Diagnostically Challenging Spindle Cell Lipomas: A Report of 34 “Low-Fat” and “Fat-Free” Variants

Mayo Clinic - Rochester, Рочестер, Minnesota, United States
American Journal of Dermatopathology (Impact Factor: 1.39). 10/2007; 29(5):437-42. DOI: 10.1097/DAD.0b013e31813735df
Source: PubMed

ABSTRACT

Spindle cell lipomas (SCL) classically occur as subcutaneous masses in the upper trunk/neck of older men and are composed of mature fat, CD34-positive spindled cells, ropey collagen, myxoid matrix, and blood vessels. A number of variants have been reported, including SCL with pseudoangiomatous change, composite SCL hibernoma, and composite SCL/pleomorphic lipoma. A review of over 300 consultation cases diagnosed as SCL revealed 34 cases in which fat was noted to be present in <5% of the tumor (n = 30) or absent (n = 4). These cases posed diagnostic difficulties because of the dearth of fat; we propose the terms "low-fat" and "fat-free" SCL for these variants. The tumors presented in older men (mean, 56 years; ratio of males to females, 11:1) and presented as small (mean, 2.0 cm) circumscribed dermal or subcutaneous masses of the head/neck (n = 18), back (n = 7), shoulder (n = 5), leg (n = 2), arm (n = 1), or unknown location (n = 1). In the majority, referring pathologists considered benign diagnoses, usually benign nerve sheath tumors, but in four cases low-grade sarcoma was considered. In only three cases was SCL considered. The tumors were composed of aggregates of CD34-positive, bland spindled cells arranged in characteristic parallel arrays, admixed with ropey collagen and myxoid matrix. Isolated clusters or single adipocytes were present in 30 cases; four were devoid of fat. CD34 was diffusely positive (10/11). A high index of suspicion based on clinical context and identification of other typical features of SCL are key features to the diagnosis of low-fat and fat-free SCL.

Full-text

Available from: Steven D Billings
ORIGINAL ARTICLE
Diagnostically Challenging Spindle Cell Lipomas: AReport
of 34 ‘‘Low-Fat’’ and ‘‘Fat-Free’’ Variants
Steven D. Billings, MD* and Andrew L. Folpe, MD†
Abstract: Spindle cell lipomas (SCL) classically occur as sub-
cutaneous masses in the upper trunk/neck of older men and are
composed of mature fat, CD34-positive spindled cells, ropey
collagen, myxoid matrix, and blood vessels. A number of variants
have been reported, including SCL with pseudoangiomatous change,
composite SCL hibernoma, and composite SCL/pleomorphic lipoma.
A review of over 300 consultation cases diagnosed as SCL revealed
34 cases in which fat was noted to be present in ,5% of the tumor
(n = 30) or absent (n = 4). These cases posed diagnostic difficulties
because of the dearth of fat; we propose the terms ‘low-fat’ and ‘fat-
free’ SCL for these variants. The tumors presented in older men
(mean, 56 years; ratio of males to females, 11:1) and presented as
small (mean, 2.0 cm) circumscribed dermal or subcutaneous masses
of the head/neck (n = 18), back (n = 7), shoulder (n = 5), leg (n = 2),
arm (n = 1), or unknown location (n = 1). In the majority, referring
pathologists considered benign diagnoses, usually benign nerve
sheath tumors, but in four cases low-grade sarcoma was considered.
In only three cases was SCL considered. The tumors were composed
of aggregates of CD34-positive, bland spindled cells arranged in
characteristic parallel arrays, admixed with ropey collagen and
myxoid matrix. Isolated clusters or single adipocytes were present in
30 cases; four were devoid of fat. CD34 was diffusely positive
(10/11). A high index of suspicion based on clinical context and
identification of other typical features of SCL are key features to the
diagnosis of low-fat and fat-free SCL.
Key Words: low-fat spindle cell lipoma, fat-free spindle cell lipoma,
spindle cell lipoma, skin neoplasms
(Am J Dermatopathol 2007;29:437–442)
S
pindle cell lipoma classically occurs as a solitary, sub-
cutaneous, circumscribed lesion in the posterior back,
neck, or shoulders of older men.
