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Case reports

A 60-year-old man with extensive sun exposure in the past presented with a 1-year history of progressive paresis involving the upper division braches of the left facial nerve. A cutaneous preauricular mass was biopsy positive for squamous cell carcinoma (SCC). Before the biopsy, a 1.5 Tesla (T) magnetic resonance imaging (MRI) indicated the presence of the preauricular nodule without any evidence of invasion. Physical examination revealed a 3 cm left preauricular biopsy site long inferior to the left lobule. The left facial nerve was intact along its lower branches, but his left brow was immobile, and he was unable to close his left eye. There was no cervical lymphadenopathy. Further radiologic evaluation using a 3-T MRI ( Fig. 1 A and B) revealed linear enhancement of the distal facial nerve branches and asymmetric enhancement in the left stylomastoid foramen, which was not evident on the 1.5-T MRI ( Fig. 1 C and D).

(A) Axial T1 postgadolinium with fat saturation 3.0-T MRI demonstrating asymmetric enhancement of the descending portion of the left facial nerve at the stylomastoid foramen (arrow), compared with the right side. (B) Axial T1 postgadolinium with fat saturation 3.0-T MRI demonstrating asymmetric linear enhancement of the left parotid gland (arrow) corresponding to motor branches of the left facial nerve. (C) Axial T1 postgadolinium with fat saturation 1.5-T MRI, demonstrating the descending portions of the bilateral facial nerves (arrows) at the stylomastoid foramina with no difference in enhancement. (D) Axial T1 postgadolinium with fat saturation 1.5 Tesla MRI, demonstrating the unremarkable appearance of bilateral parotid glands.

The patient underwent a left mastoidectomy, radical parotidectomy including overlying skin, facial nerve sacrifice, and left neck dissection. Despite the absence of tumor on gross examination, frozen sections revealed perineural invasion (PNI) at the stylomastoid foramen and in the distal left frontal branch. Further nerve resection was undertaken until negative frozen margins were obtained. Final pathology revealed invasive moderately differentiated SCC, involving papillary dermis, reticular dermis, and subcutaneous tissue of the overlying cheek skin. All surgical margins were clear. Perineural and intraneural tumor invasion were noted in the periparotid soft tissue ( Fig. 2 ). All removed lymph nodes were negative for tumor.

Hematoxylin and eosin stain at 10X demonstrating perineural invasion. (N) = Nerve. (T) = Tumor cells of squamous cell carcinoma.

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Comment

Most cases of parotid gland SCC represent metastases from cutaneous lesions. These tumors tend to reside within periparotid lymph nodes rather than within the parotid parenchyma. Cutaneous SCC of the overlying skin can also directly invade the parotid gland. Irrespective of the origin, the confluence of sensory and motor nerves within this region mandate careful evaluation for PNI. Cutaneous SCC with perineural or intraneural invasion has a poor prognosis . Histologic evidence of PNI has a 5-year local control rate of 87%, whereas histologic plus clinical evidence of PNI has a 5-year local control rate of only 55% .

In comparison to traditional magnetic field strengths (1.5 T), high-field magnets, such as those used in 3-T scanners, offer improved spatial resolution due to higher signal intensity and increased signal-to-noise ratio . High-field MRI scanning may thereby offer more sensitive presurgical staging of upper aerodigestive tract malignancies with neurotropic tendencies, including cutaneous SCC, noncutaneous SCC, melanoma, and adenoid cystic carcinoma.

In this case, a preoperative high-field MRI detected PNI, thereby explaining the corresponding clinical symptoms and further assisting in surgical planning. PNI in the setting of cutaneous SCC is associated with significantly decreased overall survival , and as such, the presence of PNI is proposed as a staging factor in parotid cutaneous SCC . Accordingly, a more precise radiologic assessment of PNI may permit improved accuracy in the staging of patients. Careful assessment using imaging techniques, such as gadolinium-contrast MRI with fat suppression, is essential in the radiographic detection of occult PNI .

Pretreatment assessment of PNI by high-field MRI may offer several advantages including: facilitating informed consent discussions, identifying the presence of occult tumor spread, determining the extent of resection, and planning future radiotherapy. Furthermore, with regard to noncutaneous head and neck SCC, PNI on histologic evaluation directs the utilization of chemotherapy and adjuvant radiotherapy . Lastly, radiologic evidence of PNI offers prognostic information. Individuals with radiologic evidence of PNI have a poorer prognosis than those with image-negative PNI .

In summary, because PNI is a strong prognosticator of tumor behavior, improvements in pretreatment PNI detection are necessary. Further research regarding PNI evaluation by high-field MRI for cutaneous SCC and other neurotropic head and neck tumors may improve critical surgical and treatment planning.