Lateral posterior fossa venous sinus relationships to surface landmarks

BACKGROUND: Knowing the location of the venous sinuses in the combined lateral posterior fossa and lateral cranial base approach is important to prevent their inadvertent injury. The identification of surface landmarks related to these structures is useful in planning such surgical approaches. METHODS: Twelve injected adult cadaver specimens and 10 dried skulls were used to study the relationship of the venous sinuses to various surface anatomic structures. RESULTS: The asterion was not clearly seen in 60% of the studied cadaver sides. The asterion was always clearly seen in the dry skull preparations. The upper margin of the superior nuchal line was found to range from 1.5 mm to 14 mm inferior to the lower margin of the lateral transverse sinus. In 85% of our specimens, the mastoid groove was found to completely overlie the sigmoid sinus. CONCLUSIONS: The asterion was found to be variable in its anatomic relations to other identifiable structures. This variability in relation to other posterior fossa bony landmarks limits its overall usefulness as a consistently stable marker for intracranial structures. The first and most superolateral burr hole for lateral posterior fossa procedures can be safely placed 1 cm below the superior nuchal line and 1 cm medial to the top of the mastoid groove. A burr hole in this location will avoid the transverse and sigmoid sinuses, as well as the transverse-sigmoid junction, yet will be high enough and lateral enough to provide easy exposure of these venous sinuses for all lateral posterior fossa procedures.     

Consideration of the operative indications for posterior fossa venous angiomas

The case of a patient with a venous angioma located in the midline of the posterior fossa and responsible for a cerebellar hemorrhage is reported. The patient had a good recovery after removal of the hematoma. We reviewed this and seven other cases of venous angioma in the posterior fossa reported in the literature. It appears that those venous angiomas that occur in the cerebellar hemisphere and produce a cerebellar hematoma can be successfully removed.     

Quadriplegia following venous air embolism during posterior fossa exploration. A case report

A frequent complication of posterior fossa exploration with the patient in the sitting position is venous air embolism. Spinal cord deficits following such a mishap have rarely been reported. We report a case in which a patient who suffered venous air embolism developed quadriplegia from the C6 level. The mechanisms of passage of air into the arterial system are discussed.     

Stereolithography for posterior fossa cranioplasty

Posterior fossa cranioplasty has been suggested for improvement of neurological symptoms following craniectomy. However, there is no particular recommendation in the literature about techniques for prosthesis manufacture and implantation. We report our experience using rapid prototyping technology and stereolithography for pre-surgical implant design and production of cranioplasties.     

Anaesthesia for posterior fossa surgery

Surgery on the posterior fossa is technically challenging and requires surgical skill and judgement. The anaesthetist through an understanding of the surgeon's problems, the provision of ideal operating conditions, the meticulous monitoring for changes in vital signs and good communication with the surgeon can make a crucial contribution to successful outcome for the patient. The positioning of patients poses particular problems. The prone and lateral positions, together with the supine for transoral surgery, can provide for appropriate access to all parts of the posterior fossa. Traditionally it has been argued that the sitting position offers specific advantages although it creates additional problems for the anaesthetist. In recent years the potential risks of sitting patients up have been extensively investigated and concern has focused in particular on the danger of paradoxical air embolism. Although its safety in recognized centres has been demonstrated, it is clear that this position is now falling out of favour.     

Carotid-cavernous sinus fistula presenting as a posterior fossa mass. Case report.

The authors report a case in which trigeminal neuralgia and hearing loss developed 14 years after a severe head injury. Arteriography demonstrated a carotid-cavernous sinus fistula producing a large venous mass in the posterior fossa.     

Dermoid & epidermoid cysts of the posterior cranial fossa with complete dermal sinus

Riassunto Gli. Aa. discutono i problemi clinici della cisti dermoidi ed epidermoidi della fossa cranica posteriore con seno dermico occipitale, ne espongono i dati morfogenetici e i rilievi anatomici, e passano in rassegna le caratteristiche dei pochi casi finora pubblicati.Espongono una loro osservazione del genere facendone risaltare il decorso clinico, costellato di episodi meningitici acuti subentranti, e le difficoltà dell'estirpazione operatoria.

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Summary The Aa. discuss the clinical problems connected with the development of epidermoids and dermoids of the posterior fossa. Morphogenetical and anatomical features are mentioned, while the cases, which have been published are enumerated and commented upon.A case is described of a child with a dermoid of the posterior fossa (with complete dermal sinus), complicated by repeated bouts of meninigitis, which rendered more difficult operative procedures.

