Volume 1, Issue 3 , Pages 220-225, September 2006
A pediatric case of neurofibromatosis type 2 presenting as a plexiform schwannoma of the intraparotid facial nerve:
A review of the world literature on the presenting pathology
Article Outline
Summary
We report a case of a 12-year-old boy who presented with a 1-year history of left facial swelling. During surgical exploration of the parotid gland, a plexiform schwannoma of the facial nerve was discovered. Subsequently other features of neurofibromatosis type 2 (NF2) were unravelled—bilateral intracanalicular facial schwannomas, and ependymoma of the spine. We detail the course that led to achieving this extremely rare association. This is the eighth case of plexiform schwannoma associated with neurofibromatosis type 2 reported to date, the first ever to involve a cranial nerve, and the third to present in the pediatric population.
Keywords: Neurofibromatosis type 2, Plexiform schwannoma, Intraparotid, Facial nerve
Introduction
The estimated incidence of tumors originating from the intra-parotid facial nerve ranges from 0.2% to 1.5% [1]. According to the current literature, it is likely that the most experienced surgeons might not encounter them in a life-long career [2]. Prior reports indicated that standard investigations of a parotid mass (fine needle aspiration [3] and imaging techniques [4], [5]) were not of value in predicting the diagnosis. Furthermore, in the absence of facial nerve weakness, there is no basis for suspecting an involvement of the nerve in the process [4]. Uniformly these tumors are diagnosed incidentally during exploration of a parotid mass [2]. Whereas the intraoperative gross appearance of a facial schwannoma does not differ significantly from that of other benign tumors [3], surgeons should suspect it if they encounter unusual difficulty in locating the trunk using standard landmarks [6], [7].
In this paper, we describe a 12-year-old boy whose left facial swelling proved to be a plexiform schwannoma (PS) of the facial nerve. Surprisingly it was the first of multiple features of neurofibromatosis type 2 (NF2) to present in this patient. This is the third pediatric case involving a PS in association with NF2, and the first to present with a cranial nerve involvement. We will discuss developments in the diagnosis and management of this unique presentation of NF2.
Case report
A 12-year-old boy was referred to a peripheral Hand clinic for claw hand deformity. The patient related the problem to a fall that he sustained when he was 4 years of age. Nerve conduction studies and diagnostic investigations produced no appreciable cause of the ulnar nerve motor branch palsy. He also had a swelling to the left parotid region of 1-year duration for which a computerized tomography (CT) scan of the neck was requested. This suggested a solid mass within the deep portion of the left parotid, with numerous small swellings, presumed to be associated lymph nodes. At the same time, routine radial and chest X-ray indicated a diagnosis of moderate dextroscoliosis centered in the mid-thoracic spine.
Nearly a year later he was referred to our clinic to assess the facial swelling. It occupied the left parotid region, was diffuse externally, and palpable and visible intra-orally (Fig. 1A and B). Another swelling was discretely palpable externally along the mandible in the region of the peri-facial lymph node. He reported occasional tenderness and fluctuation in size, but no effect on facial movement. There were no other otolaryngological symptoms and no relevant family history, trauma or surgical history. The CT scan was repeated, and followed by magnetic resonance imaging (MRI). The lesion was better appreciated on the latter (Fig. 2A), and appeared elongated in an anterior–posterior (AP) fashion, involving the parotid gland, lying lateral to the left masseter muscle. There were cystic components on the anterior and posterior aspects of the lesion. The lesion enhanced with gadolinium, except for the cystic components. The radiologist's differential diagnosis included hemangioma, sarcoma, lymphangioma, or lymphoma, and a biopsy was suggested. A left-sided parotidectomy was scheduled.
Fig. 1.
(A) External aspect of mass. (B) Intra-oral aspect of mass. (C) Resected facial nerve and tumor.
Fig. 2.
(A) An axial gadolinium-enhanced T1 weighted fat-saturated image. *, plexiform schwannoma of the facial nerve; M, masseter muscle; P, Parotid gland; V, posterior facial vein. (B) An axial gadolinium-enhanced T1 weighted image of the interior auditory canals. The arrows point to bilateral vestibular schwannomas. (C) A sagittal gadolinium-enhanced T1 weighted image of the thoracic spine. *, intramedullary ependymoma, S, syrinx.
