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Pathology of Cardiac Myxoma
Myxomas are the most common primary cardiac tumours.
A left atrial myxoma was first described in 1845.
Myxomas are neoplasms of endocardial origin.
The tumour usually projects from the endocardium into the cardiac chamber.
Cardiac myxomas originate from primitive, multipotential, mesenchymal cells, present in the heart-wall as embryonic remnants.
Immunohistochemical study supports this concept.
It also suggests that myxoma cells are derived from primitive subendocardial cells (not endothelial origin).
Some myxomas contain stellate cells resembling Schwann cells and cells with positive neuroendocrine markers, suggesting the view that myxomas originate from endocardial sensory nerve tissue.
Myxomas with gland like spaces contain mucus-secreting cells.
Immunohistochemical studies suggest that myxomas originate from cells having potential for both epithelial and mesenchymal differentiation.
On this basis myxomas are considered as hamartomas.
This is also supported by the study of proliferative and metastatic potential and expression of oncogene/tumor suppressor gene products.
Age and sex:
Myxomas occur in all age groups but are particularly frequent between the third and sixth decades of life.
Women predominate in most series.
Embolism occurs in a number of patients with myxomas.
Systemic embolism is particularly common as most myxomas are located in the left atrium.
The vessels affected include cerebral arteries, retinal arteries (transient or permanent visual loss may result) and in some cases renal, and coronary arteries.
The differential diagnosis of peripheral embolism should therefore include myxoma.
After surgical removal of the embolus, the diagnosis can often be made by histologic examination.
Constitutional disturbances, such as fatigue, fever, erythematous rash, arthralgia, myalgia, and weight loss, and laboratory abnormalities, such as anemia and elevations in the erythrocyte sedimentation rate and the serum C-reactive protein and globulin levels, have been observed in many patients.
Cardiac myxomas usually develop in the atria. About 75 percent originate in the left atrium, and 15 to 20 percent in the right atrium.
Most tumours (90%) arise in the atrial septum in the region of fossa ovale, but they can also originate, in descending order of frequency, from the posterior atrial wall, the anterior atrial wall, and the atrial appendage.
Ventricular location is rare.
There have also been reports of combined atrial and ventricular tumours and biventricular tumours.
Myxomas of the heart valves are rare.
Myxomas usually occur sporadically, but familial myxomas have been reported.
Multiple myxomas are uncommon but multiple lesions in more than one cardiac chamber may occur in familial myxoma.
Myxoma originating from heart valves:
The origin of true myxomas in cardiac valves was disputed. Recently transesophageal echocardiography has been advocated to differentiate it from a papillary fibroelastoma . Review of the world literature concluded that true myxomas may originate from a heart valve, commonly in the right than left and may be attached to the atrial or ventricular side of the atrioventricular valve leaflets.
The Myxoma syndrome: (Carney's Complex).
Also known as Familial Endocrine Myxolentiginosis.
In familial myxomas, there is an autosomal dominant mode of inheritence with a variable phenotype.
The syndrome consists of variable complex disorders mentioned below (all may not be present in one patient):
i) cardiac myxomas (usually multiple)
ii) cutaneous myxomas (single or multiple)
iii) mammary myxoid fibroadenomas (single or multiple)
iv) spotty mucocutaneous pigmentation (including lentigines and blue nevi and combinations)
v) psammomatous melanotic schwannomas,
vi) primary pigmented nodular adrenocortical disease (including patients symptomatic with Cushing syndrome),
vii) testicular tumours (bilateral, multicentric Sertoli cell tumours)
viii) pituitary growth-hormone secreting tumours (causing acromegaly or gigantism).
These are usually single, 1 to 10 cm in diameter and are sessile, pedunculated or papillary type.
Some are globular with smooth surface and may show surface thrombus.
They are gray to dark red in colour, soft and friable with spotty hemorrhage.
Cut surface is gelatinous and in part almost mucoid.
Some may be firm and occasional gross calcification is seen even to the extent of converting the entire tumour in to a calcified mass (petrified cardiac myxoma).
Characteristic microscopic appearance is a myxomatous matrix containing stellate or myxoma cells.
Absence of mitotic figures is of special importance.
Myxoma cells are fusiform, polyhedral or stellate with elongated, round or oval nuclei and are arranged in single or multiple layers surrounding vascular channels.
Occasionally, myxoma cells may be arranged in small nests, singularly or dispersed throughout the myxoid stroma.
Multinucleated myxoma cells are composed of small groups of closely apposed cells with single nuclei.
Apart from myxoma cells, other cell types seen in myxoma are endothelial cells, smooth muscle cells and myofibroblasts (may be due to differentiation).
Microscopically it is extremely rare to find the tumour free margins of resection.
Recurrence of the myxoma can be detected with echocardiographic follow-up
Immunohistochemistry clearly indicates differences of the various cell types observed in myxoma.
Other cell types observed in myxoma are lymphocytes, plasma cells, macrophages, and mast cells.
Foci of extramedullary hematopoiesis are seen occasionally.
For diagnosis overall picture is more important than high-power observation of cell characters and absence of mitosis is important in the diagnosis of myxoma.
1. Recurrence and "malignant" cardiac myxomas:
Recurrence after surgical excision is rare. Recurrence is explained as:
1. Incomplete excision with subsequent regrowth.
2. Malignant nature of the tumour
3. Familial with multicentric onset (myxoma syndrome).
Review of world literature concludes that all intracardiac tumours with metastases are myxoid variety of soft tissue sarcomas (not myxoma).
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