Histopathologic study of Mucinous lesions of the appendix

Introduction: Mucinous lesions of appendix are rare with an incidence of about 0.2 to 0.7% of all the appendicetomy specimens. The mucinous lesions of appendix range from simple retention cyst to malignant mucinous adenocarcinoma. Majority of mucinous appendiceal neoplasia are epithelial type (70%) with circumferential involvement of mucosa. Peritoneal seeding and pseudomyxoma peritonei can occur with both frankly malignant as well as low-grade appendiceal neoplasms. Nearly 50% of appendiceal malignancies present clinically as acute appendicitis and can be detected by imaging modalities. Aim of this study is to analyse the incidence, age and sex prediliction, clinical presentation and histopathology of mucinous lesions of appendix. Materials and Methods: It is a reterospective study of all the mucinous lesions of appendix diagnosed at Dept. of Pathology, Kamineni Academy of Medical Sciences and Reserch Centre (KAMSRC) from 20132017. Clinical details and relevant radiological investigations are noted from case sheets. Microscopic examination is done on slides stained with routine H & E and AB-PAS. Diagnosis and classification is based on WHO 2010 and recommendations in the AJCC 8th edition. Results: Mucinous lesions accounted for 0.8% (10/1200). of all appendicetomy specimens. The study included 10 cases of mucinous lesions of appendix(10 cases): Simple mucocele (2 cases), Benign mucinous adenomas(3 cases), Low grade Appendiceal Mucinous Neoplasm (LAMN) with pseudomyxoma peritoni (PMP) (1 case), Mucinous cystadeno carcinomas (4 cases). Benign lesions are seen in females and at a younger age as compared to malignancies which are common in males and at a older age. Most common presentation is abdominal pain followed by appendicitis. Mucosal hyperplasia and high grade appendiceal mucinous neoplasms(HAMN) are not seen in our study. Conclusion: Mucinous lesions of appendix are rare. They are more common in females and associated with non-specific clinical features. Histopathology is critical for establishing diagnosis, further management and prognostication of all the mucinous lesions of appendix. © 2020 Published by Innovative Publication. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by/4.0/)


Introduction
Mucinous lesions of appendix are rare and account for 0 .2 -0.7% of all appendicetomy surgeries. [1][2][3][4][5] T hey are complex, diverse group of epithelial neoplasms ranging from simple mucoceles to complex pseudomyxoma peritonei. In 1842, Rokitansky first described mucocele as a dilatation of the appendiceal lumen by an abnormal mucus accumulation. 6 Morphologically mucocele refers to cystic dilatation of In this study, we evaulated clinical, radiological and histopathological findings of all the mucinous lesions of appendix.

Materials and Methods
It is a retrospective study carried out at KAMSRC from 2013 to 2017 over a period of five years. It included ten cases of mucinous lesions of appendix. Clinical details and radiological findings were retrieved from case sheets.
All the specimens are collected in 10% neutral buffered formalin (NBF). Gross examination findings are noted in all the cases and the sections are taken accordingly. Sections are stained with Hematoxylin & Eosin (H&E). Special stain for mucin was done with AB-PAS as and when required. Diagnosis and classification is based on WHO 2010 7 and recommendations in the AJCC 8th edition. 8

Results
Mucinous lesions of appendix are rare and accounted for 0.8% of all the appendicetomy specimends. Benign lesions include simple mucoceles or retention cysts and benign neoplastic adenomas. Malignant lesions include invasive adenocarcinomas.
Benign lesions are more common than malignant lesions and account for 50% of all lesions. All the benign lesions are seen in females at a younger age in contrast to malignant lesions which are seen in males at an older age.
All the patients presented with clinical features of appendicitis (4 cases), pain abdomen (4 cases), abdominal pain and mass (2 cases) Simple Mucocele (Retention cyst) are seen in 2/10 cases. One case was seen in 26 years female who presented with chronic appendicitis and underwent interval appendicectomy. Other case is seen in 35 years female with dilated appendix. Gross examination revealed dilated appendix filled with mucoid material. Histopathology showed dilated lumen filled with mucinous material, lined by single layered, flattened epithelium. There is no proliferation or atypia of the lining epithelium.
The 2010 WHO classification recognizes 3 main categories of mucinous neoplasms: mucinous adenoma, LAMN and appendiceal adenocarcinoma. 7 Benign mucinous adenomas accounted for 33% (3/10) cases ( Figure 1). All the cases are seen in females with mean age of 44 year. Two cases clinically presented as appendicitis and one case presented with abdominal pain. Imaging revealed dilated appendix in two cases. One case was diagnosed as mucocele on ultrasonography. Gross examination revealed dilated appendix filled with mucin. Microscopy shows appendiceal mucosa thrown into villous architecture, composed of benign columnar cells with stratification and abundant mucin and is confined to mucosa with no evidence of invasion beyond muscularis mucosa.
Low grade appendiceal mucinous neoplasm (LAMN); One case 1/10 of LAMN is seen in our study. It is seen in 36 years female who presented with abdominal pain and mass and ultrasound revealed dilated appendix. Gross examination revealed dilated appendix of 6x7cm. filled with mucin. Histopathology revealed w ell differentiated adenoma with acellular mucin dissecting the musclaris propria of appendix. There is flattened epithelial growth with loss of muscularis mucosae and mild fibrosis of submucosa.In our study, LAMN is associated with low grade pseudomyxoma peritonei (PMP) with pools of mucin and scaterred epithelial cells showing low grade cytological atpia in seperately received omental biopsy Mucinous cystadenocarcinoma is seen in 4 cases accounting for 40 % cases ( Figure 2). All are males with a mean age of 60 yrs. Abdominal pain is the most common symptom. Imaging findings showed perforated appendix in two case s and growth at the base of the appendix in other case, Grossly the appendix is markedly enlarged with serosal congestion in all cases and two cases revealed perforation. Microscopy is characterised by invasive neoplastic glands with high grade cellular atypia and nuclear pleomorphism and mitotic activity extending into muscularis propria.
Mucinous hyperplasia and High grade appendiceal mucinous neoplasm(HAMN) are not encountered in our study Summary of all the cases:

