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Background: Chronic subdural hematomas are well delineated collections of fluid (blood) between the dura mater and the arachnoid space. Two types of encapsulated chronic subdural hematoma can be distinguished: the nonseptated and the septated form. The nonseptated form can be treated easily using the burrhole-drainage method, whereas treatment of septated chronic subdural hematoma remains a therapeutical problem. The main problem is the division of the hematoma by neomembranes into compartments, which hinder the efflux of the hematoma fluid through one or two burrholes., Methods: Since 1991 we have operated on 14 patients with septated subdural hematoma using flexible steerable endoscopes through a burrhole approach. The flexible endoscopes are fixed and guided with the help of the Marburg Neuroendoscopy Fixation and Guiding System. For resection of neomembranes small microscissors or microforceps were used. This technique avoids blunt rupture of the membranes which may cause bleeding. A closed drainage system is applied temporarily to guarantee the efflux of the remaining hematoma., Results: From January 1991 to May 1994, 14 patients with the septated variant of chronic subdural hematoma were operated on using the endoscopic technique. After the neuroendoscopic intervention 12 patients had a sufficient or complete hematoma evacuation. One patient had to be operated on a second time, and there was one postoperative subdural infection. Long term follow up of all patients shows no recurrence of the subdural hematoma., Conclusion: Treatment of membraneous septated CSH using an endoscopic operative technique combined with the application of a closed drainage system is a minimally invasive method and a therapeutic alternative to the craniostomy-membranectomy technique.

Stereotactic endoscopic techniques are extremely helpful in diagnosis and therapy of cystic intracerebral space occupying lesions. Acute space occupying lesions can be managed effectively and without major tissue traumatization. Up to now we have operated on more than 70 cystic intracerebral space occupying lesions with a stereotactic endoscopic technique. The main diagnoses were colloid cysts, cystic craniopharyngeoma, arachnoidal and pineal cysts. In must be stressed that in cystic anaplastic astrocytomas and glioblastomas as well as metastases only an acute inner cerebral decompression can be achieved by neuroendoscopic techniques in combination with the application of reservoir systems. In benign parenchymal or intraventricular cysts neuroendoscopic intervention is performed for definitive treatment. The results are overall encouraging. There was no operative mortality and operative morbidity was below 3%. Postoperative follow-up in patients with benign cysts showed no evidence of recurrence.

Treatment of brain abscess is still a subject of controversy. Craniotomy with primary extirpation and resection of the abscess membrane, burrhole craniotomy with puncture or insertion of a drain, marsupialization, or stereotactic aspiration are different therapeutic approaches. As a consequence of our experiences and results with neuro-endoscopic interventions we have introduced endoscopic stereotactic techniques in brain abscess treatment. Seven patients with brain abscesses were operated on stereotactically using an endoscope. In all cases the abscess contents were aspirated, while the abscess membrane was left in situ. The patients received postoperative antibiotic therapy according to microbial diagnosis. The longest follow-up period was 48 months. Six patients showed a marked improvement of neurological deficit after treatment. One patient died from sepsis caused by a bacterial endocarditis. The results emphasize that endoscopic stereotactic technique as a minimally invasive neurosurgical method can also be used for treatment of brain abscess.

In 1989 we introduced "endoscopic stereotaxy" as a new operative procedure into neurosurgery. This technique was first scheduled to optimize stereotactic biopsy. In its further development it proved to be effective for other indications. We choose the term "Minimal Invasive (Endoscopic) Neurosurgery (MIEN)" for these interventions. Minimal invasive endoscopic techniques are applied preferably for diagnostic and therapeutic interventions on preformed or pathological cavities of the central nervous system. The indications are, endoscopic-stereotactic biopsy of space-occupying lesions, ventriculoscopy and endoscopic ventriculostomy in diagnosis and treatment of hydrocephalus, endoscopic evacuation of cystic space occupying lesions, endoscopic evacuation of intracerebral haematoma, endoscopic evacuation of septated chronic subdural haematoma, endoscopic evacuation of subacute or chronic brain abscesses, endocavitary syringostomy. Our results with minimal invasive endoscopic interventions for different indications are encouraging when compared to conventional microsurgical techniques. We have performed more than 300 minimal invasive endoscopic interventions. The mortality rate was below 1%, the operative morbidity was below 2%.

42 cadaver brains in situ were examined endoscopically to work out topographical anatomical landmarks for orientation. The endoscopic route from the chosen precoronal trepanation point to the defined ventricular landmarks has been measured in 22 cases. The identification and measurements of the anatomical landmarks are helpful for safe and atraumatic endoscopical navigation within the ventricular system. Furthermore this article describes and discusses cerebral lesions during ventriculoscopy.

The term "minimally invasive neurosurgery" (MIN) is defined and the present indications for MIN are described. They include endoscopic stereotactic interventions, endoscopic evacuations of chronic subdural haematomas and intracerebral mass-haemorrhages, endoscopic spinal and ventriculoscopic procedures. The advantages compared to conventional diagnostic and therapeutic neurosurgical approaches consist of less operative risk and reduced tissue-traumatization. Endoscopy makes interventions under (real-time) conditions possible. The operative stress for the patient is minimized.

The term "midline tumour" is defined partly from the topographic and from the pathogenetic point of view. Problems of modern imagegenerating procedures in establishing the diagnosis of cerebral midline lesions are described. The role of stereotactic diagnostic and therapeutic interventions is emphasized. Stereotactic brain tumour biopsy, installation of shunts and reservoirs under visual control are performed. Interstitial radiotherapy is carried out for low-grade gliomas. As an important innovation, stereotactic procedures are combined with endoscopic techniques. Particular diagnostic and therapeutic difficulties of typical midline tumours such as craniopharyngeoma, germinoma, glioma and primary cerebral lymphoma as a local extension are discussed. A reasonable concept in diagnosis and therapy of cerebral midline lesions is proposed.

A new prototype of an endoscope for stereotactic interventions is described. This endoscope is adapted to the Mundinger-Birg stereotactic system. Stereotactic endoscopic procedures are carried out for brain-tumour-biopsy as well as for evacuation of haematomas, brain-cysts and abscesses. Ventriculoscopy is performed on hydrocephalus and biopsy of ventricle-relating tumours. One-year experience with stereotactic endoscopy is reviewed.