Diagnosis of feline mesenchymal nasal hamartoma by squash preparation cytology

Background
Feline Mesenchymal Nasal Hamartoma (MNH) is a rare benign tumor-like lesion of the sinonasal tract affecting young cats.
Objectives
This study aimed to determine the diagnostic significance of osteoblast-like (OB-L) and osteoclast-like cells (OC-L) in squash preparation cytology from endoscopic biopsies.
Methods
A 5-year database was retrospectively reviewed and included 109 cases of which 24 were diagnosed as MNH by histopathology. Slides were examined by two cytologists (one experienced and one inexperienced in nasal and squash cytology) in a double-blind study. The inexperienced cytologist counted OB-L and OC-L in 500 intact nucleated cells. The experienced cytologist assigned samples to four categories for OB-L (0, 1-5, 6-10, >10/field) and OC-L (0, 1-2, 3-5, >5/field).
Results
The presence of OB-L and OC-L was significantly associated (P < 0.001) with the histologic diagnosis of MNH. Receiver operating characteristic curves from the counts by the inexperienced cytologist revealed 3/500 OB-L and 2/500 OC-L as the best cut-offs for the diagnosis of MNH. Those of the experienced cytologist evaluation revealed that all the MNHs presented more than 10 OB-L/field and 3 or more OC-L/field. Both cytologists detected each cell type in all MNHs with an overall concordance of 0.93.
Conclusions
The presence of OB-L and OC-L is a consistent finding in MNH, and thus, represents a reliable cytologic diagnostic criterion. The described methods are applicable in routine in-clinic laboratory settings and are easy to apply at any expertise level. Further prospective studies are needed to assess the accuracy of the proposed cut-off values.