Discussion;
Primary tumors of the appendix are rare and represent less than 2% of surgical appendectomy specimens 9 They include epithelial tumors, carcinoid tumors, mesenchymal tumors, lymphomas. Mucinous neoplasms of the appendix are still rare and second only to carcinoids 10 Mucocele of the appendix can result from obstruction of appendiceal ostium due to mucus, mucuous hyperplasia, benign and malignant lesions. Other causes include fecal impaction or polyps of the cecum, inflammation from surrounding tissues 1 and rare causes found in the literature are endometriosis and metastatic melanoma. 11,12 Presently the term mucocele is only used for the macroscopic description or for imaging and as a clinical term, never as a definitive diagnosis Mucoceles of appendix are divided into four types based on histology: (1) simple retention cysts, (2) mucosal hyperplasia, (3) mucinous cystadenoma, and (4) mucinous cystadenocarcinoma. 1 Simple mucoceles are retention cysts, characterised by accumulation of mucus with normal epithelial lining and rarely exceed 2 cm. 13,14 They result from an obstructing fecolith, extrinsic compression or inflammatory conditions and rarely endometriosis.
Mucinous neoplasms of appendix include Mucinous adenoma, Low-grade appendiceal mucinous neoplasm and Mucinous adenocarcinoma. Salient features of these three entities is summarised in Table 2 There are no cases of Mucinous hyperplasia and High grade appendiceal mucinous neoplasm in our study.
Mucinous lesions of appendix are rare and accounted for 0.8% (10/1200) of all the appendicectomy specimens in our study. This is in comparision to other studies where they represented 0.2 -0.7% of all appendicetomy surgeries [1][2][3][4][5] Benign mucinous lesions are more common than malignant lesions similar to studies by Morano et al and Higa et al 1,20 In our study, Male to female ratio is 2:3. This is in contrast to other studies by Carr NJ et al. 16 which showed a male predominance (5 : 2). But in comparision to a retrospective study of 135 patients by Omari et al. 10 where 55% were females Benign and mucinous lesions as a whole are more common in females as comparable to study by Morano WF. 20 Higa et al 1 Mucoceles and mucinous cystadenomas are seen in females and all the mucinous adeno carcinomas are seen in males. However, AM are considered to occur more frequently in women. 21 Mucinous cystadenomas have high frequency in women compared to men with a ratio of 4:1, and it tends to affect patients over 50 years of age. 6 Other tumors of the gastro intestinal tract, ovary, breast and kidney can be associated in up to one-third of the patients. 21 Omari et al. recommend surveillance colonoscopy in patients with diagnosis of neoplastic mucinous lesions of appendix. 21 All the cases of adeno cacinoma are seen in males and in the sixth decade similar to study to Tirumani et al. 17 They have an increased association with other colonic neoplasia and chronic ulcerative colitis but such association is not seen in our study.
Mean age of presentation of mucinous cystadenoma is 44 years, mucinous cystadeno carcinoma is 56.7 years. Cystadenocarcinomas are seen at a later age than cystadenomas similar to other studies The most common clinical presentation is nonspecific abdominal pain as seen in 60% of cases similar to study  Mostly clinical presentation is rather non-specific making preoperative diagnosis difficult. Preo perative diagnosis is possible with the help of radiological investigations (abdominal USG, CT, or MRI) when there is cystic dilation of the appendix, mural calcification of the appendix wall, luminal diameter greater than 15mm. Macroscopic appearance of the appendix examined intraoperatively gives a clue to the diagnosis. Histopathological examination of the specimen. [23][24][25] enables the establishment of final diagnosis. In our study, USG was done in all the cases which revealed a dilated appendix. CT scan was done in one case of adeno carcinoma which showed growth at the base of appendix.
Simple retention cyst of appendix is non-neoplastic dilated appendix filled with mucin. There are two cases in our study.
Histopathology showed flattened lining epithelium with no atypia.
Most of the benign mucoceles are asymptomatic. These are mostly detected incidentally during ultrasonography, computed tomography and other radiographic examinations of gastrointestinal tract, or during a laparotomy. 5 Simple appendectomy is the treatment of choice for simple mucoceles.

