Page 593 - Textbook of Pathology, 6th Edition

3. Abdominal pain 577
4. Attacks of dyspnoea due to bronchospasm
5. Right-sided heart failure due to involvement of tricuspid
and pulmonary valves and endocardium (page 451).
A number of secretory products in a functioning carcinoid
tumour have been demonstrated:
i) 5-Hydroxytryptamine (5-HT, serotonin)
ii) 5-Hydroxytryptophan
iii) 5-Hydroxy-indole acetic acid (5-HIAA)
iv) Histamine
v) Kallikrein
vi) Bradykinin
However, 5-HT and its degradation product, 5-HIAA, are
particularly significant in the production of carcinoid
Figure 20.36 Carcinoid tumour. Gross appearance at common
locations in longitudinal section. syndrome. 5-HT, a potent vasodilator and smooth muscle
stimulant, is normally synthesised in the endocrine cells of
the gut from dietary tryptophan. Tryptophan is first
appendiceal carcinoids commonly involve the tip of the hydroxylated to 5-hydroxytryptophan, then decarboxylated
organ and are solitary (Fig. 20.36). Cut section of all the to 5-HT and further oxidised to 5-HIAA by the monoamine
carcinoids is bright yellow. oxidase in the liver cells. It is then excreted in the urine. This
Histologically, the tumour cells may be arranged in a capacity to synthesise 5-HT and 5-HIAA is markedly elevated
variety of patterns—solid nests, sheets, cords, trabeculae in primary and hepatic metastatic carcinoids. Midgut
and clusters, all of which show characteristic palisading carcinoids have rich decarboxylating enzymes and are thus
of the peripheral cells. Acinar arrangement and rosettes able to produce large quantities of 5-HT and 5-HIAA,
are rarely seen. The tumour cells are classically small, accounting for high frequency of carcinoid syndrome in them.
monotonous, having uniform nuclei and poorly-defined Foregut and hindgut carcinoids, on the other hand, lack CHAPTER 20
cell boundaries (Fig. 20.37). The argentaffin carcinoids decarboxylating enzymes and, therefore, are less often
show eosinophilic granules in the cytoplasm which stain associated with carcinoid syndrome.
positively by the argentaffin reaction. Mitotic figures are
rare. However, the cytologic features are a poor guide for
distinguishing clinically benign from malignant behaviour APPENDIX
of the tumour, but all carcinoids infiltrate the bowel wall.
NORMAL STRUCTURE
CARCINOID SYNDROME. Carcinoid tumours that meta-
stasise, especially to the liver, are sometimes associated with Appendix is a vestigial organ which serves no useful purpose
the carcinoid syndrome. The syndrome consists of the in human beings but instead becomes the site of trouble at
following features: times. It is like a diverticulum of the caecum, usually lying The Gastrointestinal Tract
1. Intermittent attacks of flushing of the skin of face behind the caecum and varies in length from 4 to 20 cm
2. Episodes of watery diarrhoea (average 7 cm).

Figure 20.37 Microscopic appearance showing solid masses and trabeculae of uniform, monotonous, small cells with palisading of the peripheral
cells.