 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.
Histogenesis:
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.
Clinical
presentation:
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.
Complete
obstruction of the abdominal aorta and renal arteries by a
large tumor embolus originating from the left ventricle
and aortic saddle embolism have even been
reported.
Image Link
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.
Myxomas
commonly give rise to signs of obstructed filling of the
left or right ventricle with subsequent dyspnea, recurrent
pulmonary edema, and
right heart failure.
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.
Site:
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).
Gross features:
Image
Link (WebPath)
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).
Microscopic features:
Image Link1
;
Image Link2
;
Image link3
;
Image link4 .
Microscopically it is extremely rare to find the tumour - free margins of
resection. Recurrence of the myxoma can be detected with
echocardiographic follow-up.
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).
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.
Visit:
Myxoid
Tumours of Soft Tissue
Note:
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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