2020, Volume 36, Number 2, Page(s) 126-134
Cutaneous Smooth Muscle Tumors: A Clinicopathological Study Focusing on the Under-Recognized Histological Features
Asuman KILITCI1, Ömer Faruk ELMAS2
1Department of Pathology, Ahi Evran University School of Medicine, KIRŞEHIR, TURKEY
2Department of Dermatology, Ahi Evran University School of Medicine, KIRŞEHIR, TURKEY
Keywords: Cutaneous, Smooth muscle tumor, Piloleiomyoma, Angioleiomyoma, Leiomyosarcoma
Cutaneous smooth muscle tumors represent a rare group of cutaneous lesions including piloleiomyoma, angioleiomyoma, genital
leiomyoma, smooth muscle hamartoma, and leiomyosarcoma. In this study, we aimed to evaluate the clinical and pathological characteristics of
CSMTs, focusing on the rare and unspecified histological features.
Material and Method: The clinical, demographic and histological findings of the patients with CSMTs were reviewed and evaluated retrospectively.
The histopathological sections were re-evaluated for all cases.
Results: A total of 32 patients with CSMTs were enrolled. The majority were female (n=20). The most common tumor diagnosed was
angioleiomyoma (n=19, 59.4%) followed by piloleiomyoma (n=8, 25%), smooth muscle hamartoma (n=2, 6.3%), leiomyosarcoma (n=2, 6.3%),
and genital leiomyoma (n=1, 3%). Five lesions were painful and only 3 specimens were submitted with the preliminary diagnosis of a cutaneous
smooth muscle tumor.
Conclusion: There are very few studies investigating both clinical and histological characteristics of CSMTs in detail. Along with the classical
histological clues, evaluation of the clinical findings and less-defined histological features may enhance the diagnostic accuracy. To the best of our
knowledge, this study represents the first original study focusing on the clinical and pathological aspects of CSMTs in our country.
Cutaneous smooth muscle tumors (CSMTs) refer to a rare
group of cutaneous tumors originating from piloerector
smooth muscles, vascular smooth muscles or specialized
soft tissues of the genital area 1,2
Benign CSMTs mainly include piloleiomyoma (PLM),
angioleiomyoma (ALM), genital leiomyoma (GLM) and
smooth muscle hamartoma (SMH). PLM originates from
the piloerector muscle while ALM arises from the tunica
media of the vessel wall. GLM originates from the dartos
muscle and nipple smooth muscle fibrils. SMH refers to
the presence of congenital or acquired irregular smooth
muscle bundles in the dermis 1,2. Leiomyosarcoma
(LMS) describes the proliferation of smooth muscle tumors
with a malignant nature 1.
There are a few original studies investigating clinicopathological
features of CSMTs in the relevant literature and
most of the studies covering the histopathological aspect of
CSMTs are small case series or single case reports 3-10. In this study, we aimed to evaluate the clinical and pathological
characteristics of benign and malignant CSMTs, focusing
on the rare and unspecified histological features.
This study was conducted at a tertiary hospital. The clinical,
demographic and histological findings of the patients
with CSMTs were reviewed and evaluated retrospectively.
Demographic and clinical parameters such as age, site,
number of lesions, preliminary diagnoses, pain status,
recurrence, metastasis and sending department were
obtained from the patient records. All the histological slides
were re-evaluated in detail and the histomorphological
findings (growth pattern, epidermal changes, presence of
inflammation, degenerative changes, mitosis, necrosis,
cellular atypia, presence of nerve fiber, presence of hair
follicle and eccrine gland, vascular structures, lesions
extension) were recorded. The tumor subtypes were
identified, and the clinical and pathological findings were
The statistical analyses conducted with the Statistical
Package for Social Sciences version 21.0 software for
Windows (IBM SPSS Statistics for Windows Version
21.0. Armonk, NY: IBM Corp., USA). The assumption of
normality for quantitative variables was tested with the
Kolmogorov-Smirnov and Shapiro-Wilk tests. The Chi-
Square, Kruskal Wallis and ANOVA tests were employed
for the univariate analysis of the variables in the study
according to the type of the variables and the assumptions.
The explanatory statistics of the variables are given as
mean ± standard deviation, median, and frequencies (n).
