Intramuscular corpora amylacea adjacent to ileal low-grade neuroendocrine tumours (typical carcinoids): a light microscopic, immunohistochemical and ultrastructural study

Abstract

AimsThe purposes of this study are to (1) document the prevalence of intracytoplasmic inclusions adjacent to ileal well-differentiated neuroendocrine tumours (WNETs), (2) examine whether and how tumour and patient characteristics are associated with inclusions and (3) investigate their properties on special stains and electron microscopy in comparison with corpora amylacea (CA).MethodsWe examined the resection slides from 26 ileal, 5 gastric and 5 rectal cases of WNET. Inclusions were readily identified with H&E staining. Histochemical, immunohistochemical and ultrastructural evaluations were performed on the block with the highest number of inclusions.ResultsIntracytoplasmic inclusions occurred adjacent (<1 mm) to 15 of 26 (57.7%) ileal WNETs. Patients with and without inclusions were of similar mean ages (59.5 vs 57.4 years; p=0.88), but NETs with inclusions were larger than those without inclusions (3.3 vs 1.7 cm, p=0.03). Inclusions were neither associated with gastric (mean age=65 years, mean diameter=1.5 cm) or rectal WNETs (mean age=47.8 years, mean diameter=0.5 cm) (p=0.01), nor were they present >1 mm from ileal NETs. CA stained strongly for ubiquitin, DPAS and Alcian blue; faintly and peripherally for desmin and smooth muscle actin and negatively for calcium. Ultrastructurally, their appearance was consistent with filaments, some with cores of particle matter.ConclusionsOur results suggest that these inclusions are virtually identical to CA and present adjacent to the majority of ileal WNET. They may be the result of a degenerative process, possibly due to chronic myocyte stress from an infiltrating slow growing tumour mass or local hormonal effects.