Journal of Surgery

Introduction

Pilocytic astrocytomas are benign tumors of the central nervous system. Complete surgical resection is associated with a more favorable prognosis. Bond et al. reported that 31% of patients experience tumor recurrence, with a significant difference between those who underwent gross total resection (27%) and those with subtotal resection (73%) [1]. These astrocytomas frequently occur within the brainstem, where complete resection is often challenging due to the tumor’s critical location [2]. When residual tumor tissue remains, management options include observation, radiotherapy, or brachytherapy. Brachytherapy has demonstrated a high response rate and excellent local control, achieving an overall survival rate of 86.2% at 10 years [3]. However, space-occupying cysts develop in approximately 12.8% of patients treated with either resection or brachytherapy.

We present the case of a patient diagnosed in 2004 with a brainstem

tumor following the onset of gait disturbance. After complete resection, no residual tumor was detected. In 2006, a space-occupying cyst developed and was treated with stereotactic drainage. Following recurrent symptomatic cyst formation, additional resections were performed in 2007 and 2008. In 2014, the patient presented with hemifacial pain due to cyst recurrence, which was drained and connected to a subgaleal Rickham reservoir.

In 2019, gait disturbances reappeared as the cyst enlarged; the Rickham reservoir was found to be occluded and was subsequently removed, followed by stereotactic cyst drainage. In 2023, an open surgical resection and fenestration of multiple cysts were performed. Postoperatively, the patient developed a transient hemiparesis and permanent deafness. In June 2025, the pontine cyst recurred once more, resulting in renewed gait impairment (Figure 1).

Figure 1 Space occupying cyst causing gait disturbances.

The patient declined open surgery; therefore, stereotactic aspiration of the cyst was offered as an alternative. Following aspiration, the patient’s condition improved for approximately three months before gait disturbances recurred. To facilitate future management, the placement of a Rickham reservoir was considered. Up to that point, all stereotactic cyst aspirations and the initial Rickham reservoir placement had been performed with the patient in the prone position via a right infratentorial approach. During the most recent open resection, a large infratentorial craniectomy had been performed (Figure 2).

Figure 2 Large bony defect after right suboccipital craniectomy (patient in prone position!).

The most recent cyst aspiration was performed through the existing surgical scar using a stereotactic guide tube to perforate the dura, allowing for minimal dural opening. (Figure 3).

Figure 3 Suboccipital puncture and aspiration of the cyst in June 2025.

Placing the Rickham reservoir ipsilaterally in contact with bone did not provide a stable fixation option. A contralateral infratentorial placement would have traversed the ipsilateral dentate nucleus, as well as the fourth ventricle and the facial nerve nucleus. A contralateral frontal approach, as described by Amundson et al. would have intersected the ipsilateral corticospinal tract [3]. Consequently, we considered whether a transtentorial approach could represent a safe alternative for our patient and conducted a review of the literature to evaluate this option.

Materials and methods

Pubmed and medline analysis

In this study the pubmed and medline databases were analysed using the terms “stereotactic” AND “transtentorial”. All occurring papers were reviewed and included, if both terms really met our criteria.

Stereotactic procedure

The patient was offered the alternative treatment of open fenestration and was informed that there was little to no experience regarding the outcome of this new procedure. Informed consent was obtained. On the day of the procedure, the patients received total intravenous anesthesia and a single shot of 1.5 g cefuroxime. The patient’s head was fixed in a aluminum ring (Precisis AG, Heidelberg, Germany) within a prone position. MR images with 2mm slices and a stereotactic CT were uploaded into the inomed iPS 6.0 software (inomed, Emmendingen, Germany). Several potential trajectories were evaluated to determine the safest surgical approach. A parietal transtentorial route was ultimately selected (Figure 4).

Figure 4 Stereotactic parietal transtentorial approach within the stereotactic CT scan (top) and within the MRI (bottom).

Stereotactic coordinates were established using a Riechert–Mundinger frame (Precisis AG, Heidelberg, Germany) and verified with a stereotactic phantom (Precisis AG, Heidelberg, Germany). The distance from the skull to the tentorium was measured, and a Backlund biopsy needle was advanced along this trajectory.

As the Backlund cannula was unable to perforate the tentorium, the biopsy spiral was utilized. The spiral was gently rotated through the tentorium; however, it could not be retracted to complete the perforation. Therefore, the Backlund needle was rotated around the spiral until the tentorium was successfully penetrated. The spiral was then removed, and the inner component of the Backlund needle was reinserted (Figure 5).

Figure 5 Backlund biopsy needle with inlay (left), with biopsy spiral beginning to exit (middle) and at end position of biopsy spiral (right).

A Rickham reservoir was connected to a 92 mm catheter, which, with its guiding wire, was introduced through a secondary guiding sleeve. The cyst was punctured using the Backlund needle, which was then withdrawn, allowing insertion of the Rickham catheter. The cyst volume was measured by 7 mL. The Rickham reservoir was accessed and aspirated slowly; approximately 7 mL of viscous, yellow, gel-like fluid was evacuated, followed by cerebrospinal fluid, at which point aspiration was discontinued.

The wound was subsequently closed, and an immediate postoperative CT scan was obtained to confirm correct catheter placement and exclude potential complications (Figure 6).

Figure 6 Immediate post-operative CT scan showing correct placement of catheter within the smaller cyst (left) and no adverse event at the breakthrough point of the tentorium, and a good alignment along the planned trajectory (bottom).

Results

Pubmed and medline analysis

The search was done using the NLM Medical subject headings MeSH terms “stereotactic” and “transtentorial” and the Boolean operator “AND”. 32 citations were listed and reviewed. 26 publications covered infratentorial procedures and were excluded. Of the remaining six publications two focused on a transtentorial but transhiatal approach [4,5] (Figure 1).

Figure 7: PRISMA flow diagram of pubmed/ medline research.

Medical subject headings “stereotactic” and “transtentorial” where combined using Boolean operator “AND”. All publications were reviewed and excluded if the topic does not match the topic. Only four publications are relevant.

The first publication is a case report of a cerebellar vermian abscess with was drained successfully. The second publication deals with trapped fourth ventricles in four patients that were treated successfully. The remaining four publications deal with different diseases.

Aung et al. show a case of a stereotactic aspiration of the cystic pontine lesion of a pulmonary adenoma via an occipital transtentorial route using a subgaleal Ommaya reservoir for follow up aspirations [6].

Galanda et al. treated nine patients with cerebral palsy with deep wire electrodes, which were placed trantentorailly directly into the anterior lobe of cerebellum [7].

Garber et al. analysed patients with trapped fourth ventricles. They report 11 patients in which a shunt was place stereotactically from parietal through the tentorium [8].

Turner et al. demonstrated three patients with cystic lesions (Dandy Walker malformation, arachnoid cyst and trapped fourth ventricle) which were treated successfully with a transtentorially placed cysto-peritoneal shunt [9]. A summary of all cases is presented in Table 1.

Table 1 Overview over published cases and our case.