We read with interest the article by Anand et al. about a 9-year-old boy with an asymptomatic, right-sided intraparotid facial nerve schwannoma that only manifested itself 1 year before presentation.1 The patient underwent successful parotidectomy with dissection of all five branches of the facial nerve from the tumor, resulting in mild peripheral facial nerve palsy after surgery.1 The study is interesting, but some points should be discussed. The first point is that nerve conduction studies (NCS) of the facial nerves could be helpful for the diagnosis. Although the patient did not have motor deficits in the muscles innervated by the facial nerve, it is conceivable that there was subclinical involvement that could be detected by NCS, which could reveal delayed motor response latency or reduced amplitude of the compound muscle action potential. NCS could be used to distinguish whether one or more branches of the facial nerve were subclinically affected or not.2 Subclinical involvement and excitability of the facial nerve could also be documented before and after surgery by NCS or transcranial magnetic stimulation (TMS) if available. The second point is that it would be interesting to know whether or not a contrast agent was administered for the magnetic resonance imaging (MRI).1 Contrast agent should be administered not only for exclusionary diagnosis, but also because schwannomas usually show intense contrast enhancement.3 Schwannomas are also usually fluorodeoxyglucose (FDG)-avid, which is why hypermetabolism can be documented in FDG positron emission tomography (PET).4 Computed tomography angiography and digital subtraction angiography (DSA) can also be helpful in diagnosing peripheral nerve schwannoma. Did the imaging of the index patient show the characteristic “target” or “string” sign, which suggests malignancy?5 However, FDG-PET, DSA, and TMS should only be considered complementary methods for pre- and postoperatively assessment of nerve and tumor. Pediatric guidelines favor conservative approaches (observation/serial MRI) for small, asymptomatic intraparotid schwannomas unless growth or symptoms occur. The third point is that the schwannoma of the index patient should be classified according to the four Marchioni stages (Type A: resectable without nerve damage, Type B: requires partial nerve sacrifice, like a branch, Type C: needs sacrifice of the main trunk, and Type D: involves sacrificing trunk and major divisions). Was the facial nerve already infiltrated or not? The fourth point is that it should be explained why the fine-needle biopsy of the schwannoma was inconclusive.1 We should know what tissue was found in the histological examination of the biopsy. Was it fibrocytes, parotid tissue, or was a cyst biopsied? To ensure no tumor tissue is missed, a needle biopsy can be performed under ultrasound guidance. The fifth point is that it would be useful to know the long-term outcome.1 Did the slight motor deficit reported postoperatively persist? Did the patient develop fasciculations or myokymia of the muscles innervated by the facial nerve? Since the recurrence rates of schwannomas are reported to be as high as 10%, it is useful that these patients undergo regular clinical examinations and follow-up imaging. Finally, we should know which of the five branches of the facial nerve were affected after surgery. Was the patient able to close his right eye sufficiently? Did he need an eye patch for his right eye? Did the patient undergo NCS after surgery? In summary, patients with asymptomatic intraparotid facial nerve schwannomas require extensive pre- and post-operative investigations, including contrast-enhanced MRI, to assess the severity of the tumor and determine which branch of the facial nerve is affected or not. FDG-PET, DSA, and NCS can complement these examinations if available. A wait-and-see strategy is not recommended to avoid missing the point at which the nerve is destroyed or the tumor becomes malignant.6 However, the incidence of malignant schwannoma in the general population is 0.001%.6 Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Josef Finsterer (Sun,) studied this question.