Imaging of appendiceal mucinous epithelial neoplasms: A narrative review

Table 2 Differential diagnoses of appendiceal mucinous epithelial neoplasm

Diagnosis	Typical location/origin	Key imaging features (US/CT/MRI)	Helpful differential clues
Appendiceal mucocele/appendiceal mucinous epithelial neoplasm	Appendix, contiguous with cecum	Well-circumscribed ovoid or pyriform cystic mass; “onion-skin” appearance on US; low-attenuation content on CT; T2 hyperintense on MRI; mural or curvilinear calcifications; possible wall thickening or mural nodules	Continuity with cecal pole; separation from right ovary; calcified wall highly suggestive
Acute appendicitis	Appendix	Dilated appendix (> 6 mm), wall thickening and hyperenhancement, peri-appendiceal fat stranding, possible appendicolith	Lack of marked cystic dilatation; absence of mural calcifications or layered mucin
Inflamed mucocele + appendicitis	Appendix	Cystic appendiceal dilatation (> 13 mm), mural calcifications, associated inflammatory changes	Combination of mucocele features and acute inflammation; critical for surgical planning
Peri-appendiceal abscess	Peri-appendiceal region	Irregular fluid collection with thick enhancing walls, gas bubbles, surrounding inflammatory fat stranding	Ill-defined margins; lack of smooth wall and calcifications
Right tubo-ovarian abscess	Adnexa	Complex multiloculated cystic mass; thick enhancing walls; restricted diffusion; surrounding inflammatory changes	Tubal configuration; associated pelvic inflammatory disease; normal appendix
Hydrosalpinx	Fallopian tube	Tubular, elongated cystic structure; incomplete septa; “waist sign”; T2 hyperintense	Tubular morphology; separate from cecum and appendix
Ovarian mucinous tumor	Ovary	Large multilocular cystic mass; variable signal intensity (“stained glass” appearance on MRI); enhancing septa or solid components	Ovarian origin; absence of cecal continuity; more common than appendiceal mucinous epithelial neoplasm
Ovarian serous tumor	Ovary	Unilocular or multilocular cyst; papillary projections; solid enhancing components	Papillary excrescences; ascites without scalloping
Peritoneal inclusion cyst	Peritoneal spaces	Multiloculated fluid collection conforming to peritoneal recesses; ovary trapped within cyst	History of surgery/inflammation; ovary seen inside lesion
Lymphocele	Retroperitoneal or pelvic	Thin-walled homogeneous fluid collection; no enhancement; no calcifications	Post-surgical context; stable over time
Enteric duplication cyst	Adjacent to bowel	Well-defined cystic lesion; double-wall sign; no enhancement	Pediatric or incidental finding; fixed bowel relationship
Cecal carcinoma with appendiceal dilatation	Cecum	Mass-like or circumferential cecal wall thickening; secondary appendiceal dilatation	Primary cecal lesion; solid enhancing mass
Pseudomyxoma peritonei	Peritoneal cavity	Low-attenuation mucinous ascites; loculated collections; scalloping of solid organ surfaces; omental caking; peritoneal implants	Scalloping and relative small bowel sparing are highly characteristic
Lymphoid hyperplasia/inverted appendix	Cecal lumen	Well-circumscribed intraluminal lesion; cystic appearance	No mural calcifications; normal appendix externally

MRI: Magnetic resonance imaging; CT: Computed tomography; US: Ultrasound.