to avoid the risk of rebleeding and the consequent increase in morbidity in such cases all aneurysms or at least as many aneurysms as possible should be treated in the first operative procedure. To reach that goal aneurysms located on the contralateral side should also be considered for clipping during the first operation. Between 1984 and 1994 a series of 51 patients harboring multiple aneurysms of which 55 aneurysms were located on the contralateral side of the craniotomy were operated at our institution. No mortality or morbidity could be directly ascribed to the aneurysm that was clipped contralaterally. Based on that series we have described the anatomical features, technical aspects and surgical difficulties of approaching bilateral aneurysms through the same craniotomy.

Obstruction of the superior sagittal sinus caused by parasagittal meningiomas: the role of collateral venous pathways

The authors present studies of eight patients who had obstruction of the superior sagittal sinus caused by parasagittal meningioma. The results indicate that meningeal veins and end-to-end anastomoses of the superficial veins of the cerebrum play important roles as collateral venous pathways. This assessment suggests that, in patients with obstruction of the superior sagittal sinus, venous phase angiography should be carefully interpreted before surgery is attempted for parasagittal meningiomas.

Basal interfalcine approach through a frontal sinusotomy with vein and nerve preservation. Technical note

The authors describe a new method for a frontal interhemispheric approach when treating craniopharyngiomas of the third ventricle or anterior communicating artery aneurysms. This technique ensures preservation of the bridging veins and the olfactory nerves. This "basal interfalcine approach" involves a craniotomy in the centrobasal portion of the frontal bone (the frontal sinus), removal of the inner tables and the crista galli, and splitting the basal portion of the falx into two leaves, through which the basal interhemispheric fissure is opened. The olfactory nerves are protected by the leaves of the falx, and the bridging veins are preserved because the approach is low enough to spare them. The surgical techniques are described together with a unilateral variation of this approach. The significance of preserving the bridging veins is discussed in connection with avoidance of postoperative contusional hemorrhage.

The termination of the vein of "Labbé" and its microsurgical significance

Information about the termination of the inferior anastomotic vein of Labbé is of crucial importance in the subtemporal neurosurgical approach and its modifications. An intradural course has been observed in all cases. The vein of Labbé reaches in 3/4th the anterior third of the transverse sinus, in 73% of all cases tracing a so-called tentorial sinus. By dissecting the vein of Labbé out of its dural bed and shifting its fixation point, microsurgical access is facilitated considerably.

Microsurgical anatomy of the tentorial sinuses

Variations of the tentorial sinus of cadaver cerebellar tentoria were examined under a surgical microscope. The tentorial sinuses were classified into four groups: Group I, in which the sinus received venous blood from the cerebral hemisphere; Group II, in which the sinus drains the cerebellum; Groups III, in which the sinus originates in the tentorium itself; and Group IV, in which the sinus originates from a vein bridging to the tentorial free edge. The tentorial sinuses of Groups I and II were frequently located in the posterior portion of the tentorium. The sinuses of Group I were short and most frequently present in the lateral portion of the tentorium. The tentorial sinuses of Group II, which were usually large and drained into the dural sinuses near the torcular, were separated into five subtypes according to the draining veins and direction of termination. The tentorial sinuses of Groups III and IV were located near the tentorial free edge or the straight sinus. The draining patterns of the tentorial sinuses and their draining veins (so-called "bridging veins") were present in most cases. Knowledge of this anatomy can benefit the neurosurgeon carrying out repair near or on the cerebellar tentorium.

The trans-cerebral veins: normal and non-pathologic angiographic aspects

The trans-cerebral v. have long been described, but there is little or no knowledge of their function and dysfunction. They are the site of fundamental interchange across the blood-brain barrier, a unique process within the organism. Two systems can be structurally distinguished: the venous system draining the white matter and the trans-cerebral anastomotic system. The former seems to be associated with the nutrition and drainage of the parenchyma, and is rendered visible at angiography by anatomic variations based on developmental venous anomalies. The anastomotic trans-cerebral ventriculo-cortical system seems concerned with the regulation of reabsorption of the cerebrospinal fluid. It is visualized only in exceptional situations where an increased flow (arteriovenous shunt) is combined with obstruction of the normal routes of venous drainage and collateral circulation. It usually functions in the ventriculo-cortical direction. No specific dysfunction of this system is currently recognized.

Insensitivity of tensile failure properties of human bridging veins to strain rate: implications in biomechanics of subdural hematoma

The effects of strain rate on tensile failure properties of human parasagittal bridging veins were studied in eight unembalmed cadavers. While bathed in physiological saline at 37 degrees C, the intact vessel was stretched axially by a servo-controlled hydraulic testing machine at either a low strain rate of 0.1-2.5 s-1 or a high rate of 100-250 s-1. The mean ultimate stretch ratios for low and high strain rates, respectively, were 1.51 +/- 0.24 (S.D. n = 29) and 1.55 +/- 0.15 (n = 34), and the ultimate stresses were 3.24 +/- 1.65 (n = 17) and 3.42 +/- 1.38 MPa (n = 20). Neither difference between strain rates was significant (p greater than 0.45). Thus, our results do not support the hypothesis that sensitivity of the ultimate strain of bridging veins to strain rate explains the acceleration tolerance data for subdural hematoma in primates [Gennarelli, R. A. and Thibault, L. E. (1982) Biomechanics of acute subdural hematoma. J. Trauma 22, 680-686].

Acute traumatic vertex epidural haematomas surgically treated

Eleven consecutive cases of acute traumatic vertex epidural haematomas (VEDHs) among 416 epidural haematomas (EDHs) operated on during the same period in the Neurosurgical Clinic of the University of Genoa, are reported. Clinical features, neuroradiological aspects (X-ray, angiography and CT scan) and results are discussed, in order to point out the problems encountered in the diagnosis, expecially due to the mystifying clinical picture and the unsuitability of the axial CT scan in the detection of these lesions. In this series mortality rate was 18%, against 50% reported in the literature.