Fig. 13.1
(a) TN cases. (b) HFS cases. The percentages of patients judged by the new scoring system, documented using both cure rate and surgical complication rate. Total evaluation rate (T = E + C) is shown as T-0 to T-3 (Reprint with permission from Kondo et al. (2012))
13.3 Prevention of Complications and Postoperative Management
13.3.1 Postoperative Cerebellar Edema
Postoperative cerebellar edema, which is commonly induced by either inappropriate retraction of the cerebellum or intraoperative traumatization of superior petrosal veins, is the most severe and potentially fatal surgical complication in MVD. Cerebrospinal fluid (CSF) should be suctioned as much as possible by full opening of cerebellar cisterns. Cerebellar retraction should be as gentle as possible, and duration of every each retraction time should preferably be limited less than 5 min. A suction tube is preferably used intermittently instead of retractors to avoid overly strong retraction. To prevent accidental laceration of petrosal veins, the arachnoid membranes covering the veins should be cut meticulously to allow vessels movable, and the outlet (draining site) of veins to the major sinus should be reinforced using fibrin glue.
Once acute postoperative cerebellar edema is encountered, its therapy and management should be urgent and appropriate. Either ventricular drainage or urgent posterior fossa decompression surgery is needed for severe cerebellar edema.
13.3.2 Postoperative Dysfunctions of Cranial Nerves
Cranial nerve dysfunction that is not rarely seen postoperatively is cochlear and/or vestibular dysfunction. During MVD, the direction of traction should be perpendicular to the axis of the acoustic nerve. Monitoring of auditory brainstem response (ABR) is inevitable. When judging the data of ABR, clinicians should keep in mind that warning sign of adverse changes of ABR during surgery is a >1 ms delay of the latency of the 5th wave and 40 % reduction of amplitude at most.
To prevent postoperative facial nerve hypofunction, care should be taken when handling an offending artery, mostly anterior inferior cerebellar artery, with small perforators. Since hypofunction of abducent nerve can be caused particularly when handling the vertebrobasilar artery (VBA), care should be taken not to compromise the nerve by too much amount of prosthesis when the VBA is replaced. In terms of lower cranial nerve hypofunction, as these nerves are also vulnerable, impairment is mostly caused by excessive manipulation of the nerves or heat by a bipolar coagulator during the procedure. A bipolar coagulator should be carefully used near the nerves by covering the nerves with a wet cottonoid for protection.
13.3.3 Postoperative Liquorrhea
Postoperative liquorrhea is also a very troublesome complication after MVD. For prevention, watertight closure of dura mater should be achieved using fascia or muscle piece, if necessary. The opening of the mastoid air cell can be packed and closed as tight as possible with the use of bone wax together with a section of muscle piece, bone dusts, and fibrin glue. If the opening of bony defect is ignored during procedure, postoperative CSF leak is inevitable, and its repair will be much more troublesome after surgery.
13.4 Discussion
In experienced hands, MVD for TN and HFS offers the highest likelihood of long-term successful cure of cranial nerve dysfunction symptoms along with low rates of morbidity and recurrence (Barker et al. 1966; Kalkanis et al. 2003). The objective of the present analysis of overall surgical results is to set quality criteria and standards for outcome reports following MVD to identify and assess the surgical results appropriately. The same criteria obtained from standardized method should be used to compare each data of treatment results from MVD at each neurosurgical institute (Kondo et al. 2012). And also surgeons should well realize and study the various methods how to lessen surgical complications, together with postoperative management of MVD (Taha and Tew 1966).
Little et al. (2008) described the pain response and quality of life in patients with TN treated using gamma knife surgery by assessing outcomes using the Barrow Neurological Institute (BNI) Pain Intensity Score and Brief Score Inventory. With that score, post-gamma knife treatment status was clearly analyzed and documented from score I (no pain) to V (no relief). Rogers et al. (2000) assessed not only the efficacy of gamma knife radiosurgery for TN but also complications. They presented a BNI pain scoring system and BNI facial numbness score, which was classified after treatment into four scores. Henson et al. (2005) also described treatment results such as pain response, pain recurrence, and sensory neuropathy after both glycerol rhizotomy and gamma knife treatment for TN. Although they evaluated rates of pain relief or complications, they did not combine both rates to judge overall results. Accurate diagnosis of chronic pain is, however, crucial for determining the efficacy of surgical therapy, as measurement of such subjective phenomena is difficult. Although Chen et al. recently proposed an overview of psychometric testing, such methods of evaluating surgical results for TN are too complicated to be useful in daily clinical situations (Chen and Lee 2010). Our grading system of classification is not made too detailed but is instead simplified as much as possible. On the other hand, judgment of postoperative status of HFS is relatively straight forward, as the symptoms are mainly objective in nature.
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