Plexiform neurofibroma of parotid gland

Clinical History

A 12-year-old boy with NF1 presented with a soft, asymptomatic swelling on his right cheek. The size of the mass had increased gradually for four years. There was no history of trauma, infection or surgery.

Imaging Findings

On MR imaging, there was a large right parotid gland lesion, which extended inferiorly so that it lied adjacent to the right submandibular gland. The lesion showed intermediate signal on T1-W images (Fig. 1) and enhanced intensively after IV contrast administration (Fig. 2). On fat suppressed T2-W images the mass had a heterogeneous high signal intensity with flow voids (Fig. 3).

Discussion

Neurofibroma is a hallmark of NF1 and generally occurs initially in childhood or adolescence. NF1-associated neurofibromas are subdivided into the three types localized, diffuse and plexiform. The most common type seen with NF1 is localized neurofibroma. Plexiform neurofibromas are pathognomonic of NF1, usually appear in early childhood and precede cutaneous neurofibromas. Pathologically, a plexiform neurofibroma exhibits diffuse involvement of a long segment of nerves and its branches with tortuous expansion. Its gross appearance has been described as a “bag of worms” [1].
CT of plexiform neurofibroma displays large multilobulated masses, generally within a major nerve distribution. The lesion has low attenuation relative to muscle and enhances after contrast administration. Findings on MR imaging reveal hypointense lesion on T1-weighted images, hyperintense lesion on T2-weighted images, and avid contrast enhancement. Signal on T2-weighted images may show a characteristic target sign, consisting of a central hypointense region [2].
MR imaging of plexiform neurofibromas resemble infantile haemangiomas. Intralesional peripherally localized fat areas that are seen in infantile haemangiomas may help discriminate between these two lesions [3]. Ultrasound of haemangiomas and neurofibromas may be similar too, because both of these tumours are hypoechoic on ultrasound and show vascularization on Doppler US [4].
Plexiform neurofibromas grow along the length of a nerve and may encase multiple nerve branches, infiltrate surrounding soft tissue and cause bone hypertrophy. Removal of benign plexiform neurofibromas is frequently difficult due to encasement of surrounding structures. Consultation with experienced soft tissue tumour or plastic surgeons is essential before removal. There is insufficient evidence to support the use of drugs in patients with symptomatic plexiform neurofibromas. Because of the risk of malignancy, radiotherapy is contraindicated in benign tumours [5].

Differential Diagnosis List

Final Diagnosis

Plexiform neurofibroma of the parotid gland

URL:	https://eurorad.org/case/12548
DOI:	10.1594/EURORAD/CASE.12548
ISSN:	1563-4086