1
Histologically, classic
spindle cell lipoma is variably composed of mature fat,
cytologically bland, CD34-positive spindled cells arranged in
characteristic parallel arrays (‘‘school of fish’’), ropey
collagen, myxoid matrix, and blood vessels. In the majority
of cases, the diagnosis is relatively straightforward. However,
a number of described spindle cell lipoma variants can cause
diagnostic difficulties due to variations in these combinational
elements or by virtue of histologic features that differ from the
prototypical spindle cell lipoma. These variants include
pseudoangiomatous spindle cell lipoma, vascular spindle cell
lipoma, fibrous spindle cell lipoma, plexiform spindle cell
lipoma, composite spindle cell lipoma-hibernoma, and
composite spindle cell lipoma-pleomorphic lipoma.
2–11
It is
recognized that the amount of fat in spindle cell lipoma is
variable, and in some cases fat is present in only small
amounts.
1,12
However, this phenomenon does not seem to be
well recognized among pathologists and dermatopathologists.
Over the past several years, we have encountered in consul-
tation a number of spindle cell lipomas that have caused
diagnostic problems for the referring pathologists or derma-
topathologists because of a dearth of intralesional fat. We
report our experience with 34 cases of spindle cell lipomas
with little to no fat.
MATERIALS AND METHODS
We reviewed the consultation reports from over 300
consultation cases previously coded as ‘spindle cell lipoma’
for cases in which we had specifically commented on the near-
total or total absence of intralesional fat, either in the text of
the letter or in the diagnostic line. With the exception of the
near or total absence of fat, all of these tumors displayed
features identical to ordinary spindle cell lipomas, as described
above. All such cases were rereviewed by both authors, and
cases either entirely devoid of mature fat or with only rare
mature adipocytes comprising ,5% of the tumor were
included in this study. Accompanying immunohistochemical
stains for CD34, S-100 protein, actin, and desmin were
available for review in some cases. In selected cases,
immunostains for CD34 (DakoCytomation, Carpenteria,
CA; prediluted) were performed at the time of consultation
with standard streptavidin-biotin technique and heat-induced
epitope retrieval using a heated water bath.
RESULTS
Thirty-four cases were identified (Table 1). The tumors
predominantly occurred in men (male-to-female ratio, 11:1)
with a mean age of 56 years. The tumors typically presented as
asymptomatic, small (mean size, 2.0 cm) subcutaneous masses
involving the head and neck (n = 18), back (n = 7), shoulder
(n = 5), lower extremity (n = 2), and upper extremity (n = 1).
For one case, the location was not available. The differential
From the *Department of Anatomic Pathology, Cleveland Clinic, Cleveland,
OH; and Division of Anatomic Pathology, Mayo Clinic, Rochester, MN.
Correspondence: Steven D. Billings, MD, Department of Anatomic Pathology,
Cleveland Clinic, 9500 Euclid Avenue L25, Cleveland, OH 44195
(e-mail: billins@ccf.org).
Copyright Ó 2007 by Lippincott Williams & Wilkins
Am J Dermatopathol
Volume 29, Number 5, October 2007 437
Page 1
diagnosis considered by referring pathologists and dermato-
pathologists was broad. In most cases the diagnoses con-
sidered were benign entities including neurofibroma, solitary
fibrous tumor, cutaneous myxoma (superficial angiomyxoma)
or a descriptive diagnosis of a benign mesenchymal or myxoid
tumor not further classified. In four cases the referring
pathologist considered the diagnosis of a low grade sarcoma.
In only three cases was the diagnosis of spindle cell lipoma
considered.
Microscopically the tumors were in all instances well
circumscribed. The majority were located in the subcutis. One
tumor was located in the dermis, and a minority of cases
showed secondar y involvement of the dermis. There were no
differences in morphologic features depending on location in
subcutis, dermis, or both.
When present, the adipocytes comprised less than 5% of
the tumor and were present in small clusters or as isolated,
single adipocytes (Figs. 1A, B). Four cases were entirely
devoid of mature adipocytes. All of the tumors appeared to be
adequately sampled (approximately 1 section per centimeter).
