Carcinoid Syndrome – A Paraneoplastic Syndrome

00:02 Moving on, carcinoid syndrome.

00:04 And this is due largely to the elaboration by the carcinoid tumor of serotonin, which causes effects at a distance.

00:14 Carcinoid tumor are most common in the GI tract but you can have ovarian carcinoid, you can have primary pulmonary carcinoids, you can have others, but the most common ones are going to be in the GI tract, particularly in the small bowel.

00:30 And what we're showing here with the green arrow on the left hand side is a segment of proximal jejunum and in it is a kind of a single nodular mass that we've incised multiple times.

00:43 It wasn't cut in nature, that's the pathologist.

00:47 And then when we look at it histologically, it is a monomorphous population of small round blue cells with granular cytoplasm.

00:54 These guys are making a variety of small molecular weight hormones and include the production of serotonin.

01:03 Now, in general, even if that tumor which is usually a fairly indolent tumor is considered a malignant tumor, but it's indolent, grows slowly, if even if that tumor is making its serotonin and other molecules that it's going to release, the liver metabolizes that, so we have no effect.

01:23 However, once the tumor metabolizes to the liver, and we replace a significant chunk of the liver with the tumor, as we see here on this slide, on the left hand side is the mass, metastatic carcinoid, on the right, are the nests of the carcinoid cells within the liver.

01:43 At that point, now the liver can't metabolize all the serotonin that's being released.

01:48 And now we're going to get systemic effects due to the serotonin washing over endothelium, upstream, or downstream.

01:58 So from that liver metastasis, not being able to completely metabolize old serotonin, we're releasing it into the vasculature into the hepatic vein into the inferior vena cava into the heart.

02:11 And the first kind of the tissue that's going to be affected by this are going to be the valvular tissues.

02:18 So in carcinoid syndrome, there can be other manifestations but here for example, we're going to be talking about what happens to the valves.

02:26 In this patient, there was a significant tumor burden within the liver, significant serotonin levels washing over the valves.

02:36 The tricuspid valve on the right is thickened because of an intimal hyperplasia due to smooth muscle proliferation and matrix synthesis.

02:44 And that valve has become somewhat incompetent as a result of that.

02:49 So the valve has been thickened and we get tricuspid insufficiency.

02:54 The mitral valve, however, is completely unaffected.

02:56 That's a completely normal valve on the left hand side.

02:59 That's because now as these 'evil humors' as we refer to them, the serotonin goes through the lung, the lung endothelium is able to metabolize it.

03:09 So the the left sided valves in a patient with metastatic carcinoid involving the liver are not involved.

03:16 It's the right side of valves that are seeing this first and we will get this thickening due to smooth muscle proliferation of intimal hyperplasia.

03:25 Well, that also means that, Gee the pulmonic valve must also be involved and yes it is.

03:30 So you can see that the aortic valve valve in this patient completely normal on the left hand side.

03:34 The pulmonic valve in comparison is markedly thickened and stiff, so that we will have a degree of pulmonic stenosis.

03:43 So classic carcinoid syndrome involving the heart, carcinoid heart disease due to serotonin release is going to cause tricuspid insufficiency and pulmonic stenosis in severe cases.