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Zusammenfassung Die Autoren diskutieren die klinischen Probleme derjenigen Dermoide und Epidermoide der hinteren Schädelgrube, die mit einem Zapfen, d. h. mit einer Art Fistelgang mit der Haut in Verbindung stehen. Morphologische und anatomische Daten werden zusammen mit den wenigen bisher im Schrifttum veröffentlichten derartigen Fällen besprochen. Beschreibung eines eigenen Falles, bei dem mehrere meningitische Schübe Schwierigkeiten des Verlaufes und der Exstirpation des Tumors bedingten.

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Resumen Los autores discuten los problemas elínicos relacionados con el desarrollo de los quistes dermoides y epidermoides de la fosa craneal posterior. Se mencionan especialmente los rasgos morfológicos y anatómicos de éstos procesos, efectuandose también una revisión y comentario de los casos publicados en la literatura.Se describe un caso de un niño con un dermoide de la fosa posterior (con un seno dérmico completo) que estuvo complicado por episodios repetidos de meningitis que dificultaron las maniobras operatorias.

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Résumé Les Aa. discutent la Symptomatologie des kystes épidermoïdes et dermoïdes de la fosse postérieure avec ou sans sinus dermique, et décrivent les donnés pathogéniques et anatomiques, tenant compte des cas publiés.Ils exposent un cas personnel de kyste dermoide de la fosse postérieure avec synus occipital complet, qui fut compliqué par des accidents méningés répétés, ce qui engendra des difficultés dans l'extirpation du kyste.

     

Pressure-supported ventilation for posterior fossa operation

To maintain enough gas exchange while using spontaneous respiration as a monitor of the normal brainstem function, we tried pressure-supported ventilation (PSV) with a Servo 900C ventilator (Siemens Elema AB, Sweden) on 12 otherwise healthy patients during posterior fossa operation. Ventilation mode was switched from controlled to PSV after the dura was open uneventfully in all cases but one. With a trigger level of -1 to -2 cm H2O, spontaneous respiration was triggered to start the inspiration. With supporting inspiratory pressure of 4-20 cm H2O, PaCO2 was kept at 31.7-45.9 mm Hg. The ventilatory level could be monitored breath by breath by ventilatory frequency, tidal volume, minute volume, and end-tidal CO2 concentration shown on the ventilator system. Apnea was observed in two cases during surgical manipulation around the brainstem. It was indicated immediately by the ventilator's alarm for decreased expiratory minute volume, and no sign of brainstem dysfunction was observed postoperatively. PSV was useful in maintaining adequate ventilation whereas spontaneous respiration was used as an indicator of normal brainstem function. The alarm system of the ventilator was sensitive enough to detect the surgical invasion of the brainstem at a very early stage.     

Microsurgical posterior fossa exploration for trigeminal neuralgia: a study on 48 cases.

The authors present their experience in the microsurgical treatment of trigeminal neuralgia (TGN). Over the last five years 48 patients were explored and 34 (71 %) underwent microvascular decompression (MVD) for significant arterial or venous conflicts. The remaining 14 patients (29 %) underwent partial sensory rhizotomy (PSR) because of negative intraoperative findings (simple contact or no conflict). Excellent or good immediate outcomes were achieved in 87.5 and 12.5 % of patients, respectively. Of the three severe recurrences observed during the follow-up period (24.7 months; range: 7 - 65 months), two underwent percutaneous microcompression and one posterior fossa reexploration, which revealed teflon-induced recompression. None of the PSR cases experienced incapacitating face numbness. MVD, an extremely effective procedure in the immediate post-operative period, is burdened in the long term by 20 % recurrences, the majority occurring within two years from surgery. We believe that careful intraoperative evaluation of the conflict entity could be the key to achieve a significant reduction of recurrences: overestimation of simple vascular contact of doubtful etiologic relevance, may lead to ineffective decompression and unsatisfactory results. In our opinion PSR should be preferred to percutaneous treatments in cases of negative exploration (contact or no conflict). In accordance with others we observed that section of half or less of the inferolateral "portio major" allows long-lasting pain relief and good preservation of sensory function.     

Freezing-free preservation of human spermatozoa--a pilot study

This study tested a method for maintaining human spermatozoa without freezing for subsequent use in intracytoplasmic sperm injection (ICSI). We demonstrated that human sperm stored in electrolyte-free solution maintain their motility and viability for at least 4 and 6 weeks, respectively. We also have shown that preserved spermatozoa are fully functional in ICSI. Sperm chromosome analysis after injection of human sperm into mouse oocytes revealed that two weeks of storage does not negatively affect sperm DNA integrity. A mouse model was used to analyze the ability of preserved sperm to participate in normal embryogenesis. Mouse sperm preserved in electrolyte-free solution in a similar manner as human sperm maintained motility for up to 3 weeks. When mouse spermatozoa stored for 1 week were injected into the oocytes by ICSI, they yielded normal blastoctysts and normal viable fetuses. The results of the study bear significance for human assisted reproduction technologies (ART) and provide clinicians and infertile patients with a new method that can simplify sperm preparation for ICSI, assisting men who are unable to provide semen on the day of assisted fertilization.     