All of the tumors were composed of a proliferation of bland
spindled cells with small fusiform nuclei, typically arranged in
small parallel groups, within a myxoid to collagenous stroma.
In 16 cases, the stroma was predominantly myxoid (Figs. 1A
and 2), occasionally forming myxoid pools. In the pre-
dominantly myxoid tumors, the tumor cells generally had
a more random, dispersed arrangement. In eight cases, the
stroma was predominantly collagenous (Figs. 1B and 3). In
two cases, the tumors had areas of mat-like collagen similar to
that seen in solitary fibrous tumor, but lacked the staghorn
vessels and ‘patternless’ growth pattern diagnostic of that
entity. Additionally, these two cases displayed the character-
istic ropey collagen seen in spindle cell lipoma. The remaining
case had a mixture of myxoid and collagenous stroma. In the
cases with the mixed or predominantly collagenous stroma, the
TABLE 1. Summary of Clinical Features
Case
Age
(Years) Sex Site
Size
(cm) Referring Diagnosis
1 33 M Scalp 2.4 Benign myxoid tumor
2 78 M Back 2.5 Myxoid neurofibroma
3 33 F Foot 1.1 NA
4 48 M Thigh 4.0 Angiomyxoma
5 70 M Neck NA NA
6 54 M Neck 2.2 Atypical lipoma
7 50 M Shoulder 2.0 Spindle cell lipoma vs.
low-grade sarcoma
8 51 M Neck 1.3 Benign myxoid tumor
9 47 F Neck 1.7 Solitary fibrous tumor
10 58 M Back 2.0 Spindle cell lipoma
11 54 M Scalp 3.5 NA
12 46 M NA NA NA
13 74 M Shoulder 2.8 Benign nerve sheath tumor
14 59 M Back 2.7 Benign mesenchymal tumor
15 59 M Neck 2.5 Angiomyxoma
16 76 M Neck 1.0 Benign nerve sheath tumor
17 61 M Back 9.0 NA
18 75 M Shoulder 2.8 Myxoma
19 79 M Back 1.7 Neurofibroma
20 58 M Neck NA NA
21 84 M Neck 3.5 NA
22 43 M Neck 4.5 NA
23 76 M Back 4.5 Myxofibrosarcoma vs. angiomyxoma
24 63 M Neck 2.5 Low-grade sarcoma
25 52 M Back 2.2 Low-grade fibromyxoid sarcoma
26 57 M Face 4.3 Benign mesenchymal tumor
27 52 M Shoulder 2.2 Spindle cell lipoma vs.
solitary fibrous tumor
28 40 M Scalp 1.5 Neurofibroma
29 46 M Shoulder NA Reactive process
30 64 M Scalp 1.5 NA
31 46 M Scalp 1.7 NA
32 40 M Scalp 2.5 NA
33 41 F Neck 2.0 NA
34 40 M Wrist 2.4 NA
NA, not available.
FIGURE 1. When present, mature adipocytes were present in
small clusters (A) or isolated single fat cells (B).
438 q 2007 Lippincott Williams & Wilkins
Billings and Folpe Am J Dermatopathol
Volume 29, Number 5, October 2007
Page 2
tumor cells were frequently arranged in short parallel bundles
with nuclear palisading (Fig. 3). Nuclear pleomorphism and/or
floret cells similar to the floret cells of pleomorphic lipoma
were rare, present in only two cases (Fig. 4). All cases had the
wiry to ropey collagen characteristic of spindle cell lipoma
(Fig. 5). Fifteen cases had a curvilinear vasculature with
prominent perivascular hyalinization (Fig. 6). One case had
a delicate plexiform vasculature similar to myxoid liposarcoma
(Fig. 7), and one had a hemangiopericytomatous vasculature.
Pseudovascular spaces were prominent in one case (Fig. 8).
The vasculature was inconspicuous in the remaining cases. All
of the tumors had some scattered mast cells. In 11 cases,
immunostains were available for review or performed in the
evaluation of the tumor at the time of consultation. Diffuse
immunoreactivity for CD34 was present in 10 of 11 cases
(Fig. 9). Immunostains for S100 protein only highlighted
rare mature adipocytes and not the spindled cell component.
