Abdominal cavity myolipoma presenting as an enlarging incisional hernia
Citation: Moore MO, Richardson ML, Rubin BP, Baird GS. Abdominal cavity myolipoma presenting as an enlarging incisional hernia. Radiology Case Reports, [Online] 2006;1:5.
Copyright: © Michael L. Richardson. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs 2.5 License, which permits unrestricted reproduction and distribution, provided the original work is properly cited. Commercial use and derivative works are not permitted.
Abbreviations: CT, computed tomography, MRI, magnetic resonance imaging, 3D, three dimensional, MB, megabyte, STIR, short tau inversion recovery.
Mark O. Moore is in the School of Medicine, University of
Washington School of Medicine, Seattle, Washington, United States of America.
Michael L. Richardson is in the Department of Radiology, University of Washington
School of Medicine, Seattle, Washington, United States of America. E-mail:
mrich@u.washington.edu
Brian P. Rubin and Geoffrey S. Baird are in the Department of Anatomic Pathology,
University of Washington School of Medicine, Seattle, Washington, United States
of America.
Competing Interests: The authors declare that no competing interests exist.
Published: January 27, 2006
DOI: 10.2484/rcr.v1i1.5
We present a case of an abdominal cavity myolipoma which herniated through a low transverse abdominal (Pfannenstiel) incision, and presented as an enlarging abdominal wall mass. Magnetic resonance imaging (MRI) prior to surgery demonstrated an encapsulated solid tumor mass demonstrating fat signal and and increased T2-weighted signal. Postsurgical histological tissue diagnosis was myolipoma. Recognition of the intra- and extraperitoneal location of this abdominal tumor was essential for accurate surgical planning.
Introduction
Myolipoma is a benign soft tissue neoplasm composed of a mixture of smooth
muscle and mature adipose tissue (1, 2). It is a rare lesion that can occur
at many anatomical locations, including the spinal cord (3), retroperitoneum
(4-6), abdominal cavity (6), uterus and adnexae (7-11), eyelid (12), pericardium
(13), and breast (14). To our knowledge, a case of myolipoma within an incisional
hernia has not previously been described in the literature. We report such
a case, and review the computed tomography, magnetic resonance imaging and
histological findings of myolipoma.
Case Report
A 55-year old woman presented to our institution with a 6-month history of
progressively enlarging abdominal mass with concomitant right lower quadrant
discomfort and right leg pain.
One year prior to this admission, a 6 cm right adnexal mass had been noted
on pelvic exam as part of a preoperative workup for symptomatic cholelithiasis
at another institution. Computed tomography (CT) exam at that time demonstrated
a fibrotic-appearing 7 cm mass around a 2 cm ovary. This mass extended anteriorly
to the posterior margin of the right abdominal musculature (Figure 1).
Figure 1. Initial CT examination, demonstrating
a mass (M)
posterior to the right abdominal wall. [PowerPoint
Slide]
She underwent and uncomplicated laparoscopic cholecystectomy, with concomitant
excisional biopsy of the right adnexal mass and right ovary through a preexisting
Pfannenstiel incision. Initial pathology was consistent with benign scar tissue
and inflammatory adhesions.
The next few months were marked by worsening right leg pain, which had been
present prior to initial removal of the mass. She characterized this pain as
a deep nagging pain, starting in her right buttock and radiating down to her
right groin and the lateral side of her right thigh. In addition to this pain,
she reported worsening gastrointestinal symptoms over the same time period,
including nausea, constipation, and a sensation of postprandial fullness that
required her to stand in order to finish eating a meal. She also noted that
she could feel the mass again, and felt that it had begun to enlarge. On physical
examination, a large firm mass was palpated in the right lower abdominal wall
in the region underlying the Pfannenstiel incision. Laboratory studies were
within normal limits.
Repeat CT scan of the pelvis (Figures 2 and 3) now demonstrated a 9.4 x 2.3
cm dumbbell-shaped right lower quadrant mass in contact with the psoas muscle,
and extending through the abdominal wall into the overlying subcutaneous tissue.
It was shown to abut the right iliac wing, external iliac vessels, and urinary
bladder. No calcifications were noted within the mass.
Figure 2. Repeat CT scan, showing a dumbbell-shaped right lower quadrant mass (M) in contact with the psoas muscle, extending through the abdominal wall into the overlying subcutaneous tissue. [PowerPoint Slide]
Figure 3. 3D reconstruction of
lower abdomen from repeat CT scan data, showing mass (M) protruding through
abdominal wall.
A. Left anterior oblique view from a horizontally rotating
3D movie (QuickTime, 9.4 MB)
shows the mass, as well as the subcutaneous scar from the prior Pfannenstiel
incision site (P).
