Single Case Reports
Benign Mesenchymoma of the Round Ligament
A Report of Two Cases with
Immunohistochemistry
MARGARET A. NUOVO, M.D., GERARD J. NUOVO, M.D., DANIEL SMITH, M.D., AND STEVEN H. LEWIS, M.D.
Benign mesenchymomas are tumors composed of an admixture
of two or more mature mesenchymal tissue types. Clinically and
histologically they are benign lesions. However, they are seldom
encapsulated and therefore may recur locally if incompletely excised. The authors report on two benign mesenchymomas composed of mature fat, thin-walled small and medium size vessels,
and spindle cells demonstrated to be smooth muscle by immunohistochemical studies. They were diagnosed in women in their
SOs. Both were located in the round ligament of the uterus. One
was discovered incidentally during hysterectomy, and the other
was unusually large, being diagnosed preoperatively as a retroperitoneal liposarcoma. Most round ligament tumors are leiomyomas orfibromas.To the authors' knowledge, this is the first
report of benign mesenchymomas occurring in this location. (Key
words: Benign mesenchymomas; Round ligament of uterus.) Am
J Clin Pathol 1990;93:421-424
THE BEST DESCRIPTIVE term for those tumors that
arise from mesenchymal tissue, differentiating into a varied assortment of tissue elements, and behave in a benign
fashion is "benign mesenchymomas," as first suggested
by Stout.16
The diagnosis of benign mesenchymoma is made when
at least two distinct mesenchymal elements are present
in the same tumor. The majority of benign mesenchymomas are composed of fat, blood vessels, and smooth
muscle. A mixture of different mesenchymal components
can be seen, giving rise to a spectrum of confusing nomenclature. However, angiomyolipoma is a term generally reserved for those lesions located in the kidney, associated with tuberous sclerosis in approximately 30-40%
of cases, and exhibiting thick-walled arterial vessels.
Histologically benign mesenchymomas can appear very
similar in composition to angiomyolipomas. 7 "
Received April 6, 1989; accepted for publication May 4, 1989.
Address reprint requests to Dr. Nuovo: Division of Ob/Gyn Pathology,
P&S Room 16-402, Columbia Presbyterian Medical Center, 630 West
168th Street, New York, New York 10032.
421
Departments of Pathology and Obstetrics and Gynecology,
The Cancer Research Center, Columbia University College of
Physicians and Surgeons, New York, New York
Benign mesenchymomas are a distinct entity and apparently not related to malignant mesenchymomas, which
display a malignant nature from the onset. However, they
may recur if inadequately excised, and they may be misdiagnosed in their clinical presentation because of their
apparent infiltrative nature.
The authors present two cases of benign mesenchymomas occurring at a previously unreported site, the
round ligament of the uterus. Both patients were in their
sixth decade, presenting with irregular vaginal bleeding
in Case 1 and increasing abdominal girth in Case 2. In
the former, leiomyomata uteri was the preoperative diagnosis, while in the latter a retroperitoneal liposarcoma
was suspected, based on diagnostic imaging studies. Both
tumors essentially were composed of mature adipose tissue
mixed with small and medium size vessels and spindle
cells proven to be of smooth muscle origin by immunohistochemistry.
Case 1
A 55-year-old woman presented with a chief complaint of irregular
vaginal bleeding and hot flashes for 1 year. Her past history was remarkable for a uterine curettage performed 3 months before admission
showing focal adenomatous hyperplasia of the endometrium. There was
a history of chronic hypertension, for which she received Inderal and
Aldomet.
Relevant physicalfindingsincluded moderate obesity and a 12-week
size uterus that appeared multinodular. Laboratory workup was normal.
A total abdominal hysterectomy and bilateral salpingo-oophorectomy
was performed with a preoperative diagnosis of symptomatic leiomyomata.
The uterus showed multiple leiomyomata that were subserosal, intramural, and submucosal in location. There was pressure atrophy of the
endometrium and no residual adenomatous hyperplasia. Additionally,
NUOVO ET AL.
