Case Presentation: A 56-year-old man with a past medical history of hypertension, hyperlipidemia, polysubstance abuse, and perforated appendicitis presented to the emergency department for one-week right lower quadrant abdominal pain. Of note, two-years prior, the patient had one-day of similar pain associated with nausea and emesis. A computed tomography (CT) scan of the abdomen and pelvis showed perforated appendicitis with a peri-appendiceal abscess, which was treated non-operatively given the inflammatory process loculated in a large phlegmon medial to the appendix, and away from the peri-appendiceal abscess. The patient improved clinically and discharged with a plan to follow-up in the outpatient setting, but unfortunately, he never followed-up for an interval appendectomy.Upon his current presentation, laboratory workup was pertinent for WBC of 10.5 x103/µL, Hemoglobin of 15.2 g/dL, and creatinine of 0.94 mg/dL. He was admitted to the hospital and underwent laparoscopic appendectomy, during which, the appendix was 4.7 x 1.8 x 1.5 centimeters (cm) in size, massively dilated with intraluminal fecalith and significant surrounding adhesions. Postoperative pain is well controlled, and he was discharged home shortly after that with outpatient follow-up. Pathology sections were consisted of large pools of mucin extending into the peri-appendiceal fat with surrounding mild chronic inflammation—picture indicating a Low-grade appendiceal mucinous neoplasm (LAMN) with extra-appendiceal acellular mucin extravasation, and concerning for pseudomyxoma peritonei (PMP). Further evaluation of the underlying tumor showed elevated carcinoembryonic antigen (CEA) at 5.29 ng/mL; CT scan of the chest, abdomen, and pelvis did not show any evidence of metastasis; screening colonoscopy reported a normal-appearing appendiceal orifice, and a 1.0 cm pedunculated polyp in the mid transverse colon at 70 cm, biopsy-proven adenomatous polyp. A robotic-assisted right hemicolectomy was performed subsequently. A tissue sample from the right hemicolectomy reported a segment of the benign colon, including terminal ileum and ileocecal valve with no residual adenomatous change, malignancy, or extravasated mucin noted; moreover, six benign pericolic lymph nodes were negative for malignancy.

Discussion: LAMN is rare, and given its variable presentations, it could be misdiagnosed as acute appendicitis. Those < 2.0 cm are usually benign, while a size > 6.0 cm signifies a risk for perforation, malignancy, and/or PMP development. In our patient, the interventional radiology (IR) specialist recommended holding off on IR-guided aspiration and drain given most of his inflammatory process was in a large phlegmon away from the peri-appendiceal abscess, ileocecal valve not fully visualized on CT imaging, and the patient’s improvement in clinical status with non-operative management.

Conclusions: Accurate histopathological evaluation is essential to assess malignancy risk, metastasis, and outcomes of patients presenting with appendicitis. Issues with patient compliance further affect the intended treatment strategy. Maintaining a high index of suspicion for the possibility of appendiceal neoplasms is crucial in deciding appropriate management modality. Further studies to determine management and monitoring strategies of LAMN are necessary, in addition to a set forth ways to better counsel patients regarding the value of compliance and follow-up is essential in improving outcomes.