Low-grade appendiceal mucinous neoplasm

Case contributed by Bruno Di Muzio
Diagnosis certain


Right iliac fossa pain.

Patient Data

Age: 35 years
Gender: Female

Pelvic US (selected images)


The right ovary was not identified on this transvaginal study. Within the right iliac fossa/adnexa region, there is a large well-defined mass that has a funnel shape, with its narrow portion pointing deeper but difficult to be tracked. This mass demonstrates concentric echogenic layers with a central hypoechogenic content without any identifiable vascularity. Let ovary is normal. The uterus is unremarkable (not shown). 

CT Abdomen and pelvis


CT confirms a large fluid-filled mass in the right iliac fossa with thin and regular walls that tracks into a normal caliber appendix. There are two small flecks of calcifications on the mass wall. The right ovary is identified adjacent to the mass, displaced, but apparently not involved. No free fluid. The remainder of the study is unremarkable. 

Annotated image

Blue arrows showing the continuity of the lesion with the appendix. Yellow arrow showing the right ovary.

Case Discussion

Macroscopy: Labeled "Appendix". Appendix 55 x 9 mm. Mesoappendix 20 x 8 mm. Mucosa appears pale tan/cream and mildly congested. Within lumen there is grey/tan gelatinous substance. No perforation or lesions are identified. Proximal margin inked green.

Microscopy:  Sections through the appendix show replacement of normal mucosa architecture by an undulating mucinous epithelium exhibiting low-grade dysplastic change. There is atrophy of the underlying lamina propria and submucosa. Focally, there is disruption to the epithelial surface with pools of acellular mucin extending into the appendiceal wall to the junction of submucosa and muscularis propria. Mucin pools are also identified within subserosal connective tissue; however transmural dissection of mucin is not seen in the sections examined. The neoplasm appears clear of the proximal resection margin. High-grade dysplasia and invasive malignancy are not identified.

Conclusion:  Low grade appendiceal mucinous neoplasm, clear of resection margin.

Low-grade appendiceal mucinous neoplasms, previously known as appendiceal mucinous cystadenomas, are rare mucinous tumors of the appendix showing low-grade cytologic atypia.

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