422
A.J.C.P. • March 1990
a right round ligament mass was seen. It was well defined and measured
3.5 X 3 X 2 cm.
Microscopic examination of the round ligament mass showed a tumor
composed predominantly of mature adipose tissue admixed with many
small to medium size vessels displaying a thin wall, loosefibroustissue,
and frequent spindle cells with blunted nuclei resembling those of smooth
muscle fibers (Fig. \A). A trichrome Masson stain demonstrated the
eosinophilic cytoplasm of these spindle cells. The smooth muscle nature
of these cells was confirmed by desmin positivity (Fig. \B). A negative
Sioo immunostain excluded the possibility of a spindle cell lipoma or a
Schwann cell tumor.
The patient did well postoperatively, and there is no evidence of recurrence 8 months later.
Case 2
A 56-year-old woman presented with a chief complaint of chronically
swollen feet and increasing abdominal girth with weight gain over the
last few months. Her past history was relevant for pelvic inflammatory
disease treated with intravenous antibiotics 20 years ago and chronic
hypertension for which she received Lasix. Pertinent physical findings
included a large pelvic mass palpated at the level of the umbilicus, ascites,
and marked edema of lower extremities. Results of laboratory studies
were normal, as were the results of a barium enema. An abdominal and
pelvic computerized tomographic (CT) scan with contrast revealed a
large heterogeneous retroperitoneal soft tissue mass occupying much of
the abdomen and upper pelvis. It was not clearly separated from the
FIG. 2. A (upper). Computerized tomography with contrast showing
a large, well-defined soft-tissue mass occupying abdomen and pelvis,
with different areas of low density consistent with adipose tissue. B (center). A trichrome Masson stain highlights the cytoplasm of the spindle
cells as well as the vessel walls (X100). C (lower). Desmin positivity was
seen in the spindle cells (X400).
adnexa, uterus, or retroperitoneum and showed a well-defined enhancing
rim and several areas of low density consistent with adipose tissue (Fig.
2A). A retroperitoneal liposarcoma was suspected on the basis of these
findings.
A laparotomy with total abdominal hysterectomy and bilateral salpingo-oophorectomy was performed. The uterus contained multiple small
submucosal and intramural leiomyomata. There were multiple right
peritubal and left periovarian adhesions, and a left hydrosalpinx was
present. The right round ligament was distorted by a 25 X 22 X 19 cm
SINGLE CASE REPORTS
Vol. 93 • No. 3
mass that seemed to be contained by a dense capsule. The cut surface
was white-yellow and soft.
Histologically, there was abundant mature adipose tissue interspersed
with frequent acellular hyalinized areas. Also observed were multiple
small and medium-size vessels as well as spindle cells reminiscent of
smooth musclefibers.A trichrome Masson stain of these cells was consistent with smooth muscle (Fig. 2B). This was corroborated by immunohistochemical studies for desmin, which was positive (Fig. 2C). S10o
was negative focally in the spindle shaped cells, eliminating the possibility
of a Schwann cell origin.
The patient's postoperative course was uneventful, with no signs of
recurrence for 3 years.
Discussion
Ever since Stout's study of 39 mixed mesenchymal tumors in children,12 the term benign mesenchymoma was
used for those lesions composed of at least two differentiated mature or immature mesenchymal elements, excluding a fibrous constituent that is ubiquitous. Fat, blood
vessels, and smooth muscle were most commonly encountered, but other components such as myxomatous
tissue, skeletal muscle, bone, cartilage, and even hematopoietic elements also were occasionally described.
The origin of mesenchymomas from a primitive multipotential mesenchymal cell possessing the capability of
differentiating into diverse cell lines has been postulated.
The variability in appearance has created different diagnoses based on the predominant tissue or cell type, such
as angiomyolipoma, angiolipoma, angiofibroma, lipomyoma, etc. The most common locations were the kidneys,
perirenal structures, and extremities, but the lesion also
has been described in the mesentery, skin, ileum, liver,
ovary, mediastinum, retroperitoneal tissues, spinal cord,12
bone,1 seminal vesicles,10 and head and neck areas.2 Although the authors' cases also could be defined as angiomyolipoma, this term ordinarily is reserved for those
renal tumors that typically contain convoluted thickwalled blood vessels with little or no elastica.711 These
lesions are associated with tuberous sclerosis in about 3040% of cases. Extrarenal angiomyolipomas in close vicinity of the kidney or in totally unrelated sites such as liver,9
uterus,6 penis,3 vagina,14 anterior abdominal wall,4 and
Gerota's fascia15 also have been described, consistently
unassociated with tuberous sclerosis. 4 "
Benign mesenchymomas are more frequently found in
children and adolescents, being diagnosed less often after
the third decade of life. They usually are small, nonencapsulated, tend to merge with the surrounding structures,
and may recur if incompletely excised.
