Minimally Invasive Approaches to the Pineal Region

The present review assesses how to make pineal surgery, refined over decades, better, ie, less invasive, while still respecting this delicate region, and achieving anatomic and oncologic goals. An explication of anatomic principles of this region, and some basic surgical principles of keyhole surgery are provided to further assist those interested in minimizing surgical impact during pineal surgery. Although this review, for the sake of brevity, focuses on the infratentorial-supracerebellar approach, many of these principles can be adapted to other approaches, such as the occipital transtentorial, without excessive imagination.

The pineal-tectal region is an anatomically challenging region to operate in safely. Deeply situated in the brain, it is bounded by and guarded by several critical structures, namely the galenic venous system, the superior cerebellar artery, the 4th nerve, the thalamus, and the midbrain. The tentorium is sharply upsloping and the tentorial cerebellar surface is conformal to this slope, with the apex of the vermis, the culmen, tightly fitting in the apical tentorial cleft, and blocking simple access to the pineal region through a direct approach. It was only through adoption of the operating microscope and the sitting position that the infratentorial-supracerebellar approach to the pineal region began to be widely used to directly attack pineal tumors with good outcomes and minimal morbidity.

The present review assesses possible strategies on how to make this significant advance, refined over decades, better, ie, less invasive, while still respecting this delicate region, and achieving anatomic and oncologic goals. Experience with keyhole approaches to this region is somewhat limited in anyone’s hands, because there simply are not that many pineal tumors in anyone’s practice to gain extensive experience with keyhole pineal surgery. However, an explication of anatomic principles of this region and some basic surgical principles of keyhole surgery are provided to further assist those interested in minimizing surgical impact during pineal surgery. Although this review, for the sake of brevity, focuses on the infratentorial-supracerebellar approach, many of these principles can be adapted to other approaches, such as the occipital transtentorial, without excessive imagination.

Keyhole surgery

The term keyhole surgery does not refer to a specific technique but to a philosophy that emphasizes using the smallest opening necessary to achieve the anatomic goals of surgery. Although it is difficult to prove that smaller craniotomies are better than larger ones, larger craniotomies expose more brain surface to the air and microscope light (ie, nonphysiologic conditions) for longer periods of time, and larger incisions are generally more prone to wound complications and pain than smaller ones. However, this does not imply that it is wise to make the opening so small that dangerous maneuvers, or lack of visualization, are part of the surgery; in some cases keyhole craniotomies might be large. Instead, it implies that the least exposure necessary is the optimal exposure.

Keyhole surgery requires some modification of traditional techniques. Most notably, the smaller hole requires more frequent alterations of the viewing angle to achieve all the necessary views. The patient should be secured to the bed in all directions to ensure safety with frequent repositioning, and the surgeon should be prepared to frequently adjust the microscope. A mouthpiece adjustment device might be helpful for this. In addition, endoscope assistance might be necessary to achieve otherwise challenging angles of visualization. Using a keyhole approach requires a degree of planning not needed with larger conventional craniotomies, because it is much harder to adjust the approach midsurgery. Image guidance is essential, and obtaining accurate registration is more important in these cases generally, because you do not always get all the angles of visualization you might in a larger craniotomy. Keyhole surgery requires patience in a way that is not always seen with larger craniotomies. Although the work required to do a smaller exposure is less, each step requires more attention to detail and a conscious effort to slow down, because minor imperfections are less tolerated in a small space, and the time needed to drain more cerebrospinal fluid and get the brain out of the way before beginning arachnoidal dissection and intradural work is longer.

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