AJR 2003; 181:1251-1254
© American Roentgen Ray Society
Imaging Characteristics of Spindle Cell Lipoma
Laura W. Bancroft1,
Mark J. Kransdorf1,2,
Jeffrey J. Peterson1,
Murali Sundaram3,
Mark D. Murphey2,4,5 and
Mary I. O'Connor6
1 Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL
32224-3899.
2 Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Walter Reed Army Medical Center, Bldg. #54, 6825 16th St., NW, Washington, DC
20306-6000.
3 Department of Radiology, Mayo Clinic, 200 1st St., Rochester, MN 55905.
4 Department of Radiology and Nuclear Medicine, Uniformed Services University of
the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799.
5 Department of Radiology, University of Maryland School of Medicine, 22 S
Greene St., Baltimore, MD 21201-1595.
6 Department of Orthopedic Surgery, Mayo Clinic, 4500 San Pablo Rd.,
Jacksonville, FL 32224-3899.
Received February 27, 2003;
accepted after revision May 14, 2003.
The opinions and assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Department of the Army or the Department of Defense.
Address correspondence to M. J. Kransdorf
(kransdorf.mark{at}mayo.edu).
Abstract
OBJECTIVE. The objective of this article is to define the imaging
characteristics of spindle cell lipoma on MRI and CT.
CONCLUSION. The diagnosis of spindle cell lipoma should be suggested
when a well-defined complex fatty mass is found in the subcutis of a
middle-aged man, especially if the mass is localized to the posterior neck.
Intense enhancement of the nonadipose component further supports this
diagnosis.
Introduction
Spindle cell lipoma was first described by Enzinger and Harvey
[1] in 1975 as a benign lesion
in which mature fat is replaced by collagen-forming spindle cells. In their
original description, these authors described spindle cell lipomas as
relatively common, yet they are perceived as rare by contemporary radiologists
because the lipomas are typically small and superficial and are often excised
without imaging. Consequently, there is scant literature documenting their
imaging appearance, with only scattered case reports. Knowledge of this
appearance is important because as a result of the variable ratio of adipose
and nonadipose soft tissue in these tumors, a spindle cell lipoma may mimic a
liposarcoma radiologically. In a 10-year review of soft-tissue tumors seen at
the Armed Forces Institute of Pathology, spindle cell lipoma was encountered
only slightly less frequently than well-differentiated liposarcoma
[2].
The objective of this article is to define the imaging characteristics of
spindle cell lipoma on MRI and CT.
Materials and Methods
This investigational protocol was conducted with the approval of the Mayo
Clinic institutional review board in accordance with the requirements of a
retrospective review. Informed consent was not required. We retrospectively
reviewed the MRI and CT scans of nine patients with histologically proven
spindle cell lipoma. Patients were selected from the archives of our
institution, chosen from a review of computer-generated patient diagnoses from
January 1996 through December 2000, supplemented by cases from the archives of
the Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Washington, DC.
Imaging characteristics were evaluated by three musculoskeletal
radiologists, with consensus on imaging findings. Studies reviewed consisted
of MRIs (eight patients, five with contrast administration), and
contrast-enhanced CT scans (three patients). Two patients were evaluated with
both imaging modalities. Radiologic features assessed included lesion size and
location, lesion margin and shape, presence or absence of intralesional
calcification, and percentage of lesion imaged similar to that of host adipose
tissue. This was graded as follows: 0, no fat; 1, greater than 0 to 25% fat;
2, greater than 25% to 50% fat; 3, greater than 50% to 75% fat; 4, greater
than 75% but not 100% fat; 5, 100% fat. Additionally, the nonadipose component
of the lesion was evaluated for character, attenuation and signal
characteristics, and pattern of enhancement. Gadolinium enhancement was graded
on extent (none, mild, moderate, or intense) and character (homogeneous,
heterogeneous, or linear and septal). Patient age and sex were also
recorded.
Results
All nine patients in our study group were men, each of whom had one lipoma.
The mean patient age was 54 years (range, 31–82 years). Tumor size
averaged 8.9 cm in greatest dimension (range, 2–29 cm). The spindle cell
lipomas typically were superficial, with eight (89%) located in the
subcutaneous fat. Only a single lesion in the thigh was intramuscular. The
posterior neck was the most common skeletal location, accounting for four
lesions (44%) (Fig. 1A,
1B,
1C). The remaining lesions were
located in the anterior neck, shoulder, forearm, thigh, and ischiorectal
fossa. All lesions were well circumscribed in all imaging planes. Eight
lipomas were ovoid, and one was lobulated. No intralesional calcification was
seen.