In both of the cases described, the tumors were encountered in the sixth decade of life. Such tumors generally
occur in the first three decades of life. The discovery of a
round ligament tumor was fortuitous in Case 1 because
it had been asymptomatic preoperatively; on the other
hand, in Case 2 a retroperitoneal malignant tumor such
423
as a liposarcoma was suspected clinically because of its
unusually large size and the CT observation of an adipose
tumor. Since benign mesenchymomas normally grow
slowly it is likely that the tumor in Case 2 had been present
for quite some time to attain a maximum diameter of 25
cm. It is not surprising, therefore, that a large component
of the tumor mass was formed by acellular hyalinized
areas.
Grossly both tumors seemed to be well encapsulated.
However, histologically in Case 1 the margins merged with
the smooth muscle, fibrous tissue, and large blood vessels
of the round ligament, covered by peritoneum. A pseudocapsule formed by long-standing compression of surrounding tissues was seen in Case 2, which probably explains its relative circumscription.
Notwithstanding the difference in size of both tumors,
their histologic resemblance was remarkable. Each displayed a predominance of mature adipose tissue in which
a prominent vascular constituent was evident, with focally
interspersed spindle cells displaying no particular orientation. This raised the differential diagnosis of spindle cell
lipoma in Case 1. In this entity, though, the spindle cells
tend to be aligned, and a vascular pattern usually is inconspicuous.7 Desmin immunoreactivity, Sioo negativity,
and characteristic trichrome Masson stains were useful in
confirming the smooth muscle nature of these cells and
in ruling out a spindle cell lipoma or a Schwann cell tumor. The vessels did not show a particularly thick wall
in either case.
The round ligament is embryologically homologous to
the male gubernaculum testis and therefore considered a
distinctly separate entity from the uterus. Tumors at this
site are rare. Various soft tissue tumors such as lipomas,
fibromas, leiomyomas, fibromyomas, schwannomas, and
sarcomas have been described occurring in the round ligament. 13 Of these, leiomyomas are the most commonly
found.5 Lesions termed lipoleiomyomas have been found
specifically in the uterus and broad ligament, and it has
been suggested that the frequency of partly lipomatous
lesions showing different combinations of mesenchymal
tissue differentiation at these sites may be higher than is
observed.8 The tumors reported in this latter study may
be benign mesenchymomas or angiomyolipomas, but no
illustrations were provided by the authors for evaluation.
The occurrence of immunohistochemically proven benign mesenchymomas in the round ligament, to the authors' knowledge, has not been heretofore described.
Acknowledgments. The authors thank Dr. Raffaele Lattes for his helpful
review and constructive discussion of the cases and Dr. Dan Friedman
for technical assistance.
References
1. Bugg El, Mathews RS. Benign mesenchymoma. South Med J
1970;63:268-273.
424
NUOVO ET AL.
2. Bures C, Barnes L. Benign mesenchymomas of the head and neck.
Arch Pathol Lab Med 1978;102:237-241.
3. Chaitin BA, Goldman RL, Linker DC Angiomyolipoma of the
penis. Urology 1984;23:305-306.
4. Chen KTK, Bauer V. Extrarenal angiomyolipoma. J Surg Oncol
1984;25:89-91.
5. Combes B, Ledoux A, Provendier B. Volumineux fibrome du ligament rond a developpement abdominal mais extraperitoneal. J
Gynecol Obstet Biol Reprod 1988;17:347-349.
6. Demopoulous RI, Denarvaez F, Kaji V. Benign mixed mesodermal
tumors of the uterus: A histogenetic study. Am J Clin Pathol
1973;60:377-383.