Venous angiomas of the posterior fossa should be considered as anomalous venous drainage

Venous angioma of the posterior fossa has been described, and the existing literature has been reviewed. The patient presented had a venous angioma located in the pons, and both cerebellar hemispheres and was drained by an enlarged and anatomically anomalous vein within the fourth ventricle. The patient had a "cough headache" and later had signs of cerebellar involvement. A surgical attempt at collapsing the anomalous vein resulted in death in the immediate postoperative period due to venous infarction of the brain stem and cerebellum. Emphasis has been given to the following: 1. "Cough Headache" can be a presenting feature for venous angiomas of the posterior fossa. 2. Venous angiomas of the posterior fossa are developmental anatomic anomalies with enlargement of certain venous structures as a result of inadequate alternative venous drainage. 3. The enlarged vein, which is the pathognomonic feature of venous angiomas, serves a vital function in drainage of blood from structures in the posterior fossa as the usual drainage pathways are inadequate or absent. 4. Operative intervention aimed at resection or collapse of such large veins, which has been successful in treatment of venous angiomas of the frontal lobe, can be disastrous in the treatment of those lesions occurring in the posterior fossa.     

A pilot clinical study of retrograde oxygen persufflation in renal preservation

In vitro studies have shown that calcium channel blockers (CCB) inhibit lectin-induced lymphocyte proliferation. However, no in vivo effects have been documented yet. In this study we evaluated the effects of CCB on in vivo cellular immunity by using contact sensitivity to oxazolone in mice. From 15 to 30 twelve-week-old female C3H mice were randomized into: 0.9 NS (sham), ethanol, CsA, dexamethasone (DXM), verapamil, diltiazem, and nifedipine groups. These study agents were given daily from day 1 to day 9 subcutaneously to the shaved abdominal wall. The mice were sensitized with oxazolone to the abdominal wall on day 2 and challenged with oxazolone on the right ear on day 8. Delayed-type hypersensitivity was measured on day 10 and defined as the difference in thickness between the right (challenged) and left (control) ear of each mouse. The mean DTH of each study group was compared with that of the sham, and the statistical significance was determined by a Student's t test. The percentage of change in DTH from the sham was also calculated as: (mean DTH of study drug group-mean DTH of sham group)/mean DTH of sham group x 100%. A negative value meant a suppressive effect on DTH; a positive value, an enhancing one. The CsA, DXM, and nifedipine all had significant suppressive effects on DTH. Verapamil had a significant enhancing effect. Ethanol and diltiazem had no significant effect. More studies employing other antigens with several other cell-mediated response measurements along with DTH quantification should be done in order to determine the specificity of the immunosuppressive effect of CCB as well as the potential of any calcium antagonist as an adjuvant suppressive agent.     

Clinical study of chronic arachnoiditis in the posterior fossa

Summary A series of 12 cases of chronic arachnoiditis in the posterior fossa is reported.The diagnosis in six patients was established at suboccipital craniectomy which brought about marked improvement in symptoms. The other six were diagnosed as having arachnoiditis in the posterior fossa from the facts that improvement in clinical symptoms was achieved by lumbar air insufflation, which has often been said to be effective in arachnoiditis, and no abnormal findings were revealed by pneumoencephalo-roulette tomography.By investigating the clinical features of these cases, we came to the following conclusions: many cases of this disease have had head trauma or chronic inflammatory disease in the past; the symptoms are apt to occur abruptly, and display repeated remission and aggravation; symptoms originating in the cranial nerves are diversified, and are often bilateral: peripheral vestibular disturbances and retrocochlear hearing losses are observed on neuro-otological examination. In the caloric test especially the patients show canal paresis (CP) on the more impaired side, but none of them appeared to be nonresponsive to the test; lumbar air insufflation is often an effective treatment for this disease; pneumoencephalo-roulette tomography is very useful for diagnosing pathological changes in the posterior fossa.     

Pneumocephalus and tension pneumocephalus after posterior fossa surgery in the sitting position: A prospective study

Summary Thirty patients subjected to posterior fossa surgery in the sitting position were evaluated postoperatively by CT scans in order to assess the true incidence of pneumocephalus and subsequent development, if any, of tension pneumocephalus. This prospective survey shows that the postoperative incidence of intracranial air was 100%, while no progression towards tension pneumocephalus producing severe neurological deterioration was observed. It can thus be claimed that, although the sitting position may favour the development of tension pneumocephalus also other factors contribute to its pathogenesis. Finally, neither nitrous oxide nor temperature play any significant role in the development of this complication.