Myiasis and Pneumolabyrinth

Pneumolabyrinth Following Aural Myiasis

Authors: Anjali Lepcha, MS, DNB; Sunithi Elizabeth Mani, DMRD, MD; Achamma Balraj, MS, MSc; Mary Kurien, MS

Institution: Department of ENT Unit IV and Department of Radiodiagnosis,
Christian Medical College & Hospital. Vellore, Tamilnadu, India.

Corresponding Author:

Anjali Lepcha, MS, DNB
Department of ENT Unit IV,
Christian Medical College & Hospital,
Vellore 632004,Tamilnadu. India
Tel: Office: +91-416-2286075/2283154/2282898
Facsimile: +91-416-2232035/2103
Email: anjalilepcha@yahoo.com

Abstract:

This is a report of an unusually aggressive infestation of aural myiasis in a normal ear causing pneumolabyrinth; a rare sign, demonstrated radiologically on CT scan. Surgical intervention is necessary in the management of such patients along with intravenous antibiotics to avoid fatal outcome. To the best of our knowledge this is the first such case reported in medical literature.

Introduction:

Aural myiasis almost always occurs in ears that are discharging, although rarely it also infests normal ears of debilitated individuals with poor personal hygiene.¹ Commonly they can cause external canal edema with ear drum perforation, but cases of aural myiasis causing meningitis and brain infestations have been reported.² Treatment of this condition is with broad spectrum intravenous antibiotics and manual plucking of the maggots. Surgical exploration is necessary in case of complications. Pneumolabyrinth is a rare finding on high resolution CT of temporal bones and the sign is described for the presence of a perilymphatic fistula.³ This complication following aural myiasis is reported for the first time and its management discussed.

Case Report:

A 50 year old man with no prior ear history presented with right-sided otalgia, otorrhoea, hearing loss and vertigo of two to three days duration. Three days prior to the onset of symptoms he reported a fly entering his right ear, moving about and exiting after several minutes. On exam, the external auditory canal was edematous with bloody otorrhoea. Notably, several live maggots were also found in the canal and manually removed under a binocular microscope. He also had a left beating third degree nystagmus but no facial weakness. He was put on intravenous antibiotics, analgesics and vestibular sedatives.

A high resolution Computed Tomogram (CT) scan of temporal bones was done using a Philips Brilliance Multislice (6) CT scanner at 512 matrix using a slice thickness of 0.8 mm and a slice overlap of 0.4 mm at bone window (WL 350, WW 1500) and reconstructed at 1x1 mm in axial and coronal sections. There was opacification of the mastoid air cells and soft tissue in the external auditory canal and middle ear. (Figure 1 to the right). The foot plate of stapes was not visualized at the oval window. The malleus was normal. Air pockets were present within the semicircular canals and the basal turn of cochlea, vestibule and middle ear (Figure 2a, b). The lateral wall of fallopian canal was dehiscent at the horizontal portion and there was an apparent dehiscence of the lateral wall of horizontal semicircular canal.

Figure 1. HRCT axial section bone windows of the temporal bones showing external auditory canal edema and mastoid air cells opacification on the right.


Figure 2. (a) HRCT axial section of temporal bones showing ossicles (malleus and incus) and parts of vestibule with tiny locules of air in the cochlear turns and the vestibule( arrow). and (b) air in vestibule (arrowhead) and air in scala vestibule of basilar turn (arrow).

The patient underwent a right mastoidectomy, canal wall up with middle ear exploration on the third day of admission. A total of 12 maggots were removed from the mastoid antrum, middle ear and tympanic orifice of the eustachian tube (Figure 3 to the right). A large marginal perforation of the tympanic membrane was found. The mastoid antrum and middle ear was filled with edematous mucosa. The ossicles were intact and the bony facial canal was found dehiscent in the horizontal section. A perilymph leak was found at the round window which was sealed with bone dust, fat and temporalis fascia. A fascia graft was placed by underlay technique to seal the perforation. The patient was put on bed rest with head end elevation in the postoperative period for 48 hours. Antibiotics were continued for a week and his dizziness was managed with vestibular physical therapy. He improved gradually but his auditory status remained poor on that side.

Figure 3. Maggots removed at surgery from middle ear and mastoid.

Discussion:

Myiasis is a rare condition usually found in the tropics and caused by larval (maggots) infestations of flies. Many factors affect the clinical and pathological manifestations of this condition and they include the genus of fly, manner of invasion by the larvae, extent of migration, number of larvae and site of invasion. These larvae do not multiply in the host and there is no systemic spread.⁴ Aural myiasis almost always occurs in ears that are discharging and it is extremely rare for it to occur in normal ears. Normal ears can get affected in cases of debilitated and immobile individuals where personal hygiene is neglected. The larvae bury into soft tissue and cause fresh wounds by their active wriggling movements. Commonly they can cause external canal edema with ear drum perforation; other complications are perichondritis and cellulitis. Petrous infestations are rare, although aural myiasis causing meningitis and brain infestations have been reported.² Aural myiasis is treated with application of topical antibiotics and manual plucking of the maggots. This process has to be repeated several times till the ear is maggot free and may take many days. Intravenous antibiotics are indicated for deeper infestations. Instillation of ether or turpentine has been advocated in the past in aiding removal of the maggots.⁵ There is a concern of ototoxicity with these methods and should definitely be avoided when tympanic membrane perforation is suspected. Surgical exploration is advisable in case of other complications.

Idiopathic perilymphatic fistula is still a debatable subject in otology. Though electrophysiological tests help in making a diagnosis, radiological demonstration of pneumolabyrinth on HRCT of temporal bones confirms clinical suspicion.⁶ Pneumolabyrinth is a rare finding on high resolution CT of temporal bones and the sign is described for the presence of a perilymphatic fistula.³ It denotes a communication between the middle ear cleft and the inner ear through which air could enter the bony labyrinth. The sign has been described after barotrauma, temporal bone fractures, stapes surgery and cochlear inplantation. Magnetic resonance Imaging (MRI) is not recommended as both air and bone do not produce signals on MRI. Other radiographic differentials for this sign would be chronic infections of the middle ear including fungal infections. In the absence of this CT sign, the commonest diagnosis for this patient would have been a labyrinthitis following acute middle ear infection secondary to aural myiasis. The persistence of audiovestibular symptoms even without radiographic demonstration of a fistula of the inner ear would warrant surgical exploration in such a patient. Spread of infection from inner ear to the meninges via subarachnoid space can occur as a complication, hence it is important to recognize this early and intervene. Although inner ear complications are rare in aural myiasis, we recommend imaging studies followed by surgical exploration if the patient has sensorineural hearing loss and vertigo. Complete facial nerve palsy may be another indication for surgical exploration. Intravenous antibiotics should be initiated early to avoid fatal outcome.

Conclusion:

Aural myiasis though hardly uncommon in tropical countries can lead to sinister neurotological complications if the disease is regarded casually. Sudden onset of cochleovestibular symptoms in a patient with aural myiasis is suggestive of a perilymphatic fistula and inner ear penetration by the larvae. High resolution CT scan of temporal bones is a useful radiological investigation in such patients. Pneumolabyrinth is a rare sign and denotes the presence of a perilymphatic fistula. Urgent surgical exploration and repair is necessary in the management of pneumolabyrinth caused by aural myiasis.

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