Trigeminal Nerve Schwannoma: A Rare Case of Multisymptomatic Cranial Nerve Involvement

Abstract

Schwannomas (SCs) are benign tumors composed of neoplastic Schwann cells and are relatively uncommon intracranially. Although these tumors are frequently associated with neurofibromatosis type 2 (NF2), they may also arise idiopathically, and their pathogenesis remains poorly understood. A 70-year-old Caucasian man presented with a two-month history of vertigo, gait imbalance, and decreased visual acuity in the left eye accompanied by photophobia, nausea, vomiting, and occasional headaches. On physical examination, he exhibited hyposmia, horizontal nystagmus, superior oblique palsy, decreased photoreactivity of the left pupil, hypoesthesia in the middle and lower left facial regions, and a positive Romberg sign. Non-contrast computed tomography (CT) revealed a hypodense, expansive lesion in the left mesencephalic-pontine region. Based on the radiological characteristics, the radiologist suggested ischemic injury or neoplasm as the leading diagnostic hypothesis. Magnetic resonance imaging (MRI) with contrast revealed a cystic-necrotic lesion with multiloculated characteristics in the left mesencephalic-pontine area, with significant mass effect and compression of the brainstem and adjacent ventricular pathway. The lesion was suspected to be a schwannoma, and the patient underwent surgical resection via left temporal and suboccipital craniotomy. Histopathological examination confirmed a schwannoma of the left trigeminal nerve. SCs are most commonly diagnosed in the second and third decades of life, often growing slowly and remaining asymptomatic until they reach a size sufficient to cause functional impairment. MRI is the imaging modality of choice, but histologic confirmation remains the gold standard for diagnosis. This case underscores the rarity of trigeminal nerve SCs presenting with symptoms resulting not only from the affected nerve but also from compression of adjacent structures, such as the vestibulocochlear and abducens nerves. It also highlights the importance of maintaining a high index of suspicion when diagnosing rare intracranial SCs. Advanced imaging techniques and comprehensive clinical evaluation are crucial for identifying complex neurological conditions, particularly when initial findings, such as CT results, suggest alternative diagnoses like stroke.

Keywords: gait imbalance; mesencephalic-pontine lesion; neurological examination; nystagmus; schwannoma; trigeminal nerve.

Figure 1. Brain CT scan showing a hypodense lesion with expansile characteristics in the left mesencephalic-pontine region.

CT: computed tomography.

Figure 2. Brain MRI showing an expansive lesion in the left mesencephalic-pontine area (axial view).

(a) Proton density + T2 sequence highlighting a globular shape with regular, well-defined borders, measuring approximately 32 mm (anteroposterior). (b) T1 sequence displaying cystic-necrotic/multiloculated characteristics. MRI: magnetic resonance imaging.

Figure 3. Brain MRI showing an expansive lesion in the left mesencephalic-pontine area (coronal view).

(a) Proton density + T2 sequence highlighting a globular shape with regular, well-defined borders. (b) T1 sequence displaying cystic-necrotic/multiloculated characteristics, measuring approximately 34 mm (coronal). MRI: magnetic resonance imaging.

Figure 4. Brain MRI showing an expansive lesion in the left mesencephalic-pontine area (sagittal view).

(a) T1 sequence showing compression of brainstem and adjacent ventricular pathway; (b) T1 sequence displaying cystic-necrotic/multiloculated characteristics, measuring approximately 27 mm (vertical). MRI: magnetic resonance imaging.

Figure 5. Histopathological result of the tumor.

H&E (hematoxylin and eosin stain) 50x: Transition between hypercellular areas of elongated cells arranged in parallel or interlaced bundles (Antoni A areas) and occasionally disposed in nuclear palisades with eosinophilic, anucleated areas between them, forming Verocay bodies. These regions are contrasted with less cellular areas consisting of round nuclei with poorly defined cytoplasm in a microcystic background (Antoni B areas).