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Synchronous orbital schwannoma and mandibular ameloblastoma: a case report

Midion Mapfumo Chidzonga1* Mahomva L 2, Blessing Zambuko3 and Welcome Muungani4

1,2,4Specialist Consultant Oral and Maxillofacial Surgeon, Department of Oral Health, University of Zimbabwe Faculty of Medicine, ZIMBABWE
3Consultant Histopathologist Private Practitioner, Lancet Clinical Laboratories, ZIMBABWE

*Corresponding author

*Midion Mapfumo Chidzonga, Professor and Specialist Consultant in Oral and Maxillofacial Surgery, Department of Oral Health, University of Zimbabwe, Faculty of Medicine and Health Sciences, Mazowe Street, Parirenyatwa Hopsial Grounds,P.O.Box A178, Avondale, HARARE, ZIMBABWE

Abstract

Introduction:

Synchronous orbital schwannoma and mandibular ameloblastoma are unknown. Ameloblastoma is a common benign non-encapsulated, slow-growing, locally invasive odontogenic tumor of epithelial origin with several histologic variants and a high recurrence rate.  Schwannomas are uncommon in the orbits, accounting for 1-2% of all orbital tumors, and are slow-growing tumors originating from the Schwann cells in the neural sheath of peripheral nerves. We are reporting a case of synchronous orbital schwannoma and mandibular ameloblastoma in a 47-year-old male.

Key words: Ameloblastoma, mandible, schwannoma, orbital schwannoma, surgical resection, nerve sheath tumor.

Case Report

Ameloblastoma is the second most common benign odontogenic tumor of epithelial origin:  slow-growing, persistent growth potential, locally invasive, destructive, with several histologic variants [1]. It occurs most commonly in the mandible (80%), in the molar/ramus region, and may cause marked thinning of cortices, and can also erode through the cortices extending into the surrounding soft tissues [2,3].  Ameloblastoma may also occur in the maxilla. The solid/multicystic type is the most common comprising 91% of all ameloblastomas [2,3]. Other histologic variants include the desmoplastic, unicystic, and extraosseous/peripheral types [2]. Radiographically they appear as well-defined, corticated, uni- or multiloculated radiolucent entities with coarse, curved septa that sometimes present with soap-bubble or honey-comb appearance [1] CT scan findings include cystic areas of low attenuation with iso-attenuating soft-tissue regions [1]. Root resorption with possible displacement is common with these lesions [1]. Benign lesions show directional root resorption secondary to pressure effects, unlike malignant and inflammatory lesions which cause non-directional root resorption [1, 2]. They have a high recurrence rate following conservative management.

Schwannoma also known as neurilemmoma, neuroma, and perineural fibroblastoma is a solitary,slow-growing, rare benign, neural tumor derived from Schwan cells [3]. Schwannomas of the head and neck account for approximately 25-45% of extracranial schwannomas . Schwannoma arises from any cranial, peripheral, or autonomic nerves that contain Schwann cells presenting in three clinical forms: localized schwannoma, in association with neurofibroma (von Recklinghausen syndrome), and schwannomatosis [2, 4]. Orbital schwannoma is rare, comprising 1-2% of all orbital tumors [3, 4].  Surgical approaches vary with tumor location, can be transcranial, facial, or endoscopic [1]. Schwannoma has been reported in the mandible [6,9].

Intraosseous schwannoma in the mandible is rare and poses diagnostic and therapeutic challenges [5-9]. Orbital ameloblastoma due to maxillary ameloblastoma invasion has been reported [6].

We are reporting a 43-year-old male with synchronous mandibular ameloblastoma and orbital schwannoma.

