International Journal of Neurooncology

: 2021  |  Volume : 4  |  Issue : 3  |  Page : 27--29

Optimally invasive skull base surgery

Basant K Misra 
 Department of Neurosurgery and Gamma Knife Radiosurgery, P D Hinduja Hospital and Medical Research Centre, Mumbai, Maharashtra, India

Correspondence Address:
Dr. Basant K Misra
Department of Neurosurgery and Gamma Knife Radiosurgery, P D Hinduja Hospital and Medical Research Centre, Mumbai - 400 016, Maharashtra

How to cite this article:
Misra BK. Optimally invasive skull base surgery.Int J Neurooncol 2021;4:27-29

How to cite this URL:
Misra BK. Optimally invasive skull base surgery. Int J Neurooncol [serial online] 2021 [cited 2022 Jun 26 ];4:27-29
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Skull Base Surgery (SBS) is a relatively recent development in neurosurgery. Though sporadic attempts at SBS were made in the 20th century and initiation of interdisciplinary co-operation was done in the 1960s, it was in the 80s that SBS became an established neurosurgical discipline. The initial enthusiasm of achieving eradication of a seemingly 'inoperable' lesion by novel skull base approaches led many neurosurgeons to employ radical surgery. The accompanying high morbidity was accepted as inevitable. Over the years, however, many started questioning this philosophy and the new millennium saw the pendulum swing to the other extreme with increasing popularity of endoscopic surgery and radiosurgery. Thus, minimally invasive neurosurgery became the fashion. However, it is important to remember that inadequate treatment through a less invasive approach is maximally invasive. Realization has now dawned that endoscopic surgery, endovascular treatment and radiosurgery cannot replace but should complement skull base surgery. A judicious use of skull base approaches, with appropriate adjuncts and radiosurgery is the best way forward in dealing with various skull base lesions. Measures preventing neurovascular damage during surgery, adequate closure to prevent cerebrospinal fluid (CSF) leaks, the bug bear of skull base surgery, and quick remedial measures to prevent and treat complications will go a long way to achieve optimal results. Our philosophy is that of Optimally Invasive Skull Base Surgery (OISBS), individualizing the approach to suit the given patient with a goal to achieve maximal result with minimal damage. Neuroendoscope, image guidance, endovascular therapy and radiosurgery are all utilized as pillars on the foundation of microsurgery. OISBS may be defined as skull base surgery which is as minimally invasive as possible to achieve maximum efficiency, because inadequate treatment through a small approach is maximally invasive and adequate treatment through avoidable large approach is undesirable. When faced with a neurosurgical problem, particularly a skull base lesion, one is often faced with various dilemmas: 1. to treat or not, 2. microsurgery, radiosurgery or endovascular therapy, 3. which surgical approach, and 4. eradication or modification.

The process of decision making is most important yet difficult and depends on the following factors:- a) environmental factors, b) patient factors, and c) pathological factors

(a) Environmental factors

Rapidly advancing technology and newer modalities of treatment often require significant infrastructure development and additional training by the neurosurgeon, not to mention the increasing financial burden on the institution to remain up to date. Intense competition amongst the institutions and the industry often results in the introduction of inadequately tested technology, commonly, without significant additional benefit. It is essential, particularly in India, a country with limited resources, to be able to deploy resources sensibly. The additional problem is the maintenance and after sales service of extremely expensive machines. Many technologies are sub-optimally utilized in India because of unacceptable downtime. One of the solutions lies in the technology development in the country of origin. Till that happens, it is a fact that the treatment offered to a given patient across many parts of India is often dictated by the available facilities and is not necessarily the most appropriate one.

(b) Patient factors

Important patient factors which affect decision making are age, comorbidity, neurologic deficit at presentation, and to a certain extent, the patient's occupation and socio-economic status. Advanced age and associated comorbidities often influence us to prefer a less invasive approach, for e.g. Gamma knife radiosurgery (GKR) for an elderly patient or a patient with multiple comorbidities having a 2.5 cm vestibular schwannoma or jugular foramen tumor. On the contrary, a more radical microsurgical approach may be the better choice for a patient with affected neurology, e.g., a patient of cavernous sinus neoplasm with ophthalmoplegia, a jugular foramen tumor with lower cranial nerve palsy, or a giant carotico-ophthalmic aneurysm with visual deficit, rather than radiosurgery and endovascular therapy.

