Transcranial trigeminal schwannoma.

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A 51-year-old man fell while hiking and sustained a mild concussion and a fractured lower leg. Computed tomography (CT) of the head detected no intracranial pathology, but it did incidentally show a mass in the fight infratemporal fossa. Additional imaging was ordered to further characterize this finding. Magnetic resonance imaging (MRI) demonstrated a complex multilobular mass in the fight masticator space (figure). The mass extended via the fight foramen ovale into the area of the right cavernous sinus. It measured 6.6 x 3.7 x 4.5 cm.

Neurologically, the patient was entirely asymptomatic. He had no history of pain, weight loss, night sweats, facial tics, hearing loss, sinus pressure, or walking difficulty. On physical examination, he was healthy appearing. Findings on the ENT examination were normal except for the mass, which was palpable intraorally in the area of the fight maxillary tuberosity. The mass was smooth and nontender.

Because the patient was completely asymptomatic, he was offered either observation or a tissue biopsy to establish the diagnosis. He opted for the latter, which demonstrated findings consistent with a schwannoma.

Schwannomas do not have a predilection for either sex. Between 25 and 45% of all extracranial schwannomas occur elsewhere in the head and neck. (1) Schwannomas of the head and neck can arise from any nerve--cranial, peripheral, or autonomic. Case series have shown that most medial neck tumors originate in the glossopharyngeal, vagus, accessory, hypoglossal, and sympathetic chain nerves, while lateral neck tumors originate in the cervical or brachial plexus nerves. (2,3)

Only about 400 cases of intracranial trigeminal schwannomas have been reported in the literature. (4,5) Moreover, fewer than 40 cases of extracranial schwannoma arising from the distal branches of the trigeminal nerve have been reported. (5-7)

The most common presenting symptom of all extracranial schwannomas is a painless neck mass; patients with a trigeminal schwannoma may also demonstrate facial dysesthesia. A painful schwannoma is unusual. When a schwannoma is associated with a neurologic deficit, malignancy must be excluded.

The primary diagnostic modality is radiography; fine needle aspiration is of limited use. Until recently, CT was the modality of choice. Today, MRI has been shown to be superior for differentiating schwannomas from other head and neck tumors, for delineating tumor spread, and for defining a tumor's relationship to neighboring structures, such as the great vessels.

Because benign schwannomas usually grow slowly, are noninvasive, and rarely recur, a conservative treatment plan is appropriate for most patients. (8) Local excision with nerve preservation via a transcervical approach is warranted for symptomatic masses in the neck. Depending on the tumor's location and the nature of symptoms, resection may be indicated for tumors in other areas of the head and neck. The avascular nature of these tumors allows for dissection within the capsule and separation from the nerve of origin. (9) For malignant schwannomas, wide excision with clear margins is recommended, although this can be difficult. Adjuvant chemotherapy, radiotherapy, or both may be warranted.

Schwannomas must be included in the differential diagnosis of parapharyngeal masses and tumors of the skull base. For those patients in whom a surgical option is considered, an understanding of the possible attendant neurologic complications is important. Fortunately, because the vast majority of schwannomas are benign, they can be managed conservatively.

References

(1.) Leverstein H, Castelijns JA, Snow GB. The value of magnetic resonance imaging in the differential diagnosis of parapharyngeal space tumours. Clin Otolaryngol Allied Sci 1995;20(5):428-33.

(2.) Colreavy MP, Lacy PD, Hughes J, et al. Head and neck schwannomas--a 10 year review. J Laryngol Otol 2000;114(2):119-24.

(3.) Leu YS, Chang KC. Extracranial head and neck schwannomas: A review of 8 years experience. Acta Otolaryngol 2002;122(4):435-7.

(4.) McCormick PC, Bellow JA, Post KD. Trigeminal schwannoma. Surgical series of 14 cases with review of the literature. J Neurosurg 1988;69(6):850-60.

(5.) Yoshida K, Kawase T. Trigeminal neurinomas extending into multiple fossae: Surgical methods and review of the literature. J Neurosurg 1999;91(2):202-11.

(6.) Nadkarni T, Goel A. A trigeminal neurinoma involving the lacrimal nerve: Case report. Br J Neurosurg 1999;13(1):75-6.

(7.) Paquis P, Castillo L, Lonjon M, et al. [Extracranial trigeminal schwannomas with middle temporal fossa development]. Neurochirurgie 1998;44(1):38-45.

(8.) Myssiorek DJ, Silver CE, Valdes ME. Schwannoma of the cervical sympathetic chain. J Laryngol Otol 1988;102(10):962-5.

(9.) Clifton MA. Sympathetic neurilemmoma: An uncommon cause of solitary cervical swelling. J R Coll Surg Edinb 1977;22(5):351-4.

Daniel H. Coelho, MD; Nilesh Vasan, MD, FRACS

From the Department of Otolaryngology, New York University School of Medicine, New York, (Dr. Coelho), and the Section of Otolaryngology, Hospital of St. Raphael, (Dr. Vasan), New Haven, Conn.