Intraosseous Cellular Schwannoma in the Infraorbital Region: A Rare Case

Introduction

Schwannomas, also known as neurilemomas, are benign tumors arising from Schwann cells, which form the myelin sheath of peripheral nerves [1–4]. They occur most commonly in the limbs and along the spine, with approximately one-third of cases affecting the head and neck region [2,5]. However, involvement of the infraorbital or maxillary areas is exceedingly rare [5].

Cellular schwannoma (CS) is an uncommon histological variant, accounting for approximately 3% to 5% of all schwannomas [6,7]. It is characterized by predominantly hypercellular Antoni A areas, sparse or absent Antoni B areas, and a lack of well-formed Verocay bodies. Some cases exhibit increased mitotic activity, focal necrosis, and features suggestive of aggressive behavior, such as bone erosion [6–8]. These characteristics can lead to misinterpretation as a malignant neoplasm.

Clinically, symptoms vary depending on tumor location, often including compression, pain, or sensory disturbances [2]. On CT, CS may appear as a slightly hyperdense lesion and, in some cases demonstrate cortical bone erosion [2,9,10].

Given the overlap in clinical and radiological features with other lesions, histopathological analysis is essential for accurate diagnosis. Identifying hypercellularity, absence of Verocay bodies, and confirming benign behavior helps differentiate CS from other entities such as neurofibroma, perineural tumor infiltration, and solitary fibrous tumor. Thus, a comprehensive diagnostic approach integrating clinical, imaging, and histological data is necessary to avoid misdiagnosis and to guide appropriate management [11].

Although rare cases of infraorbital schwannomas have been reported, to our knowledge, none have described the cellular subtype. We present a case of intraosseous cellular schwannoma with maxillary expansion in the infraorbital region, which posed a considerable diagnostic challenge.

Case Report

A 31-year-old man was referred for neurosurgical evaluation due to episodic right infraorbital facial pain, described as an “electric shock” sensation radiating to the maxillary region. Over the previous year, the pain had progressed from once-weekly episodes to daily occurrences. He also reported progressive right ocular proptosis with upward displacement, resulting in vertical diplopia.

Clinical and neurological examination revealed facial asymmetry due to facial nerve dysfunction, mild upward divergent strabismus, right-sided exophthalmos, and allodynia in the right maxillary region, corresponding to the distribution of the maxillary branch (V2) of the trigeminal nerve (Figure 1A, 1B). No other neurological symptoms or relevant family history were reported.

Multislice CT (Revolution ACT, GE Healthcare, Chicago, IL, USA) of the face, using soft tissue and bone windows, demonstrated an oval, expansile, slightly hyperdense lesion measuring 4.5×2.5×3.0 cm, with irregular peripheral enhancement. The lesion involved the floor of the right orbit and the posterolateral wall of the right maxillary sinus, extending into the orbital cavity and displacing the inferior rectus muscle. Anteriorly, it was adjacent to the infraorbital foramen, and posteriorly, in proximity to the foramen rotundum (Figure 2A–2C).

The patient underwent surgical resection under general anesthesia via a right subciliary incision to expose the orbital floor, infraorbital rim, and zygoma. An extended inferior orbitotomy enabled complete visualization and excision of the lesion. Microsurgical dissection was performed to preserve the infraorbital nerve bundles. The maxillary sinus was irrigated with azithromycin (200 mg/5 mL) diluted in saline. Due to tumor expansion and local bone infiltration, significant bone loss was noted in the infraorbital area, requiring reconstruction with a 1.5-mm porous titanium mesh (Figure 3A–3D). The specimen was submitted for histopathological evaluation.

Microscopic analysis revealed a neoplasm composed of spindle-shaped, oval, and round cells with loose chromatin, prominent nuclei, eosinophilic cytoplasm, and indistinct borders. Nuclear pleomorphism and occasional hyperchromasia were observed. The neoplastic cells were arranged in sheets and bundles, sometimes exhibiting nuclear palisading and central acellular zones, compatible with Verocay bodies. Numerous foamy macrophages were identified, as well as hyalinized blood vessels and focal hemorrhage, indicating a well-vascularized lesion. No atypical mitoses or elevated mitotic index were seen (Figure 4A, 4B). Immunohistochemical analysis showed strong, diffuse positivity for S-100 protein, confirming Schwann cell origin. Ki-67 staining demonstrated low proliferative activity, with predominantly nuclear labeling (Figure 4C, 4D). These findings were consistent with a diagnosis of cellular schwannoma.

