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E1941. Appendiceal Mucocele: Multimodality Case-Based Imaging Review with Pathologic Correlation
Authors
  1. Eseosa Bazuaye-Ekwuyasi; University of Texas Medical Branch
  2. Milin Rana; University of Texas Medical Branch
  3. Paul Young; University of Texas Medical Branch
  4. Julum Nwanze; Tulane University School of Medicine
  5. Peeyush Bhargava; University of Texas Medical Branch
  6. Nicolaus Wagner-Bartak; The University of Texas MD Anderson Cancer Center
Background
Appendiceal mucocele is a macroscopic description for a mucin filled distended appendix[1]. Mucinous lesions of the appendix are classified histologically as either non-neoplastic or neoplastic with mucinous neoplasm of the appendix being further subcategorized as serrated polyps, low-grade appendiceal mucinous neoplasms (LAMNs), high-grade appendiceal mucinous neoplasms (HAMNs), and mucinous adenocarcinomas[1,2].

Educational Goals / Teaching Points
In this exhibit, we review the imaging features of appendiceal mucocele using multiple modalities including ultrasonography and computed tomography (CT) and discuss possible complications. We also illustrate the appearance of appendiceal mucocele on colonoscopy. Using high-power and low-power micrographs, we depict the histologic features of the pathological subtypes of mucocele of the appendix.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Appendiceal mucoceles may be noted incidentally at surgery or on imaging. Patients may present with symptoms of acute right lower quadrant abdominal pain, resembling acute appendicitis; or those associated with the complications of mucocele [1]. Imaging findings of appendiceal mucoceles include a well-circumscribed, round or tubular, hypo-attenuated dilated cystic mass on CT or ultrasound [1,3,4]. Internal hyperechoic curvilinear layers known as onion skin sign, may also be seen on ultrasound [1]. Mural calcifications which may be appreciated on radiographs, CT or ultrasound [3] are present in less than 50% of cases [4]. Some imaging features such as wall irregularity and soft-tissue thickening may preoperatively predict a malignant appendiceal mucocele [4]. On colonoscopy, an appendiceal mucocele may appear as a rounded, protruding extrinsic mass with normal overlying mucosa [5]. The appendiceal orifice may also be seen within this elevation of the cecal wall; referred to as volcano sign [5]. Imaging is also important in ruling out differential diagnoses, especially in female patients, where appendiceal mucinous lesions should be differentiated from tubo-ovarian abscess and cystic ovarian neoplasms by identifying a normal right ovary [1,3]; and detecting possible complications such as intestinal or ureteral obstruction, intussusception, torsion, and pseudomyxoma peritonei [1,3].

Conclusion
Appendiceal mucocele is an imaging diagnosis which may result from a variety of histologic abnormalities. Familiarity with the imaging appearance, preoperative identification of imaging features suggestive of a malignant etiology and recognition of possible complications are of utmost importance to the clinician in order to appropriately manage this ambiguous pathology.