Volume 2, Issue 4 , Pages 235-237, December 2007
Chronic otitis caused by heterotopic brain tissue in pterygopalatine fossa
Article Outline
Summary
Heterotopic brain tissue is a rare is congenital anomaly, it may present at any age but it is frequently in infancy. This anomaly can occur most frequently in nasal region, although rests elsewhere in the digestive tract, in facial tissue or in lungs have been reported. Heterotopic brain tissue has been defined as a mass composed of mature brain tissue, outside the cranial cavity or spinal canal. We present a 9 years old girl with history of left chronic otitis and nasal obstruction caused by heterotopic brain tissue in pterygopalatine fossa.
Keywords: Heterotopic brain tissue, Parapharyngeal space, Chronic otitis, Pterygopalatine fossa, Conductive hearing loss, Glue ear
1. Introduction
Heterotopic brain tissue (HBT) is a rare congenital anomaly that was first reported by Reid [1]. It has been defined as a mass composed of mature brain tissue, outside the cranial cavity or spinal canal [2]. Literature review showed the commonest site of incidence to be in the nose [3], other reported sites were in the nasopharynx, soft palate, face, neck, parapharyngeal space, tongue, lips and lungs [4]. Apart from the HBT itself, these patients may also have other craniofacial anomalies including cleft palate, micrognathia, glossoptosis, pectus excavatum, polydactyly, anencephaly, cardiovascular anomalies and broncho pulmonary dysplasia.
HBT may present at any age, but is frequently diagnosed during infancy. It is particularly so, when it involves superficial facial tissues such as nose, eyes or lips, allowing early clinical diagnosis. When HBT is found deep in the head and neck, it is often asymptomatic and is detected incidentally during radiological imaging for unrelated reasons. Because they often remain asymptomatic, initial treatment option is conservative. Surgical excision may be performed for symptomatic lesions such as those resulting in facial deformities or obstructing the airways. Once treated surgically, recurrence is rare [5].
2. Case report
A 9-year-old girl presented with history of left chronic otitis and nasal obstruction. Clinical examination revealed left glue ear. Audiological assessment showed a left conductive hearing loss with an air-bone gap of 35 dB and a type B tympanogram was present in left ear. Endoscopy of rhinopharynx did not reveal adenoid hypertrophy but the Eustachian tube appeared compressed externally by a mass bulging in the wall of left rhinopharynx. A computed tomography (CT) scan of the head was done which showed a low attenuation mass in the left pterygopalatine fossa. The mass was eroding greater wing of left sphenoid bone. Left mastoid and middle ear cleft were filled with effusion (Fig. 1). Magnetic resonance imaging (MRI) with gadolinium showed a mass extending along the horizontal portion of internal carotid artery. It was hyper intense on T2 weighted images and hypo intense in T1 images. The mass was not contrast enhancing. Left parapharyngeal space appeared to be occupied by this mass and was causing a bulge in the wall of left rhinopharynx (Fig. 2). Patient underwent biopsy of the mass by trans-nasal endoscopic approach. Histopathology identified the mass as HBT in pterygopalatine fossa. Successively we underwent the patient to trans-maxillary (Caldwell-Luc) endoscopic surgery for total removal the mass. We removed the posterior wall of left maxillary sinus for to discover the pterygopalatine fossa. It was occupied by an isolated soft greyish tissue that was not in continuity with the intracranial compartment but it involved the left parapharyngeal space. We eliminated the mass and obliterated the surgical cavity with surgicell.
Fig. 1.
Axial CT of head that showed a low attenuation mass in left pterygopalatine fossa. The mass eroded the great wing of left sphenoid bone. The mastoid and middle ear cleft appeared opacified by effusion.
Fig. 2.
Axial MRI scan with gadolinium showed a mass extending along the horizontal part of internal carotid artery causing a bulge in the wall of left rhinopharynx.
3. Discussion and conclusion
Heterotopic brain tissue is usually seen as a mass composed of mature brain tissue. It usually consists of neuroglial elements, but may occasionally contain elements of choroid plexus too. Majority of the times it is a solid mass but in some cases the lesion can be cystic, owing to the presence of a functional choroids plexus. Generally growth of HBT parallels the growth of normal tissue. Often, HBT is totally asymptomatic and is discovered incidentally by radiologic examination for unrelated reason. In our case however, it was causing symptoms in the form of glue ear on the same side owing to the compression on the Eustachian tube. Occasionally, HBT may cause symptoms like facial deformities, usually in patients with cystic lesions or respiratory distress when the airway is involved. Associated developmental anomalies have been reported including bifid nose, cleft lip or palate.
CT scan is useful for identifying small bone defects at the skull base whereas MRI is excellent for showing communication with the adjacent brain. On CT scans of HBT, a heterogeneous low attenuation mass with or without some areas of focal cystic formation is a common feature. MRI of HBT has signal intensity characteristics similar to brain tissue on T1 and T2 weighted images. It may be hyperintense on T2 images because of dysplastic neural tissue [6].
Many theories exist to explain the origin of these lesions among which three are most commonly accepted. The first theory suggests that HBT may be derived from an encephalocele that subsequently loses communication with the brain. It has been hypothesized that, tissue protruding through the sutures of skull base may be separated from the developing brain after closure of the sutures [7]. This theory is supported by the observation that 25% of nasal HBT lesions have a fibrous extradural connection to the central nervous system [8] an alternative theory suggests that HBT may result from separation of extra cranial embryonic neuronal tissue, independent of cranial closure [9]. Finally, a third hypothesis suggests that HBT derives from isolated rests of displaced pluripotential neuroectodermal cells that successively differentiate into mature cerebral tissue [8].
Differential diagnosis of a pterygopalatine fossa mass include perineural extension of tumour along the second division of trigeminal nerve, nerve sheath tumors, angiofibromas, hemangiomas and rarely ectopic lesions of minor salivary glands. In the present case chronic otitis was caused by HBT that compressed the Eustachian tube externally.
Treatment of these tumours depends on the symptoms it produces. If they are only an incidental finding during investigation of a different problem, no treatment is usually required. However, if they are causing any symptoms either cosmetically or due to compression of important structures, complete excision of the lesion may be advised [10]. It has been reported in previous articles that a theoretical risk of cerebrospinal fluid (CSF) leak exists during surgical excision, if the heterotopic brain tissue is in communication with the intracranial compartment. However, there have been no such reports till today [11]. Also, it has been previously quoted that heterotopic brain tissue may exhibit the characteristics of a slow growing benign tumour with a reported recurrence rate between 4% and 10% [11].
Even though it is not a common occurrence in general ENT practice to see HBT, knowledge of this rare pathology is important, in order to avoid any unnecessary surgical procedures and its co-existent complications to the patient.
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PII: S1871-4048(07)00058-5
doi:10.1016/j.pedex.2007.07.001
© 2007 Elsevier Ireland Ltd. All rights reserved.
Volume 2, Issue 4 , Pages 235-237, December 2007
