Fig. 18.1
(a–f) MRI sequence: (a axial T1, b coronal T1, c coronal enhanced T1 and d sagittal T1) of a 40-year-old woman presenting with classical apoplexy, who suffered sudden and worsening severe headache and new bitemporal visual field loss. Scans (a–d) show a mixed density lesion in and above the pituitary fossa compressing the chiasm. Note the multilobulated lesion with narrow waist and the prefixed chiasm pushing the adenoma back over the sella. This is a difficult surgical target. Operated by transsphenoidal approach by a reasonably experienced surgeon who was unable to remove any suprasellar component, the patient failed to wake from surgery, and an early postoperative CT scan (e) shows further haemorrhage in residual tumour and extension into caudate region. Following a further emergency craniotomy, the patient is left with an established infarct on CT some days later (f) and is completely blind
18.3 Surgical Style: What Approach Should Be Used?
The majority of cases of apoplexy are only really suitable for transsphenoidal surgery and transcranial surgery should be avoided except in circumstances when the tumour is so far above the chiasm that it is unlikely to be removed by the nasal route. The brain in a patient who has suffered recent apoplexy may well behave like the swollen brain of a patient with severe subarachnoid haemorrhage, and the chance of vasospasm and its sequelae also seem to be much higher than in ‘cold’ transcranial pituitary surgery. This author’s observation of emergency craniotomy in this situation would suggest that there is significant risk of severe morbidity (blindness and epilepsy) and even mortality.
The reader will be well aware that there is something of a revolution underway with regard to how the sphenoid is approached so that with more traditional and modern methods available; there is no ‘one’ correct way. Many surgeons are now adopting endoscopic approaches rather than the well-established microscope version, which is celebrating its fiftieth anniversary in 2012. There are many different minor variations of both techniques. None is wrong; it is only important that the surgeon uses a method with which he is comfortable.
Whichever is used, the essence of the approach is the same.
18.4 Anatomy
It is helpful to study a skull. From the nostril, along the septum, through to the area between the sphenoid ostia on the front face of the vomer, then through to the front face of the pituitary fossa up to its junction with the planum sphenoidale is a straight line. The nasal cavity is narrowed bilaterally on its lateral walls by the turbinates, the middle and inferior of which have to be pushed to one side on the approach regardless of the method used. In the microscope approach, this is done by the retractor, whereas in the endoscopic approach these have to be actively compressed or even resected.
By opening the rostrum of the vomer, access is gained to the sphenoid air sinus, lined with its mucosa. It is separated into compartments by sphenoid septi, usually just one and usually near the midline, separating the sinus into left and right halves. There are many variations to the position of these septi, so study of the patient’s scans is imperative, as deviation from the midline into the carotids, which lie directly on either side of the pituitary fossa, is both dramatic and dangerous. If a very lateralised septum is mistaken for one in the midline and is removed from the carotid bulge, it is distressingly easy to damage the vessel and cause massive bleeding.
The pituitary fossa hangs in the space created by the sphenoid sinus (Fig. 18.3). In apoplexy, it is, almost by definition, harbouring a macroadenoma and therefore will usually have significantly expanded the fossa from its normal dimensions and thinned the anterior wall, to paper thin.
In the skull, seen from above, the pituitary fossa has no sides but which in life is filled in by the cavernous sinus containing both internal carotids and the cranial nerves III, IV and VI. Meckel’s cave and the trigeminal nerves lie below, although are usually far enough away not to be involved. Only a thin single layer of dura forms the cavernous sinus pituitary interface lateral wall. The cavernous sinus has interconnections over the front of the fossa, sometimes referred to as the circular sinus. It lies at the junction of the fossa with the planum. Although this can be troublesome in Cushing’s surgery and in extended suprasellar approaches, it is not usually a limiting step in apoplexy surgery.
