Facial numbness and pain are common presenting symptoms of trigeminal schwannoma. For patients with progressively worsening or refractory trigeminal neuralgia, cranial MRI is recommended to exclude the presence of a trigeminal schwannoma.

Trigeminal schwannomas (TS) are a relatively uncommon type of brain tumor, accounting for 1% of all intracranial tumors and 0.8% of all intracranial schwannomas. They generally arise from Schwann cells of the nerve sheath, have an insidious onset, and are slow-growing. Clinical manifestations are determined by the location of the tumor and may include dysfunction of multiple cranial nerves, encompassing ptosis, diplopia, facial numbness, facial paresthesia, facial pain, masseteric weakness, facial palsy, and hearing loss.

Classification by Anatomical Location

Trigeminal schwannomas are classified according to site of origin as follows:

• Type A: Middle cranial fossa type — incidence: 40% (domestic literature); 45% (international literature)

• Type B: Posterior cranial fossa type — incidence: 41.3% (domestic literature); 24% (international literature)

• Type C: Dumbbell type (straddling the middle and posterior cranial fossae) — incidence: 10.7% (domestic literature); 23% (international literature)

• Type D: Predominantly extracranial tumor — incidence: 8% (domestic literature); 8% (international literature)

The Jefferson classification, proposed in 1959 on the basis of the segment of the trigeminal nerve involved by the tumor (Table 1), divides tumors into four types: the nerve root type, in which the tumor originates from the nerve root and is predominantly located within the posterior cranial fossa; the ganglion type, in which the tumor originates from the trigeminal ganglion and is predominantly located within the middle cranial fossa; the dumbbell type, consisting of larger tumors involving both the middle and posterior cranial fossae; and the branch type, in which the tumor involves the V1, V2, or V3 branch of the trigeminal nerve individually.

Table 1: Jefferson Classification of Trigeminal Schwannomas

Treatment Options for Trigeminal Schwannoma

As trigeminal schwannomas are benign and relatively slow-growing, several treatment strategies are available.

The most conservative approach is imaging surveillance, with repeat imaging recommended every 6 to 12 months. This strategy is primarily indicated for small tumors or elderly patients in whom the risks of surgery outweigh those of tumor growth.

Stereotactic radiotherapy is appropriate for patients in whom surveillance imaging demonstrates a growth tendency.

Microsurgical resection or transnasal neuroendoscopic resection represents the definitive treatment for trigeminal schwannoma. When gross total resection can be achieved, the risk of recurrence is low. If subtotal resection is undertaken in order to preserve neurological function, adjuvant radiotherapy should be administered.

Bilateral trigeminal schwannomas are a distinct entity, occurring exclusively in patients with neurofibromatosis type 2 (NF-2). Surgical treatment is recommended only for the symptomatic side. The contralateral asymptomatic tumor may be managed with observation or stereotactic therapy.

Preoperative Considerations and Surgical Approaches

INC International Neuroscience notes that the choice between microsurgical and endoscopic surgery for trigeminal schwannoma is primarily determined by tumor location. The Jefferson classification simplifies surgical planning for these tumors. Table 2 outlines the optimal surgical approach for each tumor type. Tumors located within or adjacent to the ganglion can generally be managed adequately via an extradural approach, which minimizes the risk of injury to adjacent cranial nerves.

Table 2: Optimal Surgical Approaches for Trigeminal Schwannomas

Given the typically soft consistency of trigeminal schwannomas, large multiloculated tumors with their predominant component in the middle cranial fossa can be approached via the middle fossa extradural approach to achieve gross total resection. This principle also applies to tumors predominantly situated in the posterior fossa that extend into the middle cranial fossa through an enlarged Meckel's cave; such tumors may be resected via a modified retrosigmoid approach.

It should be noted, however, that the surgical corridor from the posterior fossa into the middle fossa offers limited exposure. Accordingly, for trigeminal schwannomas of comparable size in both the middle and posterior fossae, the middle fossa approach should be attempted first in order to resect the entire tumor; if the posterior fossa component cannot be safely resected in full owing to surgical risk, a second-stage craniotomy via the retrosigmoid approach should be performed.

Preoperative lumbar puncture with drainage catheter placement or ventricular drain insertion is beneficial in reducing intraoperative brain tension. The use of intraoperative neurophysiological monitoring facilitates preservation of neurological function. Monitoring modalities include somatosensory evoked potentials (SSEPs) and brainstem auditory evoked responses (BAERs).

Reference: https://www.incsg.com/sanchaqiaoliu/127.html