The p values below 0.05 were considered to be statistically
significant in all analyses.
All procedures followed the Helsinki Declaration and the
study was approved by the local clinical research ethics
committee (Decision no: 2019-02/26).
A total of 32 patients were enrolled in the study; 20 (62.5%)
of these were female and 12 were (37.5%) male. The
mean ages of the female and male patients were 48.5 and
55.2 years, respectively, with no statistically significant
difference. Demographic features and the mean sizes of the
lesions have been summarized in Table I
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|Table I: Distributions of the mean age, gender and mean tumor diameters in different subtypes of CSMTs.
Pain was the only symptom reported and was present in
five cases. There were no patients with a personal or familial
history of cutaneous or extracutaneous leiomyomas. The
most common clinical preliminary diagnosis reported was
lipoma (n=4) followed by leiomyoma (n=3), sebaceous
cyst (n=2), dermatofibroma (n=2), cyst (n=2), fibroma
(n=1), neurofibroma (n=1), schwannoma (n=1), mycosis
fungoides (n=1), morphea (n=1), bursitis (n=1), sarcoma
(n=1), lymphadenopathy (n=1), hemangioma (n=1),
keloidal scarring (n=1), and Bartholin gland cyst (n=1). All
patients presented with solitary lesions except for a patient
with multiple PLMs. In this case of multiple leiomyomas,
computed tomography scans showed no evidence of
concomitant visceral tumors. None of the female patients
had simultaneous uterine and cutaneous leiomyomas.
The most frequent sites involved were the extremities (n=4,
71.9%) followed by the breast (n=4), back (n=2), face (n=1), vulva (n=1), and gluteal region (n=1). The most common
tumor diagnosed was angioleiomyoma (n=19, 59.4%)
followed by piloleiomyoma (n=8, 25%), smooth muscle
hamartoma (n=2, 6.3%), leiomyosarcoma (n=2, 6.3%),
and genital leiomyoma (n=1, 3%). No recurrences were
determined in the follow-up visits for at least 1 year. The
histological subtypes, locations and provisional diagnoses
of the lesions are presented in Table II.
The mean tumor diameter was 1.6 cm, ranging from 0.75 to
7 cm. The mean diameters of the ALMs, PLMs, and SMHs
showed no statistically significant difference. The largest
tumor diameter was 7.0 cm in an LMS while the smallest
one was 0.75 cm in a PLM. The mean sizes of each lesion
subtype are shown in Table I.
All of the ALMs showed smooth-bordered, round and
nodular growth patterns. Most of the ALMs (n=12) were
limited to the lower half of the dermis while seven ALMs
extended into subcutaneous fat. Four ALMs demonstrated
hyalinization while two ALMs had cystic degeneration.
Calcification of the vessel walls was observed in one ALM
case, while another one showed myxoid degeneration.
Adipocytes were also detected in an ALM. Two ALMs
had mild epidermal hyperplasia while two others showed
basal epidermal pigmentation. Seven ALMs had a mild
chronic inflammatory cell infiltration while one showed a
moderate infiltration. No hair follicles and eccrine glands
involvement were observed in ALMs. The overwhelming
majority of ALMs (n=15, 79%) had only thin-walled vessels
while three (15.8%) ALMs had both thin- and thick-walled
vessels. Only one (5.2%) ALM showed the involvement of
thick-walled vessels alone (Figure 1A-D).
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|Figure 1: Angioleiomyoma. A) Thin-walled vascular channels (small veins) (H&E; x100). B) Thin and thick-walled vascular channels
(H&E; x50). C) Calcification of the vascular walls and hyalinization (H&E;x50). D) Myxoid changes (H&E; x50).
All PLMs demonstrated an irregular growth pattern that
stretched from the upper dermis to the lower dermis. In
two PLMs, muscle fibers were also observed among the rete
ridges. All PLMs showed mild (n=5) or moderate (n=3)
epidermal hyperplasia, while most of them (n=7) showed
pigmented rete ridges. Entrapped hair follicles and eccrine
glands were observed in all PLMs. Fat cells were detected in
only one PLM (Figure 2A-D). None of the ALMs or PLMs
showed necrotic changes.
