LAUSR

An otherwise healthy 73-year-old male was referred to our head and neck unit with a constellation of left sided facial and trigeminal nerve symptoms concerning for large nerve perineural spread (PNS). His only significant skin cancer history was an incompletely excised intraepidermal carcinoma of his left temple 24 months earlier (pathology showed no perineural invasion). Five months later he developed intermittent formication over his left malar eminence which became increasingly painful to touch despite optimal analgesia. Overseeing his initial management were two GPs, a neurologist, radiologist and ear, nose and throat (ENT) surgeon who were all clinically suspicious of PNS. Two initial MR neurograms failed to radiologically identify PNS and it was not until a biopsy of his left frontal branch was performed a further 12 months later following the sudden onset of left brow ptosis was his diagnosis confirmed. Only on a third MR neurogram performed after tissue diagnosis was PNS identifiable (Fig. 1). A PET scan demonstrated no significant avid lesions or lymph nodes. The natural history of PNS is characterized by the retrograde centripetal spread away from the site of the primary tumour towards the brainstem and intracranially causing significant pain, morbidity and inevitable death within months of development. It follows that early diagnosis and treatment is key. A recent (2016) Queensland cohort of 50-patients demonstrated 65% overall survival at 5 years with clear surgical margins and adjuvant radiotherapy. When this treatment is limited recurrence free survival reduced from 62% to 38%. Factors associated with improved 5-year disease specific survival (DSS) is improved with single nerve disease (67% and 36% respectively) and limited zonal extension, 93%–85% (zone 1), 64.4% (zone 2) and 20% (zone 3). Magnetic resonance imaging (MRI) is the diagnostic modality of choice with a sensitivity of 95%. Focused studies called ‘MR neurograms’ image the anatomical pathways of cranial nerves, limit scan times and minimize movement artefact providing expert radiologists with the best available information to identify PNS which is characteristically small volume (too small for PET) and buried within the complex anatomy of the head and neck. Key diagnostic findings include (i) asymmetric nerve enhancement, (ii) asymmetry and infiltration of juxtaforaminal fat pads of the skull base and deep face (on axial and coronal T1WI sequences) and (iii) denervation changes in the muscles of facial expression and mastication (on coronal T2WI fatsuppressed sequences). In this case, the initial MR neurograms were suboptimally protocoled, with large slice thickness and spacing, causing the small volume disease to be lost or distorted following isovolumetric reconstruction. (Imaging specifics are outlined in Fig. 1). Regardless, clinical suspicion should always consider the possibility of radiologically negative PNS and trigger close interval follow-up examination and imaging or nerve biopsy. This case highlights the ongoing challenges of early diagnosis of PNS even when clinical suspicion is high. Referral to a multidisciplinary head and neck surgery team for the coordination of the diagnosis and subsequent treatment of this rare disease is recommended.