Guidelines for validating whole slide imaging (WSI) for primary diagnosis in surgical pathology have been recommended by an expert panel commissioned by the College of American Pathologists. The implementation of such a system using these validation guidelines has not been reported from the community hospital setting. The objective was to implement a WSI system, validate each pathologist using the system and run the system in parallel with routine glass slide interpretation. Six pathologists re-reviewed approximately 300 previously diagnosed specimens each, divided equally between glass slides and digital images (scanned at ×20). Baseline intraobserver discordance rates (glass to glass) were calculated and compared to discordance rates between the original glass slide interpretation and the reviewed digital slide interpretation. A minimum of 3 months was used as the washout period. After validation, a subset of daily cases was diagnosed in parallel using traditional microscopy (TM) and WSI over an 8-month period. The TM and WSI discordance rates ranged from 3.3% to 13.3% and 2.1% to 10.1%, respectively. There was no statistically significant difference among the pathologists. The parallel study yielded similar rates of discordances. In our laboratory, after appropriate implementation and training, there was no difference between the WSI and TM methods.

Rationale:Primary thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TL-LGNPPA) is an extremely rare malignant nasopharyngeal tumor with features resembling papillary thyroid carcinoma including nuclear positive expression of thyroid transcription factor-1 (TTF-1).Patient concerns:A 64-year-old male presented with nasal bleeding and a foreign body sensation of the nasopharynx. Laryngoscopy revealed a 2.0-cm broad-based mass with a smooth surface on the posterior wall of the nasopharynx. A biopsy was obtained.Diagnoses:Histopathologic examination demonstrated tumor cells arranged in both papillary and glandular architecture. The tumor cells express nuclear immunoreactivity for TTF-1. The diagnosis of TL-LGNPPA was made.Interventions:After the patient was diagnosed with TL-LGNPPA, he underwent complete surgical resection.Outcomes:There was no recurrence or evidence of metastatic disease at the 12-month follow-up.Lessons:TL-LGNPPA is easy to misdiagnose as metastatic papillary thyroid carcinoma or other relative primary adenocarcinomas. It is important to have a broad differential diagnosis and know the key features of each entity because the prognosis and clinical treatment of each may differ.

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