Introduction

Trigeminal neuralgia (TGN), secondary to vertebrobasilar dolichoectasia, is a challenging surgical disorder.1 There are a plethora of drugs and procedures used to treat TGN but none is a panacea. Many clinicians believe that a neurovascular conflict is at the heart of the pathogenesis. Surgical management of TGN involves the physical separation of the nerve and the vascular loop leading to mechanical decompression. Microvascular decompression (MVD) remains the gold-standard treatment. The Gamma Knife radiosurgery (GKRS) is now as an established alternative treatment modality for TGN.2 3 4 The literature confirms better long-term pain control with MVD compared with GKRS. However, many of these patients now consider GKRS as the primary treatment modality when their pain gets medically refractory in view of its better safety and complication profile.1 4 This choice is also often motivated by the ability to avoid the hospitalization and recovery associated with the MVD procedure.

Very rarely (2% cases), a dolichoectatic vessel might be the reason of compression and intractable TGN.5 6 Statistically, most of these patients are hypertensive male in their sixth decade of life and with predominant left-sided compression. MVD provides satisfactory pain control (96% at 1 year, 92% at 3 years, and 86% at 10 years)6 but carries high chance of cranial neuropathy. It includes postoperative trigeminal sensory dysfunction (29–42%), diplopia (23–24%), facial paresis (7–10%), and hearing loss in 4 to 13% patients. The complications may be permanent in 11% cases.5 6 7 Surgery is technically difficult too, as the vessels are firm and difficult to decompress (Fig. 1A). Occasionally, it becomes impossible to insert a Teflon between the vessel and the nerve (Fig. 1B), hence other techniques, such as sling procedures, have also been proposed.8 9 Seldom, we encounter patients who refuse invasive surgical interventions or want to keep it a secondary procedure, if the primary radiosurgery fails. When secondary to dolichoectasia, the results of GKRS are not as encouraging as for typical TGN.6 10 In this article, authors discuss their experience with GKRS for this cohort of patients and evaluates the current role and indications.

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Fig. 1 (A) Dolichoectatic vessel compressing the thinned out trigeminal nerve; (B) dolichoectatic vertebrobasilar complex and enlarged vein compressing the cisternal and root entry zone of trigeminal nerve (arrow suggestive of thinned out right trigeminal nerve). BA, basilar artery.

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Fig. 1 (A) Dolichoectatic vessel compressing the thinned out trigeminal nerve; (B) dolichoectatic vertebrobasilar complex and enlarged vein compressing the cisternal and root entry zone of trigeminal nerve (arrow suggestive of thinned out right trigeminal nerve). BA, basilar artery.

Methodology

Authors described their experience in managing three patients of TGN secondary to dolichoectatic vertebrobasilar complex with primary GKRS. All patients were medically refractory and refused MVD (Table 1). No patient underwent any prior invasive intervention before GKRS. All patients were initially evaluated on clinicoradiological parameters, and the pain was prospectively evaluated on the Barrow Neurological Institute (BNI) grading3 (Fig. 2). The radiological parameters involved T1, T2, contrast, and constructive interference in steady-state sequences of magnetic resonance imaging (MRI) at 1-mm nonoverlapping continuous imaging. The trigeminal nerve was identified on all the three axes, that is, axial, coronal, and sagittal planes. The distal cisternal component of trigeminal nerve was targeted with a 4-mm single shot (Fig. 3). The prescription dose was 90 Gray at 100% isodose. The plan was unanimously approved by a neurosurgeon, radiation oncologist, and medical physicist. The clinical parameters at follow-up (3 months, 6 months, and 1 year) were pain control on the BNI grading and sensory complaints in the form of hypoesthesia and numbness. We also evaluated the degree of pain relief, latency interval for pain relief, continued requirement for medication, need for further surgical procedures, development of any new symptoms or signs, and need for and response to additional surgical procedures.

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Fig. 2 The algorithm to manage patients with intractable trigeminal neuralgia secondary to dolichoectatic vessels. BNI, Barrow Neurological Institute grading; GKRS, Gamma Knife radiosurgery; MRA, magnetic resonance angiography; MRI, magnetic resonance imaging; MVD, microvascular decompression.

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Fig. 2 The algorithm to manage patients with intractable trigeminal neuralgia secondary to dolichoectatic vessels. BNI, Barrow Neurological Institute grading; GKRS, Gamma Knife radiosurgery; MRA, magnetic resonance angiography; MRI, magnetic resonance imaging; MVD, microvascular decompression.

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Fig. 3 (A) The dolichoectatic vessel on the left side of the brain stem; (B) the radio surgical targeting of distal cisternal component of trigeminal nerve (patient A); (C) Right sided dolichoectatic vessel (arrowhead, patient B); and (D) radiosurgical targeting of the distorted right trigeminal nerve (patient B).

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Fig. 3 (A) The dolichoectatic vessel on the left side of the brain stem; (B) the radio surgical targeting of distal cisternal component of trigeminal nerve (patient A); (C) Right sided dolichoectatic vessel (arrowhead, patient B); and (D) radiosurgical targeting of the distorted right trigeminal nerve (patient B).

Results

All three patients were male of 44, 52, and 70 years, respectively, with BNI V at presentation. The follow-up period is 13, 18, and 12 moths, respectively. All patients reported satisfactory pain control at 3 months follow up (BNI III) but suffered recurrent pain at 6 months interval. All three patients developed some hypoesthesia which was non bothersome and improved by 6 months follow up. One patient received redo GKRS after 11 months of the primary GKRS and enjoyed few more months of pain relief with later failure. This patient later needed MVD and is now pain free with no hemifacial spasm at present. Intraoperatively, the arachnoid was thickened than usual and the nerve was thinned out (Fig. 1A). In view of the vessel tortuosity and increased turgor (Fig. 1B), one needs to insert more amount of Teflon than usual to avoid the recurrence of the disease. Remaining two patients are on added medication (Table 2).

Discussion

A dolichoectasia is classically defined as a vessel diameter of at least 4.5 mm.11 This leads to compression and/or distortion of ipsilateral trigeminal nerve or brain stem. A dolichoectatic vertebrobasilar complex poses unique challenge when presents with cranial neuropathy. The clinical presentation includes features of compression of cranial nerves, obstructive hydrocephalus, and intracranial ischemic or hemorrhagic events.12 In extreme cases, there might be features of brain-stem compression including long-tract signs. The rarity of this situation can be understood by the fact that even in the famed series of Peter Jannetta, there was not even a single case of dolichoectasia. The mechanical distortion in dolichoectasia is axiomatic warranting physical separation of vessel from the nerve. However, the MVD remains technically challenging. There are high chances of postoperative cranial neuropathy, which remains permanent in 11% of cases.6 The spectrum of the surgical management ranged from rhizolysis, GKRS, MVD, and radiofrequency ablation to foramen magnum decompression.13

Conclusion

The deterrents against radiosurgery for TGN secondary to dolichoectasia are poor pain control, longer latency period, high chances of recurrence, and need for additional procedures. An advantage of GKRS is a day-care treatment and much favorable morbidity and mortality profile, as there is negligible chance of cranial neuropathy. GKRS should only be proposed to the patients who deny surgical intervention or who are not suitable candidates for surgery. It definitely remains an alternative option in patients with extremes of age or severe comorbidities to buy some time. However, its role as a definitive treatment is questionable in this particular patient population.