Case presentation

On 22 May 2023 a 43-year-old male was referred to our Oral and Maxillofacial Surgery Clinic by the Ophthalmology Clinic in our hospital. He presented with a right orbital 8 x 8 cm. mass growing slowly over the past 2 years (Figure 1). It had grown insidiously with swelling of the right eyelid and was non-pulsatile. The mass was now tender and painful. He recalls that he had an evisceration of the right orbit more than 10 years ago. His medical history indicated that he is hypertensive on amlodipine/losartan. A computed tomography scan (CT scan) of the brain done on 11 March 2023, showed a normal brain, a large soft tissue mass replacing the right globe, nerve, and extraocular muscles growing posteriorly along the optic canal and encroaching onto the right temporal lobe, and an expansile right mandibular bone lesion (possibly ameloblastoma or dentigerous cyst) (Figure 2).The paranasal sinuses were normal. The CT scan of the orbits, pre- and post-contrast showed normal left globe, extraocular muscles, and optic nerve were all within normal limits. Differentials for the orbital tumor were rhabdomyosarcoma, meningioma, schwannoma, or lymphoma, and ameloblastoma for the mandibular tumor. Intraoral examination revealed a bony hard right mandibular body tumor (Figure 1). The tumor had been growing been growing slowly over the past 22 years. The tumor also had multi-cystic areas extending from the distal of the right mandibular first molar to the mesial aspect of the left mandibular second premolar. There was buccal and lingual bone expansion covered with normal mucosa. The right mandibular premolars and molar teeth were deranged. Dark-colored cystic fluid was aspirated. An orthopantomograph showed a multiloculated radiolucent lesion (Figure 3).

Incision biopsies were done on 12/06/2023 which confirmed the orbital tumor as a schwannoma and the mandibular tumor as an ameloblastoma. The tumors were excised under the same general anesthetic procedure. The right orbital tumor was enucleated and it measured 1.2x1.0x4.0 cm. (next to the white paper (Figure 4). Figure 5 shows the tumor bed after tumor excision, with unaffected orbital bone exposed.

A submandibular approach was used for the mandibulectomy (Figure 6). Mandibulectomy was performed from the distal of tooth 35 (1.5cm. of normal bone was preserved), with disarticulation of the right mandibular temporomandibular joint. Immediate post-resection reconstruction was done using a K-wire to support the floor of the mouth to maintain the airway and the chin in a “normal” position. The patient tolerated the procedures well. Figure 4 shows the surgical specimens. Microscopic examination of the orbital tumor revealed a neoplasm composed of bland spindle cells with elongated wavy nuclei and fibrillary cytoplasm, forming short interlacing fascicles, set in a collagenous stroma with areas of myxoid degeneration. Some areas exhibited nuclear palisading. Scattered mast cells were seen in the background. There were no significant atypia and no mitoses were seen. There was no evidence of lesional necrosis or hemorrhage. These features are consistent with a benign nerve sheath tumor, schwannoma (Figure 7).

Microscopic examination of the mandibular tumor showed bone and fibroconnective tissue with a cystic/solid neoplasm, composed of anastomosing trabeculae of squamous epithelium, with peripheral nuclear palisading and central stellate reticulum (Figure 8). These features are consistent with an ameloblastoma.The postoperative view of the patient is acceptable at a 6-week review (Figure 9). The patient refused further bone graft surgery or exploration of a possible extension of the schwannoma on the temporal lobe.

Figure 1: Patient’s view at first presentation showing orbital tumor and the mandibular ameloblastoma.

Figure 3: Orthopantomograph showing multiloculated mandibular tumor.

Figure 4: Surgical specimens of the tumors.

Figure 5: Surgical bed after tumor enucleation.

Figure 6: H&E x 40. Moderately cellular soft tissue neoplasm comprising bland spindle cells with focal nuclear palisading typical of a schwannoma.

Figure 7: Submandibular approach for the ameloblastoma.

Figure 8: H&E x 100. Conventional ameloblastoma comprising irregular anastomosing trabeculae of cells with peripheral palisading, reverse polarity, and central loose stellate reticulum-like areas.

Figure 9:Patient view 6 weeks postoperatively.