The spindled cells were also negative for actins and desmin.
DISCUSSION
Although spindle cell lipoma is notoriously histologi-
cally protean, its diagnosis is in most cases fairly straightfor-
ward, owing to its characteristic clinical presentation and
histologic features.
1,12–14
Most spindle cell lipomas exhibit the
prototypical histologic features of bland spindled cells, often
arranged in short parallel bundles, admixed with mature
FIGURE 3. Short bundles of spindled cells with nuclear
palisading were present in the majority of tumors. This growth
pattern was more apparent in tumors with a mixed collage-
nous and myxoid stroma and in tumors with a purely
collagenous stromal background.
FIGURE 4. Focal pleomorphism was present in two cases.
FIGURE 5. All of the cases had areas with wiry to ropey collagen
characteristic of spindle cell lipoma. This case also had a parallel
arrangement of the spindled cells.
FIGURE 2. The stroma was predominantly myxoid in sixteen
cases. In tumors with a predominantly myxoid stroma, the
tumor cells frequently had a random growth pattern, without
the bundled arrangement of spindled cells commonly seen
in spindle cell lipoma. These features frequently caused
diagnostic difficulty.
q 2007 Lippincott Williams & Wilkins
439
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Page 3
adipocytes. The ratio of the spindled cells and mature
adipocytes is variable, but the great majority of cases have
significant amounts of both components. The spindled cell
component is composed of short fusiform cells that are
immunoreactive for CD34.
15,16
The stromal backg round
contains wiry to ropey collagen and myxoid matrix.
A variety of variants of spindle cell lipoma have been
described including pseudoangiomatous, fibrous, vascular,
plexiform, and composite spindle cell lipomas.
2–6,8–11
Although spindle cell lipomas with little fat were mentioned
in the original series described by Enzinger and Harvey,
1
cases
with little to no fat remain diagnostically challenging. No
previous study has emphasized this problem. Almost all of
our cases had the typical clinical presentation of spindle cell
lipoma. They presented as small tumors of the head and neck,
upper back, or shoulders of older men. Rare cases occurred in
the extremities, as has been previously described.
1,14,17
The key to the microscopic diagnosis of low-fat and fat-
free spindle cell lipomas is recognition that the spindled cells
are histologically identical to the spindled cell population of
conventional spindle cell lipoma. In almost all cases in this
series, close inspection reveals the spindled cells to be
arranged in short parallel bundles, as in ordinary spindle cell
lipomas.
1,12–14
The tumors with prominent myxoid stroma
caused the most diagnostic difficulty. Spindle cell lipoma has
a variably myxoid to collagenous stroma, and it is important to
keep in mind that spindle cell lipoma may be a predominantly
FIGURE 6. Perivascular hyalinization was prominent in 15
cases. The spindled cells in this case were arranged in short
fascicles with a parallel arrangement of the tumor nuclei.
FIGURE 7. A delicate plexiform vasculature similar to myxoid
liposarcoma was present in one case. The tumor cells were
morphologically identical to the spindled cells of spindle cell
lipoma. No lipoblasts were present.
FIGURE 8. One case had prominent pseudovascular spaces
similar to the pseudoangiomatous variant of spindle cell
lipoma. Note the presence of the short bundles of spindled
cells and the ropey collagen characteristic of spindle cell
lipoma.
FIGURE 9. The spindled cells were diffusely immunoreactive
for CD34.
440 q 2007 Lippincott Williams & Wilkins
Billings and Folpe Am J Dermatopathol
Volume 29, Number 5, October 2007
Page 4
myxoid tumor. In myxoid tumors, the spindled cells often have
a somewhat more random arrangement rather than in tumors
with a more collagenous or mixed background. However, the
tumor cells and the wiry collagen seen in myxoid cases are
identical to those seen in ordinar y spindle cell lipomas.
Ironically, the presence of adipocytes was the least
helpful feature. In the low-fat tumors, they were scattered
single adipocytes or very small clusters of adipocytes.
Admittedly, it is possible that additional sampling could have
detected rare adipocytes in the fat-free tumors, but these
tumors appear to have been adequately sampled, with at least
one section submitted per centimeter of tumor.