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Fig. 1A. —53-year-old man with spindle cell lipoma in subcutaneous
adipose tissue of posterior neck. Sagittal unenhanced T1-weighted image
(TR/TE, 550/13) shows ovoid, well-circumscribed tumor with fairly equal ratio
of adipose and nonadipose tissue.
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Fig. 1B. —53-year-old man with spindle cell lipoma in subcutaneous
adipose tissue of posterior neck. Sagittal fast spin-echo T2-weighted
fat-suppressed image (4,000/104) corresponding to A depicts
hyperintense nonadipose soft-tissue nodules, thick septa, and fat-suppressed
low-signal adipose components.
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Fig. 1C. —53-year-old man with spindle cell lipoma in subcutaneous
adipose tissue of posterior neck. Photomicrograph of histopathologic specimen
of spindle cell lipoma shows spindle cells (long straight arrow)
throughout specimen, scattered vascular channels (curved arrow), and
lipocytes (short straight arrow) in background of mucoid matrix. (H
and E, x100)
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On imaging studies, lesions consisted of between 0% and 95% fat, although
most lesions (seven of nine) contained between 25% and 75% fat, with a median
fat percentage grade of 2.2, corresponding to slightly more than 50% fat. The
nonadipose components of all lesions showed nonspecific signal
characteristics. Five of the lesions were more than half nonadipose tissue.
These five lesions contained variable amounts of adipose tissue that was best
characterized as globular (Figs.
1A,
1B,
1C and
2A,
2B,
2C,
2D). The globules of adipose
tissue had variable amounts of thin and thick septa. One of these five lesions
showed no radiologic fat (Fig.
3A,
3B,
3C), and one had the adipose
tissue localized predominantly at the periphery of the lesion. The four
remaining lesions showed a predominantly fatty character with variable amounts
of thick and thin septa and nodular nonadipose areas (Fig.
4A,
4B).
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Fig. 2A. —69-year-old man with spindle cell lipoma in ischiorectal
fossa. Axial unenhanced T1-weighted image (TR/TE, 690/15) shows well-defined
mass (arrows). Note relatively equal distribution of adipose and
nonadipose tissue, which is characteristic of spindle cell lipoma.
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Fig. 2B. —69-year-old man with spindle cell lipoma in ischiorectal
fossa. Axial fast spin-echo T2-weighted image (6,498/130) shows mass
(arrows) with similar distribution of adipose and nonadipose tissue.
Nonadipose components show signal intensity greater than that of fat.
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Fig. 2C. —69-year-old man with spindle cell lipoma in ischiorectal
fossa. Axial T1-weighted gadolinium-enhanced fat-suppressed image (450/15)
shows intense enhancement of nonadipose components of tumor (arrows).
High signal intensity in right ischium is due to nonuniform fat
suppression.
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Fig. 2D. —69-year-old man with spindle cell lipoma in ischiorectal
fossa. Axial contrast-enhanced CT image obtained through lower pelvis shows
well-circumscribed ovoid mass (black arrows) that contains both
adipose and markedly enhancing nonadipose tissue nodules. Thin septa
(white arrow) are also identified in medial portion of mass.
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Fig. 3A. —48-year-old man with spindle cell lipoma in subcutaneous
tissue of neck. Sagittal unenhanced T1-weighted image (TR/TE, 550/16) shows
well-defined 2-cm mass (arrows) with signal intensity similar to that
of muscle.
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Fig. 3B. —48-year-old man with spindle cell lipoma in subcutaneous
tissue of neck. Sagittal fast spin-echo T2-weighted image (3,500/98)
corresponding to A shows mass (arrows) to have signal
intensity similar to that of fat.
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Fig. 3C. —48-year-old man with spindle cell lipoma in subcutaneous
tissue of neck. Axial T1-weighted gadolinium-enhanced image (450/15) shows
intense enhancement (arrows) after IV gadolinium administration.
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Fig. 4B. —43-year-old man with spindle cell lipoma in subcutaneous
tissue of forearm. Axial fat-suppressed T2-weighted image (2,300/60)
corresponding to A shows scattered thin septa within mass
(arrows) and signal intensity slightly greater than that of adjacent
adipose tissue.