Mucinous adenomas
Adenomas show female predominance and typically occur in fifth decade but the age range is wide.1Abdominal pain that mimics acute appendicitis is the most common clinical presentation.1 It can also present as an abdominal mass or as intussusception of the appendix or can be asymptomatic.
Grossly, appendix is dilated and filled with mucin. The serosa is smooth with absent mucin.
Microscopic examination reveals tumors limited to mucosa with intact muscularis mucosae. There is no mucin dissecting into the wall or mucin extrusion outside the appendix. The tumor consists of a proliferation of mucinous epithelial cells thrown into villi.
Appendiceal adenomas are benign and are treated by appendectomy alone.

LAMN with pseudomyxoma peritoni
Low-grade appendiceal mucinous neoplasm (LAMN) is a rare malignancy accounting for 1% of gastrointestinal neoplasms and is found in less than 0.3% of appendectomy specimens. 26,27 In our study only one case is seen accounting to 0.1% of all appendicetomy specimens.
They are commonly seen in men, particularly in the sixth decade in contrast in our study where LAMN is seen in 36 years female w ho presented with abdominal pain and mass. Other symptoms include abdominal pain, intussusception, and obstruction and some times asymptomatic.
Complications of LAMN include intussusception, ureteral obstruction, volvulus, small bowel obstruction (SBO), rupture, and PMP 26,27 In our case, it is associated with low grade PMP. PMP refers to the accumulation of mucin within the peritoneal cavity secondary to mucinous epithelial neoplasia. This most often occurs because of peritoneal spread of a mucinous neoplasm from the appendix but has been described with mucinous tumors from other sites, including colon, ovary, gallbladder, pancreas, and urachus.
Imaging modalities for diagnosis include ultrasound (USG) and CT. In our case, USG w as done which showed dilated appendix and CT scan revealed PMP.
Grossly, LAMN shows markedly dilated appendix filled with mucin. There is hyalinization and fibrosis of the appendiceal wall. [26][27][28] LAMNs less than two centimeters (cm) are rarely malignant. Masses larger than 6 cm have higher risk of malignant cells, a higher risk of appendiceal perforation, and development of PMP. 27 Histopathology shows low grade atypical glandular cells and epithelial cells with " pushing invasion " of atypical cells creeping into the appendiceal wall with possible diverticular formation. 28 In our case, histopathology showed mucin pools and strips of cells on the serosal surface Management of LAMN includes the prevention of rupture, seeding, and development of PMP. 27 Right hemicolectomy with or without omentectomy is recommended when there is infiltration of malignancy into submucosa or with the presence of lymph node metastasis. 29

Mucinous adeno carcinoma
Adenocarcinomas of the appendix are rare entities, representing <0.5% of all gastrointestinal malignancies and 4-6% over lesions of the appendix neoplasm 9. Collins et al 30 found an incidence of 0.082% among 50 000 appendectomy specimens. There is an increased incidence among men in some series8, 18 but not in others. 19,31 Patients usually present in fifth to seventh decade of life 18,31 and us ually as acute appendicitis. Other less common modes of presentation include a palpable mass, obstruction, gastrointestinal bleeding, or symptoms.
Appendiceal adenocarcinomas are classified as adenocarcinoma not otherwise specified, mucinous adenocarcinoma, signet ring cell adenocarcinoma, and undifferentiated carcinoma. Only Mucinous adenocarcinoma are included in our study.
Invasive adenoca rcinoma of the appendix is surgically treated by right hemicolectomy and lymph node dissection, in order to stage the tumor and ensure complete resection. 19 In our study all the cases are diagnosed on histopathology of appendicetomy specimens. Right hemicolectomy was advised in all the cases. Further follow-up details are not available.
Comparitive study of age, M :F ratio, clinical presentation of mucinous adeno carcinoma with other studies is summarised in Table 3.

Conclusion
Mucinous lesions of appendix are rare. Mucinous lesions range from simple mucocele to mucinous adenocarcinomas. They are more common in females. Most of them present with non-specific abdominal pain making preoperative clinical diagnosis difficult. Imaging shows dilated appendix. Intra operative gross examination gives us a clue to diagnosis. Final diagnosis is established by histopathological study of the excised specimen. Neoplasms confined to the mucosa of the appendix are adenomas, whereas neoplasms extending beyond the appendix can be LAMNs or adenocarcinomas. The treatment for simple mucocele is appendectomy.
Right hemicolectomy is advised for intermediate /malignant lesions depending on the size and location. Maximum care should be taken to avoid intraperi toneal rupture of a mucocele because of the risk of PMP. Risk of developing adenocarcinoma in colon, ovary, endometrium, breast, kidney is greater in patients with a mucocele than in the general population, warranting regular cancer survillence and monitoring in these cases. Clear communication between the radiologist, pathologist and surgeon is essential for optimal patient management.

Source of funding
None.

Conflict of interest
None.