In selected cases, immunohistochemical stains may be
helpful. The spindle cell component of spindle cell lipomas
shows strong immunoreactivity for CD34.
15,16
This needs to be
interpreted in the appropriate histologic context, however, as
expression of CD34 is relatively nonspecific and occurs in
a variety of mesenchymal neoplasms.
The potential diagnostic difficulty caused by the low-fat
and fat-free spindle cell lipoma is highlighted by the broad
differential diagnosis considered by contributing pathologists,
dermatologists, and dermatopathologists. Although most cases
were referred with a suggested benign diagnosis, the diagnosis
of spindle cell lipoma was considered in just three cases.
The most common benign entities in the differential diagnosis
were benign nerve sheath tumors including neurofibroma.
Neurofibroma is composed of spindled cells with comma-
shaped nuclei and the stromal collagen is more delicate in
neurofibroma. Although some admixed CD34-positive cells
are frequently seen in neurofibroma,
18,19
immunohistochem-
ical stains for S100 protein highlight the majority of the
spindled cells.
Superficial angiomyxoma (cutaneous myxoma) was also
considered in the differential diagnosis of myxoid fat-free
spindle cell lipomas. The tumor cells in superficial angiomyx-
oma are always randomly arranged and have a spindled to
stellate morphology.
20–22
Superficial angiomyxoma lacks ropey
collagen, and the vasculature is typically more delicate. The
presence of scattered neutrophils and/or entrapped epithelial
structures may be helpful clues in the diagnosis of superficial
angiomyxoma.
In the more collagenous tumors, solitar y fibrous tumor
was also a consideration. Solitary fibrous tumor most
frequently presents as a pleural mass, but rare cutaneous
lesions have been reported.
23,24
Solitary fibrous tumors may
rarely have associated adipocytes, which could further cloud
the issue.
25
In this series, two of the cases had focal areas of
mat-like collagen similar to solitary fibrous tumor. However,
these cases also had zones with a more organized growth
pattern with nuclear palisading rather than the patternless
pattern of solitary fibrous tumor. Admittedly, the distinction
could be very difficult if not impossible in selected cases, and
some authors have suggested that spindle cell lipoma and
solitary fibrous tumors are part of a related group of CD34-
positive spindle cell tumors.
26
We believe that distinction is
possible in the majority of cases given the clinical presentation
and presence in areas of typical features of spindle cell lipoma.
A low-grade sarcoma, specifically low-grade myxofi-
brosarcoma and low-grade fibromyxoid sarcoma, was
considered in the differential diagnosis in a few cases.
Although both of these tumors may present as superficial
lesions, neither typically involves the upper trunk or head and
neck area.
27–32
Low-grade myxofibrosarcoma tends to be
purely myxoid and has more diffuse nuclear atypia. Low-grade
fibromyxoid sarcoma has a variably myxoid to collagenous
stroma and often has associated collagen rosettes.
27,31–34
Superficial low-grade fibromyxoid sarcoma usually presents
in younger patients, most frequently on the extremities.
27
Both
low-grade fibromyxoid sarcoma and myxofibrosarcoma
usually lack strong CD34 expression, but CD34-positive cells
may be seen in these entities.
In summar y, low-fat and fat-free spindle cell lipoma are
uncommon and frequently mistaken for other entities. Cases
such as these underscore an important but easily forgotten
principle in the diagnosis of adipocytic neoplasms—that the
key to their diagnosis lies in the nonlipogenic, rather than
lipogenic, component. Examples of this include the arborizing
capillary network of myxoid liposarcoma, the irregular fibrous
septa containing enlarged hyperchromatic cells in atypical
lipomatous tumor/well-differentiated liposarcoma, and, as we
have emphasized here, the parallel arrays of bland spindled
cells and stromal background in spindle cell lipoma. Careful
attention to these histologic features and clinical correlation
should allow for the distinction of rare fat-free spindle cell
lipomas from their various benign and malignant morphologic
mimics.
ACKNOWLEDGMENT
We thank Dr. Sharon W. Weiss for facilitating the study of
cases from the Emory University Soft Tissue Consultation
Service archives.