B. Cephalically angled view from a vertically
rotating 3D movie (QuickTime, 11.5 MB)
showing mass (M), subcutaneous scar (arrows) and anterior abdominal wall
scar (arrowheads) from prior Pfannenstiel incision site. [PowerPoint
Slide]
Magnetic resonance imaging (MRI) of the pelvis (Figure 4) demonstrated
a large extraperitoneal mass occupying the right hemi-pelvis, extending
through the
abdominal wall musculature at the lateral aspect of the prior Pfannenstiel
incision.
Figure 4. Axial T1-weighted image
of lower abdomen, showing dumbbell-shaped right lower quadrant mass adjacent
to the psoas muscle, extending through the abdominal wall into the overlying
subcutaneous tissue. [PowerPoint
Slide]
The small bowel and cecum were compressed by the mass, and the urinary
bladder was displaced medially. A thin well-demarcated capsule surrounding
the lesion
demonstrated increased signal intensity on short-tau inversion recovery
(STIR) and decreased signal intensity on T1-weighted MRI (Figure 5).
Figure 5. Coronal T1-weighted
(A) and STIR (B) images of anterior abdomen, demonstrating mass (M) herniating
through anterior abdominal wall at the lateral margin of the Pfannenstiel
incision (arrows). [PowerPoint
Slide]
The interior of the lesion revealed a mixture of fat signal and increased
T2-weighted signal. Also noted was an additional tissue component that
was of increased
signal intensity on STIR-weighted imaging and heterogeneous on T1-weighted
imaging, either hypodense to muscle or isodense to it. Liposarcoma, malignant
fibrous histiocytoma, desmoid tumor, and leiomyosarcoma were considered
in the differential diagnosis prior to surgery.
Surgical total excision was performed for symptomatic relief. At operation,
the tumor was found to herniate through the lateral aspect of the
patient’s
prior Pfannenstiel incision in the right lower quadrant of the abdominal
wall. With further investigation, it became apparent that the neoplastic
process
extended into the peritoneal cavity, which was subsequently explored.
A mobile mass with loose fibrinous attachments to the intraperitoneal
abdominal
wall
and loops of small bowel was present.
The pathologic specimen had a maximal diameter of 16 cm (Figure 6).
Macroscopic examination showed a pink, multi-lobulated soft tissue
mass, with a glistening,
membranous capsule covering the entire exterior surface.
Figure 6. Gross photograph of
the excised mass shows a large, lobulated lesion surrounded by a thin, well-vascularized
and fibrous pseudocapsule. [PowerPoint
Slide]
Numerous fine blood vessels coursed over the surface of the mass, emanating
from a vascular pedicle. On fresh cut section, the tissue was homogeneous
and pale yellow in color, and a 3.0 cm fluid-filled cyst was present
in the center
of the mass.
On histologic examination (Figures 7 and 8), the mass was composed
of fascicles of benign appearing spindle cells admixed with mature
adipose
tissue. The
spindle cells had elongated nuclei with tapering ends and brightly
eosinophilic cytoplasm.
Figure 7. Photomicrographs of
the tumor with hematoxylin and eosin stain.
A. Low power photomicrograph of the tumor showing an admixture
of mature adipose tissue and benign-appearing spindle cells with brightly
eosinophilic cytoplasm. [PowerPoint
Slide]
Figure 7. Photomicrographs of the tumor
with hematoxylin and eosin stain.
B. High power photomicrograph showing cytologic features
of spindle cell proliferation. These spindle cells have elongated nuclei
with tapered ends and abundant eosinophilic
cytoplasm. [PowerPoint
Slide]
Figure 8. High-power
microscopic section of the tumor with immunohistochemical stain for desmin.
The brown areas shown here denote lesional cells which are diffusely and
strongly positive for desmin. Similar lesional cells were also diffusely
and strongly positive for smooth muscle actin (not shown). [PowerPoint
Slide]
Cytologic pleomorphism, mitotic figures and necrosis were not identified.
On immunohistochemical studies (Figure 8), spindle cells were diffusely
and strongly
positive for smooth muscle actin and desmin.
All 20 cells examined contained a balanced translocation between
chromosomes 12 and 14 [46, XX, t(12,14)(q15;q23)], and 5 of these
cells contained
multiple additional abnormalities. Final histological diagnosis
was compatible with
myolipoma.
The patient made an uneventful recovery and was discharged from
the hospital 6 days after surgery. At 2 weeks postoperative follow-up
she was symptom-free.
Discussion
Myolipoma is an exceedingly rare but benign soft tissue tumor that is composed
of smooth muscle cells and adipocytes (1, 2). It may occur in many anatomic
sites throughout the body including spinal cord (3), retroperitoneum (4-6),
abdominal cavity (6), uterus and adnexae (7-11), eyelid (12), pericardium (13),
and breast (14). The majority of lesions arise in the deeply located soft tissues
of the retroperitoneum and abdomen where prompt clinical detection is difficult.
