2007, Volume 23, Number 3, Page(s) 160-163
Primary renal myxoma: A case report
Filiz BOLAT1, Tahsin TURUNÇ2, Fazilet KAYASELÇUK1, Şerife ULUSAN3, Nebil BAL1
1Başkent University Faculty of Medicine, Department of Pathology, ANKARA
2Başkent University Faculty of Medicine, Department of Pathology, ANKARA
3Başkent University Faculty of Medicine, Department of Radiology, ANKARA
Keywords: Kidney, myxoma
Myxomas are uncommon soft-tissue neoplasms, which are extremely rare in the kidney with ten cases reported in the literature.
A 27-year-old woman was admitted to our hospital with epigastric pain and pelvic mass. Magnetic resonance imaging (MRI) of the abdomen showed a well defined 15x14x7 cm tumoral mass in the left kidney. The patient underwent a left-sided nephrectomy. On microscopic examination, the tumor consisted of large amounts of myxoid material containing a few uniformly scattered spindle cells. Immunohistochemically, tumor cells stained positive for vimentin, but not for S-100 protein, epithelial membrane antigen, pancytokeratin and smooth- muscle actin. With these histopathological and immunohistochemical findings, the case was diagnosed as ‘renal myxoma’.
In this report, the clinical and histopathological findings, differential diagnosis and possible histogenesis of a case of myxoma that was originated from the left kidney of a 27 year-old female patient is presented.
Myxomas may occur in a variety of tissues
but are most common in skeletal muscle and
generally follow an indolent course. Ten cases
of kidney myxomas have been reported in the literature1-5
. The histogenesis of myxoma is
still debated. Cardiac myxomas are thought to
derive from multipotential mesenchymal cells,
whereas their soft tissue counterpart is thought to originate from the primitive mesenchymal
cells with fibroblastic features1,3,4,6
The differential diagnosis of myxoid tumors
of the kidney includes many other benign
and malignant soft-tissue lesions that exhibit
prominent secondary myxoid features. It is important
to recognize the existence of a renal
myxoma to avoid confusing it with the malignant
neoplasms having secondary myxoid features
that may involve the kidney1,3,4,6.
In this paper, the morphologic characteristics
of this tumor are compared with other
myxoid lesions of the kidney, which might
cause confusion in differential diagnosis.
A 27-year-old woman was admitted to our
hospital with epigastric pain and pelvic mass incidentally
diagnosed by ultrasonography during
annual medical check-ups. The results of her
physical examination were unremarkable, and
laboratory values were within normal limits.
Magnetic resonance imaging (MRI) of the abdomen
demonstrated a well defined semisolid /semicystic
mass occupying the lower calyces of
the left kidney (Figure 1
). On the MRI, the tumor
was depicted as a homogeneous low-signal
intensity on the T1 and heterogeneous high signal
intensity on the T2-weighted pulse sequences.
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|Figure 1: Magnetic resonance images demonstrate a tumor
with heterogeneous high-signal intensity on the T2 - weighted
pulse sequence (arrows).
The patient underwent a left-sided nephrectomy.
The nephrectomy specimen weighed
14 gr excepting the perirenal fat. On serial sections,
the lower pole of the left kidney demonstrated
a 15x14x7 cm tumor surrounded by a
thick, pearly white capsule which separated it
from the adjacent renal parenchyma. The surface
of the gray-white mass had a semitranslucent
appearance and the mass was composed of a gelatinous,
stringly mucoid material (Figure 2).
No calculi were identified within the renal pelvis
or proximal ureter. The surrounding kidney
parenchyma appeared grossly unremarkable.
Click Here to Zoom
|Figure 2: The middle pole of the left kidney contains a well-demarcated,
yellowish, and gelatinous tumor compressing the
surrounding renal parenchyma (arrows).
Histopathologic examination revealed a
paucicellular and hypovascular tumor consisting
of large amounts of basophilic interstitial mucoid
material containing sparse slender, spindle,
oval and stellate cells (Figure 3), and occasional
fine strands of fibrous tissue. The myxoid material
stained positively with Alcian blue. Nucleoli
and mitotic figures were not evident.
Click Here to Zoom
|Figure 3: A fibrous pseudocapsule separates the sparsely cellular
myxoid tissue from the renal parenchyma (arrows) (HE
x100). Inset: Tumor showing spindled to polygonal cells in
abundant myxoid stroma (HE x200).