7. Enzinger FM, Weiss SW. Benign lipomatous tumors. In: Enzinger
FM, Weiss SW, eds. Soft tissue tumors. St Louis: C.V. Mosby
Company 1983:199-247.
8. Fernandez FA, Val-Bernal F, Garijo-Ayensa F. Mixed lipomas of
the uterus and the broad ligament. Appl Pathol 1989;7:70-71.
A.J.C.P. • March 1990
9. Goodman ZD, Ishak KG. Angiomyolipomas of the liver. Am J Surg
Pathol 1984;8:745-750.
10. Islam M. Benign mesenchymoma of seminal vesicles. Urology
1979;13:203-205.
11. Lattes R. Tumors of the soft tissues. Fascicle 1 in the Series: Atlas
of Tumor Pathology. Washington DC: Armed Forces Institute
of Pathology 1982; 101-104.
12. Le Ber MS, Stout AP. Benign mesenchymomas in children. Cancer
1962;15:598-605.
13. Mezzetti M. On tumors of the round ligament of the uterus (translated). Arch Ital Chir 1969;95:868-872.
14. Peh SC, Sivanesaratnam V. Angiomyolipoma of the vagina: An uncommon tumour. Case report. Br J Obstet Gynaecol 1988;95:
820-823.
15. Randazzo RF, Neustein P, Koyle MA. Spontaneous perinephric
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16. Stout AP. Mesenchymoma, the mixed tumor of mesenchymal derivatives. Ann Surg 1948;127:278-290.
Melanotic Schwannoma of Bone
Clinicopathologic, Immunohistochemical, and Ultrastructural Features
of a Rare Primary Bone Tumor
JEFFREY L. MYERS, M.D., WANDA BERNREUTER, M.D., AND WILLIAM DUNHAM, M.D.
The authors report a 35-year-old woman who presented with a
lytic and blastic tumor of the ilium with soft tissue extension.
The resected tumor showed light microscopic and ultrastructural
features characteristic of a melanotic schwannoma. An unusual
histologic finding was the presence of laminated concretions resembling psammoma bodies. Immunohistochemical stains for
S-100, HMB-45, and vimentin were strongly positive. The patient
is free of disease 18 months after complete surgical excision.
(Key words: Melanotic schwannoma; Nerve sheath tumors; Bone
neoplasms; Soft tissue neoplasms; Psammoma bodies) Am J
Clin Pathol 1990;93:424-429
INTRAOSSEOUS SCHWANNOMAS are rare, representing less than 1% of the primary benign bone tumors
reported by Dahlin and Unni. 3 Such tumors can occur at
virtually any age and affect both sexes with nearly equal
frequency.3,4'7 The most commonly involved site is the
mandible.3-4'7 Radiographically they appear as well circumscribed lytic lesions and often are associated with a
sclerotic border. Like their soft tissue counterparts, intraosseous schwannomas usually are solitary and behave
Received April 17, 1989; accepted for publication July 17, 1989.
Dr. Dunham's current address is Medical Center East, Birmingham,
Alabama.
Address reprint requests to Dr. Myers: Department of Laboratory
Medicine and Pathology, Mayo Clinic, Rochester, Minnesota 55905.
Division of Surgical Pathology, Department of Radiology, and
Division of Orthopedic Oncology, University of Alabama at
Birmingham, Birmingham, Alabama
in a benign fashion. Histologically they have features typical of schwannomas elsewhere and are composed of alternating Antoni A and B areas. Cellular Antoni A areas
predominate in some cases.4
Melanotic schwannomas, also referred to as melanocyte schwannomas, represent uncommon variants of
nerve sheath tumors that differ from typical schwannomas
in that they show light microscopic and ultrastructural
evidence of melanocyte differentiation. They affect males
and females equally and generally occur in young adults,
with a peak incidence in the third and fourth decades.5
They have been reported in a variety of visceral and soft
tissue sites but arise most commonly within spinal nerve
roots or sympathetic ganglia.5'1' Complete resection is curative in most patients. Metastases and death are rare and
have occurred only in patients with tumors of the sympathetic ganglia.5 The authors report a melanotic
schwannoma arising in bone that clinically and radiologically mimicked a malignant tumor.