Consequently, they are usually large at initial presentation with a greatest
diameter of more than 10 cm (2). Complete surgical resection of a myolipoma
is considered to be curative, with no known reports or local recurrence, metastatic
disease or malignant transformation (2).
The gross pathologic appearance of myolipoma is that of a completely or partially
encapsulated soft tissue mass. Histologically, it is composed of bundles and
sheaths of smooth muscle interspersed with islands of mature adipose tissue.
The tissue components may be present in varying proportions, but there is typically
a regular distribution of adipose tissue mixed throughout the lesion. In our
case, the tumor exhibited the distinct microscopic appearance of myolipoma,
with bland, well-differentiated smooth muscle and adipose tissue. Both of these
components lacked any features suggestive of malignancy, such as cytologic
atypia, mitotic figures, or necrosis. The immunohistochemical appearance in
our case was characteristic as well, with smooth muscle elements that were
strongly positive for smooth muscle actin and desmin.
Radiologic features reflect the dual tissue composition revealed at pathologic
examination. The CT and MRI imaging appearances therefore vary along a spectrum,
representing varying proportions of intermixed adipose tissue and smooth muscle
components. On CT, both fat and soft-tissue attenuation areas are noted.
On T1-weighted MRI imaging, smooth muscle elements appear as
areas of intermediate signal intensity. T2-weighted images of
these regions are of intermediate to
high signal intensity. Calcifications are variably present, though
they more commonly occur in large-sized lesions. Our patient’s
lesion did not exhibit evidence of calcification by CT or MRI,
but was otherwise typical for myolipoma.
Incisional hernias generally present as a bulge in the abdominal wall in the
area of a prior surgical incision. This is a relatively common occurrence following
midline abdominal operations, with a reported prevalence of at least 10% of
patients undergoing these procedures (15, 16). Incisional hernias are much
less likely following a Pfannenstiel incision, with a reported prevalence of
2.1% in one large series (15). Though the type of incision utilized is important,
there are also a variety of predisposing biological and mechanical factors
that play a role in hernia development. Constitutional variables including
diabetes, obesity, malnutrition, and metabolic or lung disease (16, 17), as
well as technical variables such as suture material and wound closure technique
(16) may impair the normal healing response and are therefore thought to be
important risk factors.
Only a few instances have been described of intraabdominal tumors protruding
into an incisional hernia of the anterior abdominal wall. Delpero et al. (18)
reported a case of primary fibrosarcoma of the peritoneum presenting as a huge
pedunculated abdominal mass protruding into a large incisional hernia of the
anterior abdominal wall in an elderly female patient. Marshall et al. (19)
reported an enlarging incisional hernia of the lower abdomen attributable to
benign cystic mesothelioma of the peritoneum. They noted a tendency for this
tumor to recur locally, with diffuse multicystic involvement of the abdominal
and pelvic peritoneal surfaces. Sataloff et al. (20) reported a case of abdominal
wall scar endometriosis that presented as a tender lump beneath the site of
a prior cesarean section. Huber-Bucholz et al. (21) documented the occurrence
of metastatic Fallopian tube carcinoma in an incisional hernia 15 years after
initial surgical intervention.
Of these four cases, three involve agressive tumors with an inherent capacity
for recurrence or metastasis. The case of scar endometriosis is an exception,
since it does not represent invasion by an uncontrolled neoplastic process.
Instead, it is explained by direct intraoperative transfer of endometrial cells
or peritoneal metaplasia (20). However, the tendency for spread of endometrial
implants to extrapelvic sites, especially following surgical procedures, has
been well-documented. The case we describe here differs from these prior reports
in that it involves a characteristically non-aggressive disorder that is not
known to recur following excision.
Although myolipoma frequently originates in the abdominal cavity,
we are unaware of one presenting as an enlarging incisional hernia.
This unusual behavior
raises the possibility that the patient’s initial adnexal
mass was not entirely removed at excisional biopsy and that its
remnants within the abdomen
later infiltrated the lower abdominal wall. It is also possible
that fragments of the original tumor were unknowingly sutured
into her Pfanennstiel incision
during the process of wound closure. Alternatively, the presently
expanding mass may not represent a recurrence of tumor encountered
at past operation,
but an entirely new and unrelated process. There is no clear-cut
answer to these issues because biopsy of the original lesion
showed inflammatory adhesions
at final pathology, a finding that may accurately depict the
lesion or reflect an unproductive biopsy attempt.
In conclusion, we present a case of abdominal cavity myolipoma with characteristic
pathology and imaging findings. Myolipoma is a rare soft tissue tumor that
is frequently large and deeply located, but clinically benign. This case was
unusual in that it herniated through the abdominal wall via a prior Pfannenstiel
incision into the subcutaneous tissue. Recognition of the intra- and extraperitoneal
location of this abdominal tumor was essential for accurate surgical planning.
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