gms | German Medical Science

In surgery for vestibular schwannoma we all try to obtain total removal of the tumour while maintaining a fully functioning facial nerve and socially functioning hearing.

It is however, not always possible to remove the whole of the vestibular schwannoma. In these cases, it then may be best to do a resection which is less than total in order to preserve function.

The question is, does leaving a remnant of tumour behind lead to a greater risk of recurrent disease?

Few papers have looked at recurrence rates after less than total resection. Those that do, only have small numbers of patients in them, so it is difficult to establish exactly what the true recurrence rate really is.

One large study by Samii et al. [Ref. 1] which looked at one thousand resections quoted a 1.4% recurrence rate after total resection.

Unfortunately at present, we can not predict which tumours are more likely to re-grow.

So, if the resection is less than total, then the need for post-operative scanning becomes even more important.

Currently, there is no consensus on when post-operative scans should be performed.

In our unit the protocol varies. If the resection was total, then we scan at three years. If the patient had a less than total resection, then we scan at one and three years.

An additional problem is that MRI scanning may give results which are difficult to interpret. This is especially the case with linear enhancement, which is a common finding following surgery & does not necessarily indicate recurrent tumour.

Nodular enhancement on MRI scans is probably more suggestive of recurrence and we will discuss the significance of these two post-operative radiological findings later.

We looked at a series of 314 vestibular schwannoma resections performed at the Wessex Neurological Centre between 1991 and May 2002.

The following data was collected prospectively:

1.

Surgical approach

2.

Totality of resection

3.

Histology

4.

Result of the three year MRI scan

Only patients with histologically confirmed vestibular schwannoma and who had complete sets of data were included in the study.

This information was available for 171 out of the 314 patients.

The majority of cases (157) were carried out via a translabyrinthine approach. Fourteen of the 171 patients underwent a retrosigmoid approach.

Totality of resection was recorded as total, partial or subtotal, with “partial” being defined as a sizable piece of tumour left behind and “subtotal” as a small piece of capsule left on the facial nerve.

For the purposes of this study partial resections were excluded as we know they have residual disease.

The three year MRI result was recorded as normal, linear enhancement or nodular enhancement. In many cases, linear and nodular enhancement were minute in size and no minimum size was excluded.

The main aim of this study was to compare the three year MRI results with the totality of resection, to see if the surgeon could predict at the end of the operation which patients would be more likely to have nodular or linear enhancement on their three year scan. This may, in turn, indicate which patients were more likely to develop recurrence and possibly provide a guide to the timing or duration of follow up of these patients.

We looked at the entire group i.e. both translabyrinthine and retrosigmoid, to see if there was any correlation between sub-totality of resection and the presence of nodular enhancement on three year MRI.

Nodular enhancement was present in 6 out of 32 subtotal resections and 9 out of 135 total resections, so nodular enhancement does appear to be more frequently associated with subtotal resections.

When we compared the three year MRI with one year MRI in the patients with nodular enhancement, only one of the nodules had increased in size.

In addition, when comparing reports of nodular enhancement from different centers, it is evident that our radiologists report very tiny areas as nodular, with the majority of our nodules being 2 mm or less in diameter.

We then looked to see if there was any correlation between sub-totality of resection and linear enhancement. Again, our figures suggest that linear enhancement is more frequently associated with a sub-total resection and this therefore may also be an indicator of possible recurrence.

Another point of interest which we found, but which is not shown in the results table is that no cases of linear enhancement on one year MRI became nodular at three years.

Both groups have a greater incidence of enhancement following subtotal resection and these results are statistically significant at the 95% Confidence Interval using the Chi-square test.

Table 1 [Tab. 1]

Enhancement on post-operative imaging is seen in all resection groups. Any patient may develop recurrence, even if the primary resection was thought to be complete.

Our study of MRI findings indicates that this risk is probably greater if the resection was less than total. Serial scanning is therefore particularly important in these cases.

From the paper by Brors et al. [Ref. 2], we know that only nodules which grow progressively on serial scans can confidently be diagnosed as recurrent disease.

Our study also indicates that the presence of linear enhancement may be as important as nodular enhancement in pointing to the need for continuing MRI review.