PTU-057 The "poor Man's Cell-block" Sample Preparation Method For Eus-fna Of Mediastinal And Retroperitoneal Lesions Does Not Require Attending Pathology Staff Or Cytology Expertise.

INTRODUCTION: We present a novel technique of sample preparation for endoscopic ultrasound (EUS) that is simple, convenient and yields a high diagnostic success rate. EUS-guided fine needle aspirate (FNA) is increasingly used to obtain tissue in the mediastinum and retroperitoneum. Compared with surgical biopsy, EUS is minimally invasive and safe. The procedure, however is not without risk and can occasionally be poorly tolerated. It is therefore imperative that sampled tissue is optimally prepared. Ideally sample preparation should be simple without the need for an attending pathologist, and enable specific diagnosis and prognostics. The novel "poor man's cell block"(1) (PMCB) technique, recently adopted in our institution for all EUS FNA, fulfils this need. The PMCB technique allows the entire sample to be processed "as a biopsy". No slide preparation skills are needed and pathology staff need not be present. Special equipment or centrifugation is unnecessary, and samples can be reported without specific expertise or training in cytopathology. PCMB enables additional studies such as immunohistochemistry to enable subclassification and risk stratification of some neoplasms.

METHODS: All mediastinal and retroperitoneal histology/cytology reports since starting we started using the PMCB technique (2012-2013) were retrieved from the pathology database.

RESULTS: 23 mediastinal and 33 retroperitoneal reports were retrieved, of which 18 mediastinal and 27 retroperitoneal samples respectively were prepared with the PMCB technique. All of the mediastinal PMCB samples (100%) were diagnostic. Neoplasms were accurately subclassified, and several benign samples were corroborated by the presence of non-necrotising granulomas. 63% of retroperitoneal PMCB samples were diagnostic. More specific diagnoses were afforded by the PMCB technique vs cytology (stromal and perineural invasion was seen in many pancreatic PMCB samples, enabling a "definitive" invasive diagnosis). In addition, a spindle cell GIST, and well differentiated endocrine carcinoma were diagnosed and both approximately graded/risk stratified.

CONCLUSION: The PMCB technique is a simple, reliable and cost-effective EUS-FNA sample preparation technique that in our hands appears superior to conventional cytology preparations (83% diagnostic rate PMCB vs 57% cytology). We suggest PCMB can be reported by pathologists without cytology training/expertise. PMCB allows more accurate diagnosis with the additional benefit of immunohistochemistry allowing more accurate diagnosis and risk stratification for some neoplasms.

REFERENCE: Mayall, F, Darlington, A. The poor man's cell block. J Clin Pathol 63:837-838.

DISCLOSURE OF INTEREST: None Declared.