Discussion

The current case report documents a synchronous mandibular ameloblastoma and orbital schwannoma in a 43-year-old patient. To our knowledge, this is the first-ever report of a synchronous mandibular ameloblastoma and orbital schwannoma. The ameloblastoma grew slowly for the past 22 years and the “recurrent” orbital schwannoma grew slowly for over 10 years. There is an association between schwannoma and neurofibromatosis type 2 (NF2) with approximately 18% occurring in patients with neurofibromatosis type 2 (NF2). Ninety percent (90%) of schwannomas are solitary and sporadic. Synchronous multiple schwannomas are characteristic of neurofibromatosis type 2 (NF2). Primary orbital schwannoma is a benign, slow-growing peripheral nerve sheath tumor affecting patients from 20 to 40 years of age [14]. Orbital schwannoma is rare and typically presents in patients between the third and sixth decades of life but can present at any age with no gender predilection [7]. Our patient is a 43-year-old male. The schwannoma in our patient could be a recurrence based on the history of evisceration of the right orbit more than 10 years ago. The histopathologic report was unavailable. Schwannoma is rare in the orbit affecting mostly sensory nerves within the orbit [13, 14]. However, schwannoma has been associated with neurofibroma, cavernous hemangioma, and glioma [15]. It is usually asymptomatic and presents with painless proptosis, diplopia, and symptoms suggestive of compressive optic neuropathy as the lesion grows [14]. Our patient presented with a slow-growing painless right orbital mass.

  1. The WHO Classification of Head and Neck Tumors classifies ameloblastoma as a benign epithelial odontogenic tumor and Schwannoma as a grade 1 benign tumor [10]. Ameloblastoma may arise from the rests of the dental lamina, enamel organ, an odontogenic cyst's epithelial lining, or the oral mucosa's basal cell layer. Synchronous ameloblastoma has been reported with other benign tumors such as calcifying odontogenic cysts, and keratocystic odontogenic tumors [1, 2, 9 13]
  2. Ameloblastoma and schwannoma are slow-growing benign tumors with almost similar clinical features. The clinical features of ameloblastoma vary from incidental findings on imaging to painless swellings and pain or rapid growth in invasive ameloblastoma, tooth displacement, and root resorption. Orbital schwannoma presents as a painless, non-pulsatile ocular proptosis, displacement of the globe, or palpable mass in the orbit in patients between the fourth and sixth decades of life, but can present at any age. Ameloblastoma’s age of occurrence varies depending on the type of ameloblastoma: conventional type, between 40 and 50 years; unicystic type, between 20-30 years; and extraosseous/peripheral type, between 50 and 70 years. Our 43–year–old patient is in the age group affected by both tumors.

Surgical biopsy and imaging are important diagnostic tools. An orthopantomogram showed a multiloculated lesion characteristic of an ameloblastoma. CT scan is useful in demonstrating well-defined unilocular or multilocular radiolucencies and expansile lesions. CT scan has less diagnostic value for orbital schwannoma. It is, however useful for assessing bone expansion and erosion. The tumor appears as smooth, oval, spindle, and elongated shape. Magnetic resonance imaging [MRI] assists in demonstrating soft tissue and marrow extension beyond the lytic bone cavity and extension to other areas (orbit, paranasal sinuses, and cranium) for maxillary lesions. MRI for orbital schwannoma is classically hypointense (can be isointense though) on T1-weighted imaging and hyperintense on T2-weighted imaging [11]. On postgadolinium MRI schwannomas enhance, either homogenously or heterogeneously 11. On ultrasound orbital schwannoma appears as oval or lobulated masses with heterogenous middle-to-low internal reflectivity. Doppler ultrasound shows flow signals inside the tumor [11]. Our patient could not afford further MRI and ultrasound investigations.

Recurrences of ameloblastoma can occur after as long as 10-15 years post-surgery, with a recurrence of 55-90% after conservative treatment and 15-25% following a radical approach [17]. On the other hand orbital schwannoma recurrence rates are low [11]. Pre-surgical biopsy provides a histopathological definitive diagnosis that directs appropriate wide surgical excision of 1-2 cm. into the normal bone for mandibulectomy and meticulous avoidance of breaching the very thin capsule of the schwannoma. This approach would limit the possibility of recurrences. Ameloblastoma, with a recurrence rate of 55-90% after conservative treatment and 15-25% after radical surgery can recur 10-15 years after surgery [17]. This calls for long periods of follow-up of the patients. Our patient is on yearly review for possible recurrences.

Conclusion

We present the first case of synchronous mandibular ameloblastoma and rare orbital schwannoma. These benign tumors have high recurrence rates, especially if the appropriate treatment modality is not implemented.

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Journal of Clinical & Medical Case Reports, Images (JCMCRI) ISSN: 3064-8025 is a peer-reviewed journal dedicated to publishing clinical images from all sectors of medicine. The goal of this magazine is to disseminate information about new discoveries and treatments in science and medicine.

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