Finally, while socioeconomic factors and occupation should ideally not influence treatment decision making, in practice, it always does. A professional singer with a jugular foramen tumor, a religious preacher, or an actor with a vestibular schwannoma, may opt for a subtotal excision/a near-total excision of the tumor, with or without adjunct Gamma knife radiodurgery, to guarantee normal function so that they can pursue their career. On the other hand, a manual labourer or an economically under-privileged person from a remote part of the country may prefer a one-time microsurgical excision of a benign tumor or microsurgical clipping of a cerebral aneurysm to achieve cure and avoid multiple long term visits for follow-up.

(c) Pathological factors

Last but probably the most critical in the decision making are the pathological factors: Where is the lesion? And, what is the lesion? A parasellar extracavernous tumor like a trigeminal schwannoma or a meningioma can and should be cured by microsurgical total excision. On the other hand, the intracavernous component of a parasellar meningioma may be left without excision and observed safely or treated by radiosurgery. The author does not prescribe primary Gamma knife radiosurgery for cavernous sinus lesions without histological verification because of the risk of misdiagnosis and inappropriate treatment, as some granulomatous lesions can mimic a meningioma. Since Yasargil's report on microsurgery of petroclival meningioma (PCM), many impressive series were published in the 90s on the microsurgical management of PCM demonstrating the possibility of total excision of this formidable tumor. The recent emphasis on the quality of life (QOL) and the fact that total excision of the tumor, while good for the tumor and yielding a great postoperative scan, may not be always best for the patient, have led many neurosurgeons to change the emphasis of total excision to tailored excision and risk reduction. The total excision rates of 70 – 80% in PCM during the 90s has now fallen to around 40% in many series. This change is a result of the evidence that (i) radiosurgery for small volume tumors results in successful long term control; and, (ii) the natural history of untreated and subtotally resected PCM is not too bad after all.

Another issue which is constantly debated is the type of surgical approach, whether a more extensive skull base approach, a conventional microsurgical approach or a minimally invasive 'key hole' approach. It is essential that the surgeon is familiar with the various approaches and uses one that is most appropriate for a particular patient. Thus, a patient-oriented and not a surgeon-oriented approach results in a happy patient. The author practices a conventional pterional approach for most suprasellar meningiomas and for most anterior circulation aneurysms. A more extensive fronto temporo orbitozygomatic (FTOZ) approach is used for dorsum sellae meningioma and high basilar top aneurysms and a minimally invasive endoscopic/endoscopic assisted endonasal approach is used for pituitary tumor, cystic craniopharyngioma, Rathke's cleft cyst and midline chordoma of clivus. Sphenopetroclival meningioma (SPCM) without posterolateral and inferior extension beyond the internal acoustic meatus (IAM) is best approached by a middle cranial fossa/petrous apex approach. An orbitozygomatic (OZ) craniotomy is added for tumors extending high up in the dorsum. SPCM with significant posterior fossa extension is best managed by a two staged anterior petrosal and retrosigmoid approach. The author has in the last decade reverted back in most cases to a retrosigmoid craniotomy and supra-para cerebellar approach than a posterior petrosal approach in such a scenario and a two-staged than a long one-stage approach. While the trend in the author's practice has been a revert back to the conventional microsurgical approach in many skull base tumors which were previously operated by the extensive skull base approach, the reverse is true in the microsurgery of an aneurysm. Unlike a large tumor, which provides space for dissection after debulking, adequate exposure can only be achieved in a giant aneurysm by a dedicated skull base approach. Such an approach is especially critical for posterior circulation aneurysms.

The nature of the lesion under treatment is as important as the location of the lesion. Ample evidence is available from natural history regarding the benign nature of some pathologies which merit a period of observation rather than upfront intervention. An intracanalicular vestibular schwannoma and a less than 5 mm unruptured aneurysm in the anterior circulation are some examples. More and more incidental lesions are being picked up today because of easy availability of neuro-imaging. The author has in many instances followed up patients with benign skull base tumors with minimal or no symptoms for many years without any worsening. An apt example is a jugular foramen tumor (schwannoma or glomus) with minimal or no symptoms especially in a middle aged or elderly patient who may not require treatment in his/her lifetime. Unfortunately, sound decision-making comes with experience and experience does not come without a price. Thus, an intelligent neurosurgeon would do well by learning from all the sources available and get a second opinion, when necessary, to reduce the pain of damaging a fellow human being.

Finally, it is important to anticipate the expected post-operative QOL. Once in a while, one comes across a patient in whom any intervention would result in significant morbidity without any realistic chance of cure. It is prudent to allow nature take its course in such a scenario, than play God!

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Conflicts of interest

There are no conflicts of interest.