At surgery no distinct trunk of the facial nerve could be identified using the antegrade dissection (tragal pointer and posterior belly of digastric muscle) and no tissue was producing contractions of facial musculature on stimulation electrically. Eventually, retrograde identification was resorted to, along what appeared to be a string of enlarged lymph nodes overlying the cervical branch of the facial nerve. It transpired that these were nodular enlargements of the branch itself. This led into the palpable tumour, which was engulfing the actual trunk of the facial nerve. This nerve sheath tumor also extended into the bony facial canal and the mastoid, with expansion of the bone around it. A sample was submitted for frozen section, and exhibited features of a nerve sheath tumor. Subsequently, transmastoid facial nerve decompression and resection were performed (Fig. 1C). The right sural nerve and the great auricular nerve were both harvested (30 and 8.5
cm harvested, respectively), and a cable graft was performed to bridge the facial trunk with all the branches of the face, with exclusion of the cervical and frontal nerves. For temporary static rehabilitation, a 1.2g gold weight was inserted into the left upper eyelid and a facial Gore-Tex sling was fashioned to the oral commissure on the same side.
Four specimens were submitted for definitive pathologic evaluation. A multinodular appearance was evident on macroscopic examination (Fig. 3A). The largest specimen consisted of a dominant nodule with several smaller nodules variably extending as nodular protuberances from the larger nodule. Histologically, the lesions consisted of cells with elongated and tapered nuclei, randomly arrayed in hypocellular and hypercellular arrangements, fascicles and vague storiform arrays. There was conspicuous nuclear palisading with occasional Verocay body formation (Fig. 3B). Some of the nodules were encapsulated, while others were intraneural. Neither necrosis nor atypical mitoses were seen. The lesional cells were strongly positive for S-100 (Fig. 3C). The findings were consistent with a plexiform schwannoma.
Fig. 3.
(A) Whole mount of one portion of the patient's tumor demonstrating the nodular architecture. (B) Representative cellular portion of tumor, demonstrating conspicuous nuclear palisading (H & E, 10×). (C) Immunohistochemical staining for S-100 protein (20×). Note the diffuse and strong positivity.
A consultation with pediatric neurology and neurosurgery was initiated. On reviewing the MRI scans, bilateral vestibular schwannomas were present and confirmed a diagnosis of NF2 (Fig. 2B). Another MRI scan of the brain and spine was performed. The scan showed small enhancing masses within the internal auditory canal on both sides, measuring 9mm and 1.1cm in greatest dimension, consistent with schwannomas. The spine examination showed severe scoliosis, with marked thickening in diameter from C5 down to T7. A large ependymoma measuring 3.4cm in length occupied the full diameter of the enlarged spinal cord, immediately posterior to T3 and T4. A large syrinx extended from it, up to the level of C6, and narrowed irregularly to the level of C1 (Fig. 2C). Multiple enhancing nodules were found arranged around the lower medulla oblongata and upper spinal cord at the C1/foramen magnum region, as well as around the conus, cauda equina, and extending throughout the lumbosacral region, all probable schwannomas.
Ten weeks after the patient's first surgery, a multiple level thoracic laminectomy was performed for resection of the intramedullary spinal cord tumor. The histological report was consistent with an intramedullary ependymoma given the history of NF2.
One year post-operatively, the patient has good tone to the left face, with some new muscle movement around the eye and lateral temporal area. Facial reanimation procedures will be considered to restore any remaining deficits if no further development is seen.