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    • "SCLs are fairly well-circumscribed, subcutaneous tumors that are composed of varying proportions of mature fat cells, small and uniform spindle cells and eosinophilic collagen bundles [1,3,4]. The stroma can range from collagenous to myxoid [3,4]. Intramuscular lesions of this tumor are very rare. "
    [Show abstract] [Hide abstract] ABSTRACT: Spindle cell lipoma is an uncommon adipocytic tumor. Intramuscular lesions of this tumor are very rare. In this report, we describe a case of a patient with intramuscular spindle cell lipoma localized in a deltoid. A 58-year-old Japanese man visited us because of a soft tissue mass on the lateral aspect of the left shoulder that had been noticed 2 years prior. The spherical tumor, which measured 5cm×4cm, was elastic and firm on palpation and immobile. Magnetic resonance imaging revealed that the lesion was localized in the left deltoid muscle. A needle biopsy was performed to make a histological diagnosis. With a pre-operative diagnosis of intramuscular lipoma, we removed the tumor with the patient under general anesthesia. The tumor was removed with surrounding musculature and fascia. The pathological diagnosis was intramuscular spindle cell lipoma in the left deltoid muscle. There are several kinds of lipomas. Spindle cell lipoma is a relatively rare variant (1.5% of all adipocytic neoplasms) that is histologically distinct and characterized by the replacement of mature fat by a mixture of mature adipocytes and undifferentiated spindle cells. There are only five other reported cases of intramuscular spindle cell lipoma in the literature, to our knowledge. The case of our patient is very interesting, as to date there have been few reported patients with a diagnosis of an intramuscular spindle cell lipoma in a deltoid.
    Full-text · Article · Dec 2015 · Journal of Medical Case Reports
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    • "The histological differential diagnosis of SCL depends on features that predominate in each lesion. It usually includes benign tumors such as classic lipoma, schwannoma, neurofibroma [7], leiomyoma [1], and solitary fibrous tumor [16]. However, atypical lipomatous tumors (ALT) may also represent a differential diagnosis of SCL [7]. "
    [Show abstract] [Hide abstract] ABSTRACT: Spindle cell lipoma is a benign lipomatous neoplasm, which rarely occurs in the oral cavity. The aims of this paper are to report a case of spindle cell lipoma located in buccal mucosa and discuss the main clinical, histological, and immunohistochemical findings of this entity. Thus, we report a 4-year history of an asymptomatic smooth surface nodule in an elderly Caucasian man with clinical hypothesis of fibroma. The histopathological examination showed spindle cells, mature adipose tissue, and many mast cells in a stroma of connective tissue presenting ropey collagen fibers bundles. After immunohistochemical analysis, the final diagnosis was spindle cell lipoma.
    Full-text · Article · Oct 2015
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    • "Lipoblasts and floret cells are commonly absent in SCL. Immunohistochemically , CD34 expression is diffuse and strong in SCL [5, 6], while weak or absent in WSLS. SCLS must also be differentiated. "
    [Show abstract] [Hide abstract] ABSTRACT: Spindle cell lipoma (SCL) is a rare, benign adipocytic tumor commonly arising in the upper neck, back, and shoulder regions. To the best of our knowledge, only one case of SCL of the wrist has previously been reported. We herein report a rare case of SCL arising at the wrist. A 77-year-old man presented with a 4-year history of a mass in the right wrist. Radiography showed no significant findings, and magnetic resonance imaging demonstrated the presence of a mass on the radial dorsal side of the right wrist. Needle biopsy suggested the tumor was SCL, and total excision was performed. Macroscopically, the tumor was circumscribed by fibrous membrane with a yellowish to partly white surface. Histologically, the tumor was composed of mature adipocytes and proliferation of the less atypical spindle cells in a ropey-like collagen background. Immunohistochemically, the tumor cells showed diffuse and strong expression for CD34. The final diagnosis of SCL was made on the basis of these pathological and radiological findings. The patient was successfully treated and shows no evidence of disease at 3 months after surgery.
    Full-text · Article · Mar 2015 · International journal of clinical and experimental pathology
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