Appendix

Question 1

Describe the anatomy of the appendix

Answer 1

Macro: 5-10cm long tubular structure representing a true diverticulum
Base located at convergence of taenia coli
Micro: neuroendocrine and lymphoid cells
Embryo: caecal diverticulum at 6 weeks, medial rotation, pushed down into RLQ by caecum
Blood supply: appendiceal a, terminal branch of SMA
Lymph: a single intermediate node
Nerves: superior mesenteric plexus efferents, sensory to T10 dermatome

Question 2

What is a mucocoele?

Answer 2

A degenerative obstructive change in the appendix resulting in dilation and mucin production
It is not neoplastic
It can cause mucin accumulation in the abdominal cavity
- no malignancy but long-term compressive symptoms

Treatment: appendicectomy and confirmation of diagnosis
Intra-op: take photos as per the peritoneal cancer index

Question 3

What is a low-grade appendix mucinous neoplasm (LAMN)?

Answer 3

A dysplastic mucin-producing lesion of the appendix
Histo: uniform basally-oriented nuclei with little to no mitotic activity, abundant mucin
It is not neoplastic but 1/3 of ruptured LAMN can develop pseudomyxoma peritonei
Stage: Tis, T3, T4 (a pushing of tumour against borders rather than infiltration)

Treat: appendicecomy and confirmation of diagnosis
Intra-op: take photos as per peritoneal cancer index; refer if ruptured

Question 4

What is a high-grade appendiceal mucinous neoplasm (HAMN)?

Answer 4

A dysplastic mucin-producing lesion of the appendix with increased cellular atypia
Histo: enlarged hyperchromatic nuclei, loss of polarity, cribiform growth, increased mitoses
Stage: Tis, T3, T4

Treat: appendicectomy and confirmation of diagnosis
Intra-op: take photos as per the peritoneal cancer index; refer if ruptured

Question 5

Are LAMN and HAMN infiltrative?

Answer 5

LAMN and HAMN do not infiltrate but may push and thin the appendix wall until it ruptures, then cause mucin spread within abdomen and PMP

Question 6

What is mucinous appendiceal adenocarcinoma?

Answer 6

A neoplastic lesion of the appendix with infiltrative capability
Histo: >50% tumour mass is extracellular mucin; desmoplastic stromal reaction
Grade: well, moderately and poorly differentiated with signet cells
G1 tumours more likely to produce PMP.
G3 tumours more likely to metastasise distantly and cause carcinomatosis

Question 7

What is pseudomyxoma peritonei?

Answer 7

A clinical syndrome of diffuse mucinous peritoneal involvement, usually in association with a ruptured mucinous appendiceal lesion (mucocele or LAMN)

The mucin is benign but eventual obstruction and death

If the mucin contains cells with the architectural features of carcinoma, it is peritoneal mucinous carcinomatosis