Microvascular decompression of the trigeminal nerve is a neurosurgical operation in which a blood vessel compressing the trigeminal nerve is mobilised; and a Teflon sponge inserted between the two: decompressing the nerve, and alleviating neuralgia [6, 7]. A few neurosurgical practices now advocate the use of fibrin glue to maintain the Teflon sponge’s position [9]. The technique is not widely practiced, owing to the belief that adequate Teflon sponge adhesion is generally achieved due to the nature of Teflon fibres [9]. Increasing evidence in the literature suggests fibrin glue successfully prevents Teflon sponge migration and subsequent granuloma formation, a known cause of recurrent trigeminal neuralgia and hemi-facial spasm [8].
Review of initial procedure
A draining vein was found to be splitting the sensory division of the trigeminal nerve in two. It was dissected clear off the nerve. Additionally, an arterial vascular loop was found adhering to the trigeminal nerve, stuck with extensive arachnoid adhesions. This was also dissected, and a Teflon sponge was inserted around the vein and arterial loop, decompressing the nerve. TisseelTM fibrin glue drops were used to keep the Teflon sponge in place. The 7th and 8th nerve complex were noted to be clear, and standard closure was performed.
MRI FIESTA sequencing of the brain during the current presentation revealed the absence of a Teflon sponge near the trigeminal nerve with granulomatous appearances close to the 7th/8th nerve complex. This was suggestive of a dislodged Teflon sponge.
Fig. 2. Axial MRI brain scan of patient at level of internal auditory meatus (IAM)
Fig. 2a. Right IAM prior to primary procedure
Fig. 2b. Right IAM following primary procedure. Granulation tissue highlighted with orange arrow.
Review of re-do procedure
Significant arachnoid adhesions were seen around the trigeminal nerve. The Teflon sponge from the initial procedure was not visualised, and is likely displaced. A new vein cluster was found adjacent to the 7th/8th nerve complex. This was not explored. The arachnoid adhesions were dissected, and a new Teflon sponge was inserted between the vein and nerve complex, and TisseelTM was used. Fibrin glue was utilised in this patient for both procedures. Unfortunately, the sponge dislodged following the initial operation regardless.
In the immediate post-operative period, the patient experienced transient dysphagia-like symptoms which spontaneously resolved. She remains free of TN symptoms following the second surgery, and is currently off all medications for TN. In this context, we discuss the relevant neuroanatomy and physiology of the trigeminal nerve and facial-auditory nerve complex.
Relevant neuroanatomy of the trigeminal nerve and facial-auditory nerve complex
The facial nerve (CN VII) consists of sensory, motor, and parasympathetic nerve fibres, the latter of which originate at the superior salivatory and lacrimatory nuclei [3, 4]. Secreto-motor fibres originating at salivatory nuclei supply the sublingual and submandibular glands which, in normal physiology, stimulate saliva production in response to the gustatory reflex [3]. Fibres originating at the lacrimatory nuclei supply the lacrimatory glands and stimulate tear production in response to sensory input from the conjunctiva and cornea, or complex emotional stimuli [5]. Each of the nuclei supplies the ipsilateral side of the face [3-5].
The trigeminal nerve consists of motor fibres stimulating the muscles of mastication and tensor tympani muscles of the ear, and sensory fibres which innervate the head and face [3]. The trigeminal nerve has sympathetic innervation in its first two divisions; and parasympathetic innervation in the third [6]. The neuro-vascular conflict culprit of trigeminal neuralgia at the dorsal root entry zone (DREZ) is usually caused by one of the following vascular structures: the superior cerebellar artery, anterior inferior cerebellar artery, and the trigeminal and superior petrosal veins [6-8]. It is understood that compression of the sensory division of the trigeminal nerve by one of these vessels gives rise to the classical symptoms of TN [7, 8].
Pathogenesis of CTS
The most widely accepted theory behind the pathogenesis of crocodile tear syndrome attributes the condition to misdirected regeneration of gustatory fibres destined from the facial nerve to the salivary glands, to the lacrimal glands of the ipsilateral eye. As a consequence, the stimulation of the gustatory reflex stimulates lacrimation [2]. The aetiology of acquired CTS is usually associated with facial nerve paralysis secondary to trauma or an idiopathic Bell’s palsy [1, 2]. Figure 3 describes the pathway.
Fig. 3. Schematic diagram of pathogenesis of CTS
Hypothesised aetio-pathogenesis in the case
Suggested Aetio-pathogenesis
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- Surgical manipulation.
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- Arachnoid granulations
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- Dislodged Teflon sponge
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- Vascular origin (new venous cluster noted during re-do MVD)
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- Idiopathic
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Table 1. Suggested aetio-pathogenesis in discussed case
In Table 1, we summarise the possible contributing factors for this case of CTS following MVD of the trigeminal nerve. Although the patient had no other manifestations of facial nerve trauma, surgical intervention in the skull base and ensuing granuloma formation on the 7th/8th nerve complex may have stimulated misdirected regeneration of facial nerve gustatory fibres to the patient’s right lacrimal gland. Iatrogenic CTS following CN VIII surgery has also been reported, a structure also in close proximity to both the facial and trigeminal nerves [3, 4, 10]. It is possible that this patient’s CTS could be secondary to surgical intervention.
In our case, the patient had symptoms of facial and auditory nerve involvement post MVD in the form of sensorineural hearing loss and CTS. Sensorineural hearing loss is a well recognised complication in microvascular decompression of the trigeminal and facial nerve, and occurs in up to 5-8% of patients undergoing MVD [12]. We therefore suggest an inflammatory reaction of the 7th/8th nerve complex due to a dislodged Teflon sponge is a possible pathogenesis.