Discussion
An English literature search of indexed articles for the period of 1966–2005 was conducted using the search phrases “plexiform schwannoma”, “neurofibromatosis type 2”, and “plexiform schwannoma AND neurofibromatosis type 2” in PubMed. The search resulted in 984 hits: 44 were deemed relevant to our case, out of which 20 articles were used. Most plexiform tumors of peripheral nerve sheath are neurofibromas, usually associated with von Recklinghausen's neurofibromatosis (NF1), and carry a significant risk of undergoing malignant change [8]. Since Masson's original description in 1956, a rare plexiform variant of benign schwannoma has been recognized as a multinodular nerve sheath tumor with a collagenous capsule, commonly located either in the dermis or subcutaneous tissue [9], [10]. It is not difficult to distinguish PS from plexiform neurofibroma histologically, as PS consists mainly of cellular Antoni A-type tissue represented by cells with small spindled or wavy nuclei with eosinophilic fibrillary cytoplasm, arrayed in cellular fascicles or bundles, often with nuclear palisading [8], [9], [11], [12]. In contrast to neurofibromas, the cells are diffusely and generally strongly positive for S-100 protein, and the lesional capsule composed of perineural cells is positive for epithelial membrane antigen (EMA) [11], [13]. Typically, the tumor occurs as a slowly growing, asymptomatic, solitary nodule in the head and neck, trunk, or other extremities [14], although other superficial and deep sites including the vulva and parotid gland have also been reported [11], [12]. The tumor is rarely painful or tender and may be multifocal [9].
NF2 is a very rare, highly penetrant autosomal dominant disorder resulting from the inheritance of a mutation in the Merlin (or Schwannomin) gene on chromosome 22, with an incidence of about 1:50,000[15]. The diagnostic criterion for NF2 requires the diagnosis of bilateral vestibular schwannomas, or two of the following together: a unilateral vestibular schwannoma; multiple meningiomas; a first-degree relative with NF2; or two of: meningioma, schwannoma, glioma, neurofibroma, or posterior subscapular opacities [16]. Genetic testing for known mutations in the NF2 gene is available at some medical centers; however, approximately 50% of cases do not involve a family history of NF2 and represent new germ line mutations that are more difficult to detect [15], [17].
Previous studies of NF2 in the pediatric population have shown that while NF2 is classically thought of as an adult disease, almost 20% of NF2 sufferers present in childhood. Furthermore, these patients are likely to have a more severe disease course with poorer outcomes [17], [18]. The pattern of presentation in children is variable, and quite different from adult onset type. While hearing loss or tinnitus is the most common presenting symptom in adult patients, less than half of pediatric patients presented with these features [17], [18], and more do so with other cranial nerve dysfunction (facial paralysis, nystagmus, swallowing impairment, etc.).
The majority of peripheral nerve sheath tumors are neurofibromas, which are more commonly pathognomonic for NF1 than NF2 [19]. While PS is usually reported as isolated cases [13], there are occasionally cases also reported in association with NF1 [8], [9], [13], [20]. Conversely, only seven cases of multiple PS associated with NF2 have been reported in the English literature to date [10], [13], [14], [19]. Our patient is the eighth case to be reported, and also the first NF2 to present with a PS of a cranial nerve (Table 1) and with none of the common symptoms of facial nerve schwannoma (hearing loss, tinnitus, or facial paralysis).
Table 1. Case reports of plexiform schwannoma (PS) associated with NF2
| Author and year | Age | Gender | Location of PS | Cranial vs. cutaneous | Family Hx of NF2 | Notes |
|---|---|---|---|---|---|---|
| Val-Bernal et al. (1995) [14] | 19 | F | Preauricular | Cutaneous | Unknown | |
| Reith et al. (1996) [10] | 16 | M | Nose, temple, forehead, pre- and post- auricular regions | Cutaneous | No | Scoliosis |
| Ishida et al. (1998) [13] | 24 | F | Upper lip, forearm, abdomen, foot | Cutaneous | No | |
| Ishida et al. (1998) [13] | 28 | M | Generalized | Cutaneous | Yes | |
| Ishida et al. (1998) [13] | 20 | M | Scalp, upper eyelid | Cutaneous | No | |
| Ishida et al. (1998) [13] | 18 | M | Abdomen | Cutaneous | No | |
| Lim et al. (2004) [19] | 10 | M | Postauricular area, hand dorsum, frontal scalp | Cutaneous | No | |
| Current case (2005) | 12 | M | Left facial nerve | Cranial | No | Scoliosis |
The rarity of the pathology and unusual presentation contributed to the relatively late diagnosis. Had the diagnosis of NF2 been clinched by the detection of the bilateral intracanalicular schwannomas of the vestibular nerves, or suspected by diagnosing the syrinx that manifested as a claw hand deformity, relating it to the facial mass would have been difficult.