No lipoblast, giant cells, or other spindle
cell components were identified. The tissue at
the interface between the myxoid stroma and the
renal parenchyma showed thin bands of fibrous
tissue forming a pseudocapsule. No obvious infiltration
into the parenchyma was seen.
Immunohistochemically, tumor cells were
stained positively with vimentin, while S100 protein, epithelial membrane antigen (EMA),
pancytokeratin and smooth-muscle actin (SMA)
did not show any positive reaction. With the
above mentioned gross, microscopic and immunohistochemical
findings, the final histopathological
diagnosis was myxoma of the kidney.
The patient is free of disease for one year.
Myxomas were originally described by
Virchow in 18637,
the basic histologic criteria for diagnosis in
1948. Enzinger, in 1965, suggested that the lack
of aggressive growth and the paucity of vascular
structures suggested a similarity to fibroblasts
and a close relationship to the early developmental
stage of ganglia9
The histogenesis of renal myxoma remains
unresolved and speculative. Some authors have
considered it to be a degenerative change seen
in adipose tissue in brown atrophy of the heart
or similar to the myxoid changes in uterine leiomyomas.
The others believe that the uniform
cellular component throughout the lesion supports
a neoplastic nature rather than a regressive
change within a preexisting tumor. The cellular
origins of the tumor have been contemplated to
be primitive mesenchymal cells with fibroblast
Myxomas can be located in skin, soft tissues,
bone, juxta-articular space, sinonasal cavity,
maxillary antrum, and in various organs or
viscera10. Myxomas may be observed in eye11, heart12, ovary13, and kidney1-5.
Between 1887 and 1995 nine case reports
of renal myxoma were published. Melamed et
al. reviewed these nine cases, and assumed that
only three of them were pure renal myxomas
(incl. their two cases)1. There have been two
additional case reports on this entity within the
last year4,5. Our case might be the sixth case
of pure renal myxoma.
Intrarenal myxomas have no gender predilection.
Patients’ ages range from 36-68 years (mean 54.5 years). The lesions are found more
commonly within renal poles and they vary in
size from 4 to 28 cm (mean 12.2 cm)6. They
have a smooth capsule and a solid-cystic cut
surface. This appearance is not specific for the
renal myxoma. Histologic features are distinctive,
and our case resembles to the other renal
myxomas that were previously described in the
Renal myxoma is a very rare tumor composed
of fibroblast-like spindle cells and abundant
myxoid stroma. It is essential to distinguish
renal myxoma from malignant and benign mesenchymal
tumors exhibiting prominent secondary
myxoid features. The spectrum embraces
perineurioma, myxoid neurofibroma, myxoid
leiomyoma, myxolipoma, low grade fibromyxoid
sarcoma, the myxoid variants of malignant
fibrous histiocytoma (low grade myxofibrosarcoma),
liposarcoma, leiomyosarcoma, rhabdomyosarcoma,
and extraskeletal chondrosarcoma.
Grossly, all these neoplasms have a variable
gelatinous consistency. However, each tumor
has a complete set of exclusive morphologic, ultrastructural,
immunophenotypic, and genotyphic
features. In the particular case of renal sarcomas,
increased cellularity, pleomorphism, mitoses,
well-developed vascularity, and necrosis
are usually apparent1,4,6.
Myxoid stroma has also been found in sarcomatoid
renal cell carcinoma, as well as in the
sarcomatoid variant of transitional cell carcinoma14,15. These changes are usually focal,
and an appropriate sampling will demonstrate
adjacent anaplastic spindle cells together with
areas of epithelial differentiation.
Renomedullary interstitial cell tumors are
the commonest benign mesencyhmal lesions of
the kidney16. Occasionally they may be highly
myxoid but usually have a dense fibrous stroma
with areas of hyalinization. Rarely do they
grow to large size, however, because of their
uniform cell population they are considered neoplasms
rather than hamartomas1.
In conclusion, we have described an unusual case of renal myxoma. It is important to
distinguish this benign tumor from many other
highly malignant neoplasms that may involve
the kidney and exhibit secondary myxoid features.
Myxomas have an excellent clinical outcome
after radical excision and their recognition is
essential to avoid an overtreatment .
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