The patient was discharged on the first postoperative day, without facial pain or dysesthesia. During 3 years of follow-up, he remained asymptomatic, with only mild enophthalmos and no ophthalmologic concerns.

Discussion

This report describes a rare case of intraosseous cellular schwannoma originating from the infraorbital nerve, presenting with visual disturbances and neuropathic pain. Schwannomas in this anatomical location are uncommon, and no previous reports have documented the cellular histological subtype in this region.

To investigate the frequency of infraorbital schwannomas, a literature search was conducted in PubMed, SciELO, and LILACS databases using combinations of the terms “schwannoma,” “neurilemmoma,” “neurinoma,” “plexiform schwannomatosis,” and “infraorbital.” The search yielded 26 relevant case reports, of which 19 were accessible and published within the past 20 years (Table 1). Among these, 8 lesions were located in the maxillary region [1,2,5,10,12–15], 9 in the orbital cavity [3,4,9,11,16–20], 3 in the pterygopalatine fossa [10,21,22], and 3 were extraosseous [1,5,9]. None of the reviewed cases reported histological features compatible with the cellular variant.

Schwannomas account for approximately 1% to 8% of all head and neck tumors and show a slight female predominance [2,5,9]. In contrast, the current case occurred in a male patient and involved the inferior orbital wall and the posterolateral wall of the maxillary sinus, with extension into the orbital cavity and proximity to both the infraorbital foramen and the foramen rotundum.

According to Mora-Ríos et al [19], infraorbital schwannomas typically affect individuals aged 20 to 70 years, are often asymptomatic, and may manifest as painless, progressive proptosis. In our case, the patient’s age was within this range, but the clinical presentation was distinct – characterized by enophthalmos and vertical diplopia secondary to inferior rectus muscle displacement, along with painful electric shock-like sensations in the maxillary region.

Radiologically, the lesion demonstrated features consistent with previously reported schwannomas, including a well-circumscribed, slightly hyperdense expansile mass with occasional cortical bone erosion [2,10,23]. In cellular schwannomas, such destructive growth patterns are more frequent [7]. In the present case, CT imaging revealed disruption of the orbital floor, erosion of the posterior maxillary sinus wall, and invasion of adjacent ethmoid sinuses, supporting the diagnosis of the cellular subtype.

Histopathologically, our findings were consistent with the cellular variant of schwannoma. Costa et al. [7] described this pattern as composed of tightly packed spindle cells arranged in fascicles, often displaying a storiform architecture, with predominance of Antoni A areas and absence or scarcity of Antoni B areas. Verocay bodies are typically absent, and mitotic activity can range from <1 to 12 per 10 high-power fields. Abe et al [24] and Rodriguez et al [25] emphasized that despite increased cellularity, these tumors generally have low proliferative potential. Immunohistochemistry usually reveals strong diffuse positivity for S-100 protein and low Ki-67 indices. The histological profile observed in the present case matched these descriptions, including absence of well-formed Verocay bodies, predominance of hypercellular Antoni A areas, and low mitotic activity. Strong diffuse S-100 positivity and low Ki-67 nuclear staining supported the diagnosis of cellular schwannoma.

Regarding prognosis, Casadei et al [26] argued that immunohistochemical indices such as Ki-67 are not reliable predictors of recurrence. Instead, incomplete resection and higher mitotic activity are more strongly associated with local recurrence, which ranges from 5% to 40% for cellular schwannomas – higher than for conventional types. Tumors in deep anatomical sites may be less accessible for complete excision, increasing the risk of recurrence. Given their benign behavior, accurate diagnosis is crucial to avoid overtreatment, such as unnecessary nerve sacrifice or adjuvant therapy, and to preserve function [27]. In our case, genetic testing was not performed at the time of diagnosis due to the benign clinical and histopathological presentation, as well as the absence of any relevant family history. A conservative surgical approach was adopted, preserving the infraorbital nerve. The patient has remained asymptomatic during 3 years of follow-up, with no signs of recurrence.

Conclusions

The intraosseous localization of a cellular schwannoma in the infraorbital region is a diagnostic challenge, particularly due to the absence of classic histological features such as Verocay bodies. This case contributes to the limited literature on this tumor subtype and underscores the importance of considering schwannoma in the differential diagnosis of infraorbital and maxillary lesions. Careful histopathological and immunohistochemical analysis is essential for accurate diagnosis and to guide appropriate, function-preserving treatment strategies.