Caughey et al. [2] have alluded to the difficulties of pre- and intraoperative diagnosis of intra-parotid facial nerve schwannomas [2]. We certainly encountered the problem of locating the trunk, and could only identify it using the retrograde technique. On stimulating the neural tissue, no muscle activity was demonstrated. This contrasts to the said authors’ experience. Interestingly, they indicated that if stimulation of the mass produced contractions, this should establish the diagnosis and lead to the cascade of steps they recommend as a working algorithm. Having identified the trunk, the decision to biopsy the lesion (and the nerve by proxy) should be affected by pre-operative function, the age of the patient, the patient's or the family's choice and the overall diagnosis as function will likely be diminished afterwards. That window of opportunity was missed in our case, and it is difficult to comment on how this could change the outlook or quality of life taking into consideration the expected unfavorable prognosis.
Conclusion
We have encountered two difficult clinical situations, presenting as a single disease entity in an unlikely age group. The local facial mass originating from the facial nerve is a situation that many surgeons will not see in an entire career. Whereas, its pathological nature (PS) was not a surprise for this location, it has never been associated with NF2 previously. The available information could not have helped the management team piece together the diagnosis, develop a plan of action, or counsel the family regarding the prognosis in any better way.
References
- . Multicentricity of intraparotid facial nerve schwannomas. Ann. Otol. Rhinol. Laryngol. 2001;110:871–874
- . Intraparotid facial nerve schwannoma: Diagnosis and management. Otolaryngol. Head Neck Surg. 2004;130:586–592
- . Tumors of the nervous system. In: Barnes L editors. Surgical Pathology of the Head and Neck. 1st ed.. New York: Marcel Dekker Inc.; 1985;p. 553–663
- . Facial nerve schwannomas: CT and MR findings. Yonsei Med. J. 1998;39:148–153
- . Magnetic resonance imaging and intraoperative frozen sections in intratemporal facial schwannomas. Am. J. Otol. 1995;16:68–74
- . The changing faces of a parotid mass. J. Laryngol. Otol. 1999;113:938–941
- . Benign intraparotid schwannomas. Laryngoscope. 1972;82:199–203
- . Benign plexiform (multinodular) schwannoma: A rare tumour unassociated with neurofibromatosis. Histopathology. 1986;10:971–980
- . Plexiform schwannoma. Am. J. Dermatopathol. 1994;16:288–293
- . Multiple cutaneous plexiform schwannomas. Report of a case and review of the literature with particular reference to the association with types 1 and 2 neurofibromatosis and schwannomatosis. Arch. Pathol. Lab. Med. 1996;120:399–401
- . Congenital and childhood plexiform (multinodular) cellular schwannoma: a troublesome mimic of malignant peripheral nerve sheath tumor. Am. J. Surg. Pathol. 2003;27:1321–1329
- . Deep-seated plexiform schwannoma: a pathologic study of 16 cases and comparative analysis with the superficial variety. Am. J. Surg. Pathol. 2005;29:1042–1048
- . Phenotypic diversity of neurofibromatosis 2: association with plexiform schwannoma. Histopathology. 1998;32:264–270
- . Cutaneous plexiform schwannoma associated with neurofibromatosis type 2. Cancer. 1995;76:1181–1186
- . Neurofibromatosis Type 2. In: Lalwani A editors. Current Diagnosis and Treatment in Otolaryngology—Head and Neck Surgery. 1st ed.. New York: McGraw-Hill Medical; 2004;p. 833–836
- . A clinical study of type 2 neurofibromatosis. Q. J. Med. 1992;84:603–618
- . Paediatric presentation of type 2 neurofibromatosis. Arch. Dis. Child. 1999;81:496–499
- . Neurofibromatosis 2 in the pediatric population. J. Child Neurol. 2003;18:718–724
- . Neurofibromatosis type 2 with multiple plexiform schwannomas. Int. J. Dermatol. 2004;43:336–340
- . Plexiform neurilemmoma: A clinicopathological and immunohistochemical analysis of 23 tumours from 20 patients. Virchows Arch. A Pathol. Anat. Histopathol. 1987;411:305–309
PII: S1871-4048(06)00064-5
doi:10.1016/j.pedex.2006.06.001
© 2006 Elsevier Ireland Ltd. All rights reserved.
Volume 1, Issue 3 , Pages 220-225, September 2006