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The signal intensity of the nonspecific, nonadipose portion of all lesions
was greater than that of fat on conventional T2-weighted images, similar to or
greater than that of fat on fast spin-echo T2-weighted images, hyperintense on
fat-suppressed fluid-sensitive sequences, and similar to that of skeletal
muscle on T1-weighted images. The nonadipose tissue of all five tumors that
underwent gadolinium-enhanced MRI displayed intense enhancement equal to that
of the adjacent vessels.
Three patients underwent contrast-enhanced CT. The nonadipose tissue of two
of the spindle cell lipomas intensely enhanced to the same degree as that of
the adjacent vessels (Fig. 2A,
2B,
2C,
2D). The other tumor enhanced
less, with attenuation similar to that of the adjacent muscle.
Discussion
Spindle cell lipoma is a benign lesion that is cured by local excision and
has never been reported to metastasize. These slow-growing, usually solitary,
painless lipomatous variants typically present in men between the ages of 45
and 65 years. The mean age of patients in our study is similar to that of
patients in previous studies
[1,
2]. In their original report,
Enzinger and Harvey [1] noted
that these lesions typically occur in men, accounting for 91% (104/114) of
their patients. This trend was substantiated in a subsequent Armed Forces
Institute of Pathology report of 816 patients, in which 88% were men
[2]. In keeping with these
reports, all the patients in our study were men.
Spindle cell lipoma also has a significant tendency to occur in the
subcutaneous tissue of the posterior neck, shoulder, and back
[1,
3]. This anatomic tendency was
also seen in our study, with eight (89%) of the nine lesions occurring in the
subcutis, with only a single lesion occurring in an intramuscular location.
Intramuscular lesions have been previously reported
[4,
5]. Four (44%) of 11 lesions
occurred in the posterior neck. In the two large series previously noted, the
posterior neck and head and neck accounted for 36% and 41% of cases,
respectively [1,
2]. There is no explanation for
the predilection for the posterior neck, although this anatomic preference has
been used to support the designation of spindle cell lipoma as a distinct
entity. Tumors have also been reported in the extremities, oral cavity,
larynx, bronchus, orbit, scalp, breast, and perianal region
[4–7].
Braunschweig et al. [6]
reported an unusual case of spindle cell lipoma of the foot in which extensive
involvement resulted in pronounced erosion of several metatarsals, showing the
potentially locally infiltrative, aggressive nature of spindle cell lipoma. No
calcification or osseous erosion was noted in our series.
Before its designation as a separate entity, spindle cell lipoma was
frequently misdiagnosed pathologically as liposarcoma
[8,
9]. Microscopically, the lesion
is composed of mature fat with areas replaced by fibroblast-like spindle cells
within a matrix of mucin and collagen fibrils
[10]
(Fig. 1C). Although most
spindle cell lipomas are composed of a relatively equal ratio of fat and
spindle cells, either component may predominate, and the variation in the
ratio of fat and spindle cells causes the wide spectrum of imaging features.
In our series, seven (78%) of the nine lesions had relatively similar amounts
of both adipose and nonadipose tissue, being composed of between 25% and 75%
fat. Only two lesions showed a dominant component, with one lesion completely
composed of soft tissue and one lesion predominantly composed of fat.
The vascular pattern of spindle cell lipoma is usually inconspicuous,
although some tumors have a prominent plexiform vascular pattern, similar to
that of myxoid liposarcoma
[11], and a
hemangiopericytoma-like vascular pattern or a pseudoangiomatous variant has
been described [12]. This
prominent vascularity most likely accounts for the intense enhancement in the
nonadipose components of the spindle cell lipomas in our series. In our
experience, this enhancement is significantly more intense than that seen in
liposarcoma.
The imaging appearance of spindle cell lipoma is not pathognomonic and,
like most other musculoskeletal tumors, displays a spectrum of features. In
the case of spindle cell lipoma, these features may overlap with those of
liposarcoma. The diagnosis of spindle cell lipoma, however, should be
suggested when a middle-aged man presents with a well-defined complex fatty
mass in the subcutis, especially when localized to the posterior neck. Intense
enhancement of the nonadipose component further supports this diagnosis.
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Abstract
Introduction
