gms | German Medical Science

At present, transsphenoidal approaches are characterized by the expanding use of minimally invasive techniques and instrumentation, but this requires improved intraoperative visualization and orientation [1], [2], [3]. In this report, we describe our experience with the complementary use of image guidance during transsphenoidal pituitary surgery in selected cases with recurrent pituitary adenomas and in some complex cases of first-time pituitary surgery.

In preoperative planning process, the adenoma volume and both carotid arteries were segmented in a MRI/CT-3 D dataset (T₁-weighted, 3 D FLASH after Gadolinium) (Figure 1 [Fig. 1] and 2 [Fig. 2]). An optical infrared-based neuronavigation system (Vector Vision, BrainLAB^®, Heimstetten, Germany) was used in all cases for frameless guidance. The patient's head was fixed in a standard Mayfield clamp, and a modified head position with 45-degree head tilt (patient's chin toward the surgeon) was used. A star-shaped reference tool equipped with 3 passive reflective spheres was screwed to the Mayfield adapter clamp, which was fastened to not move in relation to the Mayfield headrest during surgery (Figure 3 [Fig. 3]). The Z-touch infrared device was used for markerless patient registration. The intraoperative accuracy was checked every 10 min by touching with the optically guided instrument easily recognizable bony landmarks (sphenoidal rostrum).

The characteristics of the cases are described in Table 1 [Tab. 1].

A mean calculated accuracy of 1.47±0.4 mm was achieved during co-registration (1.45±0.69 mm for MRI-based NN and 1.53±0.64 mm for CT-based guidance), which is in concordance with the data from the literature, using similar navigational system [2], [5]. 29/30 navigated transsphenoidal procedures were successful; in one case the CT based image guidance failed due to unacceptable registration accuracy.

During the endonasal stage NN was used in lieu of a fluoroscopic C-arm to keep the proper trajectory to the sella turcica in lateral - midline and rostrocaudal direction (useful in 29/29 pts).

In the sphenoidal stage, image guidance was useful to determine depth and trajectory of the approach, as well as to reduce safely working area (in 29/29 pts). Guidance was especially useful in conchal type of sella (in 3/3 cases), in asymmetrical/atypical microsella, in misleading septal anatomy of the sphenoid sinus (in 7/9 pts) and in patients where anatomical landmarks were obscured by tumour or previous surgery (8/9 cases). In transsphenoidal re-operations for recurrent and residual tumours with invaded and/or distorted perisellar space, detailed anatomical knowledge of the position of intracavernous structures is extremely important.

During intrasellar instrumentation image guidance was helpful locating exactly microadenoma. In macroadenomas however, where in the process of tumour resection descensus of the sellar diaphragm or the intracranially buldging tumour capsule occurs, its localization reliability has to be questioned. Similar to Kreutzer et al. [6] we consider the preoperative colour segmentation of the perisellar vascular key structures very helpful in patients with small and asymmetrical sella, in complex and misleading sphenoidal sinus anatomy and during reoperations on aggressive adenomas with CS invasion [7].

The NN control on the trajectory and position of our instruments in relation to the tumor and the surrounding delicate structures (Figure 4 [Fig. 4] and Figure 5 [Fig. 5]) decreases the risk of inadvertent damage to vital parasellar structures [4].

Although in many routine cases of first-time pituitary surgery image guidance is not an absolute necessity, it certainly can be helpful in some occasions:

• In transsphenoidal reoperations of residual and/or recurrent adenomas it allows safely accurate surgeon's orientation toward the sellar confines and perisellar structures;
• In misleading anatomy of the sphenoidal sinus, in narrow, asymmetrical and conchal sella and
• In excentric parasellar adenoma growth for better control of the position of the intracavernous carotid artery.