Schwannomas are benign tumors of the nerve sheath that arise from Schwann cells. As such, they can occur on any nerve except for cranial nerves I and II, which lack Schwann cells. These tumors are frequently found in the head and neck region, representing 25% to 45% of cases, with vestibular schwannomas being the most prevalent. Schwannomas at the base of the skull are uncommon, comprising approximately 4% of extracranial schwannomas [1,2]. Among these, vidian nerve schwannomas are particularly rare, with only 10 cases reported globally to date [3-7]. Historically, invasive methods like the maxillary swing approach were employed to access skull base tumors [3]. However, the advent of endoscopic techniques has enabled attempts at complete resection using these less invasive approaches [4-7]. Nevertheless, based on tumor location and risk-benefit assessment, approximately 13% of patients are deemed unsuitable for total resection and instead undergo subtotal resection [2]. In this report, we present a case of conservative tumor resection via an endoscopic approach for a schwannoma arising from the left vidian canal.

A 58-year-old female patient was referred to our clinic for evaluation of an extracranial tumor, which was incidentally discovered on a magnetic resonance imaging (MRI) scan. The scan was part of a follow-up and imaging study conducted by our neurology department due to right arm weakness. The patient had underlying thrombocytosis but reported no specific symptoms other than intermittent headaches and dryness of the left eye. Computed tomography (CT) and MRI scans revealed a round mass extending into the left sphenoid sinus. Based on its anatomical location, the tumor was suspected to originate from the vidian canal (Figs. 1 and 2). However, the boundary between the foramen rotundum and the mass—near the maxillary nerve—was indistinct on imaging, and the medial bony canal had been destroyed. Rather than complete excision, we therefore opted for intracapsular resection and preservation of the neural membrane, thus avoiding postoperative damage to the maxillary nerve (Fig. 2B). Endoscopic nasal surgery was performed. During the procedure, after removing the uncinate process and performing ethmoidectomy, we initially attempted a pterygopalatine fossa (PPF) approach through the posterior wall of the maxillary sinus. However, due to the intact PPF, the presence of key structures within it, and the thin lateral wall of the left sphenoid sinus evident on CT, we revised our approach to endonasal sphenoid sinusotomy, facilitating easier reduction of the tumor volume. After identifying the natural ostium of the sphenoid sinus, we widely opened the anterior wall of the left sphenoid sinus to create a large nasoantral window, ensuring a clear surgical view. The lateral bony wall was opened with a curette to visualize the tumor sheath. The tumor, composed of yellowish tissue, was suspected to be a schwannoma, with spindle cells observed in the frozen biopsy taken intraoperatively (Fig. 3A). Using a 30° endoscope, piecemeal resection was conducted with a curved curette, a ring curette, and suction. After bleeding control was achieved, irrigation was performed to ensure no residual tissue remained (Fig. 3B). Histologic examination with hematoxylin and eosin staining revealed fusiform schwannoma cell nuclei arranged in a palisading pattern. The patient was diagnosed with schwannoma characterized by densely packed cells forming Verocay bodies (Fig. 4). She was discharged on the fourth postoperative day without major complications. Eight months after surgery, the patient was continuing outpatient follow-up. She showed no signs of tumor recurrence or postoperative complications, while reporting improvement in the symptoms of dry eye and headache (Fig. 5).

Schwannomas are benign tumors that may develop in any part of the nerves encased by Schwann cell sheaths. These tumors are well circumscribed by a membrane and exhibit clear boundaries [1]. While 25% to 45% of all schwannomas are found in the head and neck region, their occurrence at the skull base is exceedingly rare [2]. The vidian canal, situated within the skull base, is a 1-cm channel positioned 5 mm posterolateral to the sphenopalatine foramen. This canal houses the vidian nerve and artery. The vidian nerve includes the parasympathetic fibers of the greater superficial petrosal nerve and the sympathetic fibers of the deep petrosal nerve, extending from the area around the internal carotid artery [8]. The vidian nerve also serves as a major landmark in intracranial surgery. A tumor in this nerve can impinge on adjacent structures and autonomic nerves, potentially leading to facial palsy, dry eye, headache, visual disturbances, and numbness of the palate.

Benign tumors, such as hemangiomas, neurofibromas, dermoid cysts, and schwannomas, can develop within the vidian canal [9,10]. Total resection is typically recommended for these benign tumors. However, the anatomical complexity of the area can impede access, necessitating treatment via subtotal resection or radiotherapy following tissue confirmation [11].

Typically, schwannomas are initially evaluated using radiographic examination. On CT scans, schwannomas usually exhibit low attenuation, like that of muscle tissue. MRI findings often reveal low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. The degree of contrast enhancement can vary, but characteristic features include the nerve entering or exiting sign, the split fat sign, the target sign, and cystic changes in the tumor [12].

In the present case, the T1-enhanced image revealed varying degrees of contrast enhancement, indicative of the target sign, while the CT scan displayed the characteristic low attenuation typical of schwannoma. Consequently, we suspected the presence of schwannoma based on the preoperative imaging findings and planned the surgical approach accordingly.

Despite the challenging anatomy, several approaches are available for excising tumors from the vidian canal. Prior to the advent of endoscopic techniques, methods such as the Caldwell-Luc procedure, lateral rhinotomy, and the infratemporal fossa approach were utilized. However, due to the difficulty of these procedures, the anatomical complexity, and the advancement of endoscopes and navigation systems, endoscopic surgery has become the predominant method. The transsphenoidal approach is now considered a safe and effective method to access the vidian canal.

Previous research has described various treatments for this lesion. These include straightforward total resection for small tumors with intact surrounding structures, radiotherapy administered after tissue examination, and the PPF approach in cases involving invasion of the PPF by the mass. In the present case, the tumor was excised via a transsphenoidal approach with intracapsular resection. The patient expressed a strong preference for surgical removal of the tumor, which was growing within the left sphenoid sinus. However, because the mass extended into the foramen rotundum, we chose the relatively conservative method of intracapsular resection over total resection. Previous research suggests that the intracapsular approach is superior to the extracapsular technique in preserving nerve function [13]. Additionally, radiographic evaluation revealed that the boundary between the tumor and the maxillary nerve was indistinct, complicating the assessment of adhesions or invasion. Furthermore, unlike typical schwannomas, nasal schwannomas can exhibit various histopathological differences because the autonomic nerve fibers that innervate the nasal mucosa lack a perineural sheath, potentially leading to non-encapsulated schwannomas in this region [14]. Thus, we opted for a surgical strategy that minimized the risk of nerve damage and proceeded with subtotal resection.

Histopathologically, schwannomas include two distinct cellular areas. The Antoni A area is characterized by densely packed cells and the presence of Verocay corpuscles or bodies, with nuclei aligned in rows. In contrast, the Antoni B area contains sparser, irregularly arranged cells. The ratio of these areas varies between tumors [15]. In the case presented, the Antoni A and Antoni B zones were clearly distinguishable, with the former displaying nuclei neatly organized in a palisading pattern around Verocay bodies. The S-100 protein, a useful marker for schwannoma, showed strong positivity in our sample, confirming the diagnosis of schwannoma.

Schwannomas are malignant in rare cases, necessitating vigilant follow-up. We performed intracapsular resection to excise the schwannoma, carefully preserving the adjacent maxillary nerve. To date, no recurrence or postoperative complications have been observed.