Low-grade Appendiceal Mucinous Neoplasm: A Rare Case Presentation

Abstract

Low-grade appendiceal mucinous neoplasms (LAMNs) are rare appendiceal tumors characterized by mucin production and low-grade cytologic atypia. Although benign in nature, they have malignant potential if the mucinous epithelium breaches the appendiceal wall, leading to pseudomyxoma peritonei. We report the case of a 34-year-old male who presented with abdominal pain and was diagnosed with LAMN on histopathological examination after appendectomy. The patient recovered uneventfully and remains disease-free at follow-up. This case underscores the importance of timely diagnosis and complete surgical excision to prevent complications associated with mucinous neoplasms of the appendix.

INTRODUCTION

Mucinous appendiceal neoplasms account for <0.3% of all appendectomy specimens and are often diagnosed incidentally during surgery for appendicitis. The World Health Organization (WHO) 2019 classification divides these lesions into low-grade appendiceal mucinous neoplasms (LAMNs), high-grade appendiceal mucinous neoplasms (HAMNs), and mucinous adenocarcinomas.[1] LAMNs are characterized by villous or flat epithelial proliferation with mucin accumulation, causing luminal distention. While the prognosis is excellent for lesions confined to the appendix, perforation, and spread of mucin into the peritoneum can lead to pseudomyxoma peritonei (PMP), a potentially fatal condition.[2] This report documents a rare presentation of LAMN in a middle-aged male, emphasizing histopathological evaluation and appropriate surgical management.

CASE REPORT

A 34-year-old male, was admitted to the Department of General Surgery, Dr. D. Y. Patil Hospital and Research Centre, Pimpri, Pune, on June 3, 2025, with the chief complaint of right lower abdominal pain for 6 days. The pain was dull, continuous, and nonradiating, aggravated by movement and not associated with vomiting, fever, or altered bowel habits. There was no history of weight loss, bleeding per rectum, or previous abdominal surgery. The patient’s medical history included no known allergies or major comorbidities, and he was a nonsmoker and nonalcoholic.

On clinical examination, the patient was alert and afebrile, with pulse – 82/min, blood pressure - 122/78 mmHg, and respiratory rate - 18/min. Abdominal palpation revealed localized tenderness in the right iliac fossa without rebound or guarding. No palpable mass, hepatosplenomegaly, or hernial sites were noted. Bowel sounds were normal, and digital rectal examination was unremarkable.

Laboratory investigations

Routine laboratory tests were within normal limits. The complete blood count (CBC) showed:

• Hemoglobin: 16.3 g/dL

• Total leukocyte count: 4900/µL

• Platelet count: 3.41 × 10⁵/µL

• Red blood count: 5.25 × 10⁶/µL

• MCV: 89.3 fL.

Urinalysis showed clear appearance, pH 6.0, no protein, glucose, or blood, and 1–2 pus cells/hpf. Hepatitis B surface antigen test was nonreactive, and coagulation profile (prothrombin time - 13.0 s, INR - 1.07) was within normal range. Blood group was A, Rh Positive.

Radiological findings

A contrast-enhanced computed tomography [Figure 1] (CT) (CECT) scan of the abdomen and pelvis performed on June 3, 2025 revealed an edematous, heterogeneously enhancing appendix arising from the posterior wall of the cecum, with periappendiceal fat stranding and multiple subcentimetric lymph nodes, suggesting an appendiceal phlegmon rather than abscess [Figure 2]. There was mild reactive wall thickening of the distal ileum and cecum. Ultrasonography demonstrated an ill-defined hypoechoic collection in the right iliac fossa with surrounding inflammatory changes, indicating a ruptured or inflamed appendix.

Figure 1.

Coronal computed tomography abdomen – inflamed appendix from the cecal wall

Figure 2.

Axial computed tomography abdomen – Appendiceal phlegmon

These imaging findings correlated clinically, supporting the diagnosis of an inflammatory appendiceal mass with mucinous pathology.

Surgical intervention

The patient underwent an open appendectomy on June 5, 2025 under spinal anesthesia through a McBurney’s incision. Intraoperatively, the appendix was dilated, congested, and firmly adherent to the caecum with surrounding fibro-inflammatory tissue. Careful adhesiolysis was performed to free the appendix without rupture or mucin spillage. The specimen was excised into two tissue fragments, measuring 2.5 cm and 1.5 cm, and sent for histopathological examination [Table 1]. Hemostasis was secured, and the abdominal cavity was irrigated before closure. The patient tolerated the procedure well, with no intraoperative complications or evidence of peritoneal contamination.

Table 1.

