Appendix

Contributed by Bella Lingjia Liu, M.D.

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Contributed by Bella Lingjia Liu, M.D.

• Nonmucinous adenocarcinoma (J Pathol Transl Med 2021;55:247)
  • Resembles colorectal adenocarcinoma
    • Neoplastic glands with columnar cells containing hyperchromatic nuclei; often cribriform and with necrotic debris
  • 2 tiered grading system based on gland formation (WHO 5th edition)
    • Low grade (well to moderately differentiated): ≥ 50% gland formation
    • High grade (poorly differentiated): < 50% gland formation
• Mucinous adenocarcinoma (Mod Pathol 2017;30:1177)
  • Similar to those of the colon and rectum; requires > 50% extracellular mucin
    • Irregular and jagged glands infiltrating the appendiceal wall or floating in the mucin; arranged as single cells, strips, clusters or complex glandular structures
    • Often with high grade cytology
  • 3 tiered grading system (AJCC 8th Cancer Staging Manual) (Mod Pathol 2014;27:1521, J Pathol Transl Med 2021;55:247, Adv Anat Pathol 2018;25:38)
    • G1 (well differentiated): only applies to low grade mucinous neoplasm
    • G2 (moderately differentiated): conventional mucinous adenocarcinoma without signet ring cell component
    • G3 (poorly differentiated): high grade mucinous adenocarcinoma with signet ring cells component (< 50%)
  • May rupture with transcoelomic spread to the peritoneum or ovaries
• Signet ring adenocarcinoma (J Pathol Transl Med 2021;55:247)
  • Similar to signet ring cell adenocarcinoma elsewhere in the GI tract; requires > 50% signet ring cells

Contributed by Bella Lingjia Liu, M.D.

A 58 year old patient presents with acute right lower quadrant abdominal pain and is found to have an appendiceal mass during surgery. Histological examination of the resected specimen reveals a lesion as depicted in the images above. Which of the following is the correct diagnosis?

1. High grade appendiceal mucinous neoplasm
2. Low grade appendiceal mucinous neoplasm
3. Mucinous appendiceal adenocarcinoma
4. Signet ring cell adenocarcinoma

C. Mucinous appendiceal adenocarcinoma. The tumor demonstrates infiltrative growth pattern with irregular glands and large mucin pools, adjacent to a low grade mucinous neoplasm. Answers A and B are incorrect because both low grade appendiceal mucinous neoplasm and high grade appendiceal mucinous neoplasm exhibit a pushing type of invasion, unlike the irregular infiltrative pattern seen here. Answer D is incorrect because signet ring cell adenocarcinoma should typically have a minimum of 50% of neoplastic cells displaying signet ring cell morphology.

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Reference: Appendix - Adenocarcinoma

You are reviewing a case of acute appendicitis and notice the findings in the images provided. Which of the following statements is true regarding this lesion?

1. It is characterized by frequent microsatellite instability
2. It is frequently positive for CK7 and negative for CK20
3. It usually involves patients 30 - 50 years of age
4. Signet ring cell type is associated with a worse prognosis

D. Signet ring cell type is associated with a worse prognosis. The clinical and histological findings suggest appendiceal signet ring cell adenocarcinoma, which is associated with a worse prognosis compared to other types of appendiceal adenocarcinoma. Answer A is incorrect because appendiceal adenocarcinoma typically displays a low prevalence of microsatellite instability. Answer B is incorrect because appendiceal adenocarcinoma stains positive for CK20 but majority lacks CK7 expression. Answer C is incorrect because appendiceal adenocarcinomas usually occur in patients in their fifth to seventh decade of life.

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Reference: Appendix - Adenocarcinoma