Corpora amylacea in gastrointestinal leiomyomas: a clinical, light microscopic, ultrastructural and immunohistochemical study with comparison to hyaline globules.

CONTEXT: Corpora amylacea (CA) are inclusions with starch-like composition that occur in various conditions. We have observed CA in gastrointestinal leiomyomas (GILM) and hypothesised that they differ from intracytoplasmic hyaline globules (HG) of GILM. We aimed to investigate the anatomical distribution, prevalence, staining characteristics and ultrastructural features of CA and compare them with HG of GILM. DESIGN: Slides from a consecutive series of resected GILM and bland spindle cell tumours were examined for CA and HG. Special stains, electron microscopy and elemental analysis were performed on select leiomyomas. RESULTS: CA occurred in 13/35 GILM (37%) from the following sites: oesophagus (4/8), stomach (5/7) including one frozen section, small intestine (1/2) and large intestine (3/18), but were not identified in 19 gastrointestinal stromal tumours (12 gastric, 7 small intestinal; p=0.0019), five schwannomas (three gastric, two small intestinal; p=0.154) and 35 non-GILM (p=0.0001). The densities of CA ranged from one per 4-200 mm(2). CA stained intensely with periodic acid Schiff after diastase predigestion (PASD), Alcian blue and ubiquitin, and faintly in peripheral zones for desmin and smooth muscle actin. Ultrastructurally, CA consisted of an electron-dense outer layer and a fibrillar core with scattered particle matter. HG were present in all leiomyomas, but showed variable staining for PASD, negative staining for Alcian blue and ubiquitin, and positive staining for smooth muscle markers. CONCLUSIONS: CA are a distinctive histological feature of approximately one third of GILM with different composition to HG. These differences may represent divergent degenerative processes or different stages of a single degenerative process over time.