Low-grade appendiceal mucinous neoplasm (LAMN) is a rare condition, characterised by a distended, mucous-filled appendix, occurring in 0.3% of appendectomies. Perforation of the mucocele can result in pseudomyxoma peritonei, which has a 10 year survival as low as 21%.

A 61 year old male presented with a two day history of gradual onset RIF pain, becoming constant in nature. There was no change to bowel habit. His BMI was 34.6. Medical history included type 2 diabetes, hypertension, obstructive sleep apnoea, and stroke. On admission he was apyrexic, and slightly hypotensive, but not tachycardic. On examination the abdomen was soft, without tenderness. Further investigation showed an AKI stage 1, WCC 13.9X109, neutrophils 11.8x109and CRP 46mg/L.

CT of the abdomen revealed an appendix mucocele, with peripheral high attenuation at the caudal aspect of the mucocele, and without any associated inflammation or collection. A laparoscopic appendectomy was performed the day after presentation, at which point the appendix was intact, and dilated with mucus to a size of 70x42x38mm.

Macroscopically, the appendix was dilated, measuring 42mm in diameter, and had been disrupted at the tip with extrusion of mucous. Microscopically, the appendix showed mucinous epithelium with undulating and filiform villous architecture, and low-grade dysplasia. These features are in keeping with a LAMN. Focally, the epithelium was attenuated and mucin involved the subserosal tissue, but did not breach the serosal surface. The patient went on to have a right hemicolectomy as a spreading villous adenoma with low-grade dysplasia was found at follow-up colonoscopy.