Discussion
Neurogenous tumors are rare amongst children, comprising only 2% of
benign non-lymphadenomatous lesions.4 Pediatric
cervical vagal schwannomas are especially rare. The median age of
diagnosis is 44 years in vagal schwannoma patients undergoing
surgery.2 The median maximum diameter of these tumors
is 5 centimeters.2 Cervical schwannomas grow at a rate
of 3 millimeters per year, and usually only become symptomatic once
large enough to cause compressive symptoms.1 Our
patient’s young age of 11 years old, in tandem with the large size of
the lesion, makes her presentation extraordinarily uncommon.
Schwannomas arise from a single nerve fascicle and may cause cranial
nerve dysfunction by exerting pressure on other fibers of the affected
or local cranial nerves. Reported series to date differ widely on the
prevalence of cranial nerve deficits at presentation. Interestingly, our
patient did not exhibit signs of vagus nerve dysfunction, despite the
nerve being involved intraoperatively, while she did have a
long-standing hypoglossal nerve palsy, seemingly due to extrinsic
compression from the vagal schwannoma. Although schwannomas do not
typically present with cranial nerve palsies, when they do, dysfunction
is usually of the index cranial nerve. Cranial nerve palsy may be
suggestive of compression in a confined space or malignant schwannoma.
Our patient’s presentation with a hypoglossal nerve palsy with intact
vagal nerve function in the context of a benign vagal schwannoma is,
therefore, unusual.
Surgical resection is the preferred treatment modality for vagal
schwannoma, either with gross total resection or intracapsular
enucleation. Gross total resection may be superior to enucleation with
respect to cure, but often results in loss of ipsilateral vagal function
distal to the lesion. Enucleation may have superior outcomes vis-à-vis
preservation of vagal nerve function, but is generally reserved only for
small schwannomas and is thought to be associated with higher rates of
recurrence.
The transcervical approach is the most commonly employed technique to
access vagal schwannomas.2 Our combined
transcervical-mandibulotomy approach was necessitated by an inability to
safely gain access to the superior aspect of the tumor due to close
adherence to the jugular foramen/skull base and adjacent, displaced
critical vascular structures. Mandibulotomy allowed for improved access,
safe mobilization of the tumor, and dissection of vessels at the level
of the skull base.
Vagal schwannoma can arise in the context of genetic syndromes,
including Neurofibromatosis Type 2, Carney’s Complex, and
schwannomatosis, with mutations in NF2 , SMARCB1 ,LZTR1 , PRKAR1a previously described. Genomic changes in
these genes all lead to downstream alterations in the production or
function of the protein merlin, which plays a role in a range of growth
factor pathways.1 Our patient demonstrated no germline
mutation or syndrome. Memorial Sloan Kettering Integrated Mutation
Profiling of Actionable Cancer Targets (MSK-IMPACT) identified an
isolated TET1 deletion of exons 1 and 2. TET1 plays a role
in epigenetic tumorigenesis and may be implicated in
schwannomatosis.5 The clinicopathologic significance
of the alteration in the setting of pediatric vagal schwannoma is
unclear.