Summary of clinical, radiological, and pathological findings

Parameter	Findings	Interpretation
Age/sex	34 years/male	Young adult male
Chief complaint	Right iliac fossa pain×6 days	Suggestive of appendiceal pathology
Vitals	Stable	Nontoxic appearance
CBC	Hb 16.3 g/dL, WBC 4900/µL, Platelets 3.41×105/µL	Normal
HBsAg/INR	Nonreactive/1.07	Within normal limits
CT abdomen	Appendix with wall thickening, periappendiceal fat stranding	Appendiceal phlegmon
USG abdomen	Hypoechoic collection, inflammatory changes	?Ruptured appendix
Surgery	Open appendectomy	Specimen excised in 2 parts
HPE diagnosis	LAMN	Benign, premalignant potential
Outcome	No recurrence on 6-month follow-up	Excellent prognosis

LAMN=Low-grade appendiceal mucinous neoplasm, CBC=Complete blood count, CT=Computed tomography, HBsAg: Hepatitis B surface antigen, WBC=White blood cell, Hb=Hemoglobin, INR=International normalized ratio, USG=Ultrasound, HPE=Histopathological examination

Histopathology

Specimen

Two appendix fragments (2.5 cm and 1.5 cm) with attached periappendiceal fat [Figure 3].

Figure 3.

Gross specimen of excised appendix

Gross findings

Gray-brown external surface; lumen patent and filled with mucinous material.

Microscopy

• Lining epithelium partially stratified mucinous type with low-grade nuclear atypia

• Mucin dissection noted into the submucosa and muscularis layers

• Chronic inflammatory infiltrate composed predominantly of lymphocytes

• No evidence of serosal breach, lymphovascular invasion, or invasive carcinoma

• Tumor margins were free of neoplastic cells.

Final diagnosis

LAMN – confined to appendix, no extra-appendiceal spread.

Postoperative course

The postoperative period was uneventful. The patient was hemodynamically stable and had no signs of infection or wound complications. Oral fluids were initiated on the postoperative day 2, followed by a soft diet on day 3. Pain was well-controlled with analgesics, and bowel movements resumed normally. The surgical wound healed well, and the patient was discharged on the 4^th postoperative day with instructions for follow-up. A 6-month postoperative CECT scan showed no residual lesion, recurrence, or metastatic spread. At follow-up, the patient remained asymptomatic, pain-free, and in good general health, confirming a favorable recovery and excellent prognosis.

DISCUSSION

LAMN is a rare epithelial tumor of the appendix, representing <0.3% of appendectomy specimens. It is characterized by mucin-producing neoplastic epithelium with low-grade cytologic atypia and potential for peritoneal dissemination if the appendix ruptures.[3] The 2019 World Health Organization (WHO) classification categorizes mucinous appendiceal lesions into LAMN, HAMN, and mucinous adenocarcinoma, based on histologic features and behavior. LAMN typically presents with nonspecific symptoms, often mimicking acute appendicitis, as seen in this patient who reported right iliac fossa pain without systemic toxicity.[4] Imaging modalities like CT and ultrasonography play a crucial role in diagnosis, demonstrating a distended, thick-walled appendix with periappendiceal fat stranding or mucinous material. In this case, CT findings suggested an appendiceal phlegmon, which correlated with histopathological evidence of mucinous neoplasm confined to the appendix.[5]

Histopathological evaluation remains the gold standard for diagnosis. Hallmarks include villous or flat epithelial proliferation, mucin accumulation, and “pushing” rather than infiltrative margins.[6] The absence of lymphovascular invasion, perforation, or extra-appendiceal mucin indicates an excellent prognosis. The present case demonstrated these features, confirming the diagnosis of LAMN without evidence of invasion or PMP.[7] Surgical management depends on the extent of the disease. For lesions confined to the appendix, a simple appendectomy is curative. Right hemicolectomy is reserved for tumors involving the base of the appendix, positive margins, or nodal metastasis.[8] In cases with peritoneal spread, cytoreductive surgery and hyperthermic intraperitoneal chemotherapy may be indicated.[9]

The patient in this report underwent an open appendectomy with complete excision of the lesion and has remained disease-free for 6 months postoperatively.[10] This outcome reinforces the excellent prognosis associated with localized LAMN and highlights the importance of early detection, complete surgical removal, and vigilant follow-up to prevent recurrence or progression to PMP.[11]

CONCLUSION

LAMN, though rare, should be considered in patients presenting with atypical appendicitis or recurrent right iliac fossa pain.[12] Early surgical intervention and histopathological confirmation are critical for optimal outcomes.[13] The present case reinforces that appendectomy alone is sufficient for LAMN confined to the appendix without serosal invasion.[14] Continued postoperative surveillance is recommended to detect potential recurrence or progression to PMP.[15]

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.