The tumour will have extended into the suprasellar space and may well be compressing the chiasm from below. The majority of physicians will recognise chiasmal compression visual loss. Equally, it may have pushed laterally and be compressing the contents of the cavernous sinus. It is of interest that cavernous invasion is common in adenomas but virtually never causes ophthalmoplegias, except in frankly malignant tumours. However, ophthalmoplegias are common in apoplexy, as mentioned above.
The posterior wall is the continuation of the clivus leading up to the posterior clinoids and the anterior wall, as previously described, the posterior, superior wall of the sphenoid. Continuation of the dura lines the whole structure. In places this has a double layer. The diaphragm sella is almost certainly thinned and stretched upwards by the previous growth of the tumour.
18.5 Surgery (Powell 2012)
As mentioned, both microscope and endoscopic approaches are acceptable. This description will focus on the endonasal/septal push over microscopic technique, but salient points in the endoscopic approach will also be mentioned. The difference between the two is that the latter enters the sphenoid directly through the ostia and does not utilise any nasal septal dissection, although, interestingly, the bone removal employed at the vomer is rather more than in the former technique. It is essentially the direct nasal approach described by Griffith and Veerapen (1987) for the microscope in 1987. The description will not cover those who prefer to use the sublabial approach. This author believes it to be an unnecessary extra dissection with no added value.
18.5.1 Surgical Position and Equipment
The patient is anaesthetised and placed supine on the table. Head up tilt is recommended as this aids venous drainage. Those employing the ‘axilla’ position for the surgeon will twist the head to suit their line of approach. Those, as this author, who prefer the ‘head of table’ (Fig. 18.2) approach will probably drop the head back for comfort.
It is likely that the patient is already on a cortisol replacement dose, excess to normal requirements; if not, it would be prudent to give the patient at least 50 mg hydrocortisone intravenously. It is also quite possible that there are protocols already in place regarding replacement. High doses of dexamethasone are frequently given, although there is no clear evidence that these influence outcome in any beneficial way and are more likely to promote diabetes mellitus. Equally, many neurosurgical units have a protocol for operative antibiotic prophylaxis. These may be employed if wished; again, there is little evidence that in transsphenoidal surgery, this has a useful place.
Ideally, the nose has been previously prepared with a nasal decongestant such as although this can be omitted.
If there is a very significant suprasellar component to the tumour, and particularly if the suprasellar part is much greater than that in the fossa, it can be very helpful to use a lumbar drain which should be put in at this point. The drain can be used to inject saline to bring the dome of the tumour down (see below), and if a cerebrospinal fluid (CSF) leak develops, it can also be used in the postoperative period to protect the repair.
The operation requires an array of specialised equipment, special retractors, dissectors, curettes and micro rongeurs. These are outlined in Figure 18.6 and their use will be described in the text. Microscope specialised tools tend to be ‘bayoneted’ to keep the holding hand out of sight, but for endoscopic approaches, this is not strictly necessary. Both can be used in either technique.
18.5.2 Endonasal Approach
The microscope is employed from the outset. Also, the fluoroscope is extremely helpful, to check orientation on the nasal approach and at the sella. It is put in place at the initial towelling up of the patient, hidden behind the drapes (Fig. 18.2).
The incision is made on the septum in one nostril (Fig. 18.3) (this surgeon always uses the right), approximately 5 mm long, well below the columella, which has small anchoring fibres that make this otherwise easy separation more tricky. The blue-grey nasal cartilage is seen and the mucosa separated from it over about 12–15 mm, ensuring the separation at the floor. This author uses a ‘Hardy’ dissector for this (Fig. 18.6, instrument 5). Following this avascular plane down deeper into the nose using a long handheld retractor, the junction of the cartilage with the bony septum is passed, onto the bony part. Here, the experienced will find the remnants of separate bones, and it will, in the correct trajectory, be extremely thin. At this point, twisting the retractor tips swiftly clockwise can crack the septum across. The blades of the retractor are placed on either side of the remains of the septum. A check X-ray can be taken at this point.
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