Characterisation of Kürsteiner canals of parathyroid: imparting relevance to a one‐and‐a‐quarter‐century‐old concept.

Aims Methods and results Conclusions Kürsteiner canals (KC) were described at least 125 years ago as pharyngeal pouch embryological remnants of parathyroid and thymic development. While considered precursors for a subset of parathyroid cysts and salivary heterotopias (SH), they remain enigmatic. We now define a comprehensive phenotype of KC remnants and investigate their role in a spectrum of parathyroid lesions.`Sixty‐two cystic and 22 non‐cystic parathyroid lesions (73 patients) were retrieved from our institutional archive (2011–23) and evaluated for the presence of KC and prevalence of KC phenotype in parathyroid hormone (PTH)‐positive and PTH‐negative cysts. KC phenotype was defined as: cysts and tubules with surrounding sclerosis; bland, unilayered lining with frequent nuclear indentation of lumina; vesicular chromatin relative to chief cells; attenuated eosinophilic to ‘hyper‐cleared’ cytoplasm; and staining pattern PTH‐negative, SOX‐10‐positive, CK7‐positive, GATA‐3‐positive and PAX‐9 dim, a subset with oestrogen/progesterone receptor (ER/PR) positivity. Thirty PTH‐negative cysts were identified in the neck/mediastinum; 14 of this group also showed SH. Thirty‐two PTH‐positive cysts included: 11 cystic parathyroid adenomas, 17 hyperplastic parathyroids, and four carcinomas. KC showed two distinct subtypes and were often found near PTH‐negative cysts. PTH‐negative cysts were associated with inferior parathyroids, SOX‐10 positivity, fibrosclerosis, vesicular nuclei indenting cyst lumina and hyper‐cleared or attenuated eosinophilic cytoplasm.KC are common in parathyroids and show a distinct histological and immunohistochemical profile, with an inferior predilection favouring branchial cleft III distribution. Diagnostically, the high prevalence of this phenotype in PTH‐negative cysts and salivary heterotopia supports derivation of non‐functioning cysts from KC. Conversely, PTH‐positive cysts are more compatible with cystic change within hyperfunctioning glands. [ABSTRACT FROM AUTHOR]