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|Figure 2: Piloleiomyoma. A) Epidermal hyperplasia (H&E; x50). B) Basal hyperpigmentation (H&E; x50). C) Entrapped eccrine glands
(H&E; x100). D) Entrapped hair follicle in PLM (H&E; x50).
Both SMHs showed numerous well-defined smooth muscle
bundles of varying orientation distributed throughout the
dermis. While both cases had different degrees of epidermal
hyperplasia, one of them also had nerve bundles (Figure
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|Figure 3: A,B) Smooth muscle hamartoma in two patients. Variable shape, size, and orientation of the smooth muscle bundles in the
upper dermis (H&E; x50).
Both LMSs were characterized by a poorly circumscribed
nodule comprised of a spindle cell proliferation forming
rough bundles and fascicles. Necrosis was present in both
LMSs while while only one of them showed atypical mitosis
and ulceration (Figures 4A-D; 5A,B). The histopathological
features detected in different subtypes of CSMTs have been
demonstrated in Table III.
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|Figure 4: A) Leiomyosarcoma (H&E; x50). B) Ulceration (H&E; x50). C) Hyaline degeneration (H&E; x100). D) Myxoid changes (H&E;
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|Figure 5: Leiomyosarcoma. A) Chronic inflammatory cell infiltration around the tumor (H&E; x100). B) Tumor necrosis (H&E; x50).
The immunohistochemical examination confirmed the
diagnosis in all of the lesions, showing uniformly positive staining with desmin and smooth muscle actin (SMA).
When comparing with desmin, SMA staining was less
intense in 5 ALMs, 5 PLMs, and 2 LMSs. The remaining
cases showed no remarkable differences in terms of staining
patterns and intensities. In 19 cases, we used additional
immunohistochemical stains (CD 31, CD34, PanCK,
CD68, S100) to exclude possible differentials including
fibrohistiocytic tumors, hemangiomas, and peripheral
nerve sheath tumors but the results of these stains turned
out to be negative, except for S100 and CD68. The last two
stains showed focal-weak staining in 3 ALMs and one PLM.
A statistically significant difference was detected between
histopathological findings and histopathological subtypes
(p= 0.000), which has been detailed in Table III.
Cutaneous leiomyomas represent nearly 5 percent of
all leiomyomas and are more common in adults than
in children. Most of the studies have reported a male
. Unlike these studies, our study showed
a slight female predominance but this difference was
statistically insignificant. A higher rate of cosmetic concerns
in women may explain this slight female predominance.
CSMTs may be painful possibly due to the pressure on the
nerve bundles or the contraction of the muscle fibers. Pain
in CSMTs has been reported as high as 54.1% of the patients
in the literature 7. In our study, only 16% of the lesions
were painful. Entrapped peripheral nerve sections were detected only in an ALM and two PLMs while one ALM
and 6 PLMs demonstrated nerve fibers around the lesions.
The paucity of the entrapped peripheral nerve fibers may
explain the lower rate of pain reported in the present study.
There was no statistically significant difference between
pain status and tumor subtypes, gender, age, site and size of
the lesions. The clinical and histopathological differential
diagnoses of CSMTs should include the other painful
tumors, which are dermatofibroma, eccrine spiradenoma,
schwannoma, giant cell tumor of the tendon sheath, glomus
tumor, hemangioma, and lipoma 11. In this study, only
3 (9.3%) patients had a preliminary clinical diagnosis of
leiomyoma. The rates of an accurate preliminary diagnosis
have also been reported to be low in previous studies 6,7.
In this study, the most common inaccurate preliminary
diagnosis was lipoma, possibly due to the subcutaneous
location and consistency of the lesions. All these data may
show that clinical observation has a limited contribution to
the final histopathological diagnosis of CSMTs.
Extremities have been reported to be a common site for
CSMTs 6,7. Our study showed a remarkably higher
rate of extremity involvement (71.9%) compared to the
relevant literature. The breast, back, face, vulva, and gluteal
region were the other locations in this study. There was
no statistically significant difference between the site of
involvement and tumor subtype, gender, age, and lesions
In this study, underrecognized histological aspects of
CSMTs such as epidermal features, pigmentary changes
and secondary alterations have been specifically addressed.
In our study, various degrees of epidermal hyperplasia
were present in all PLMs while only 2 ALMs showed mild
epidermal hyperplasia (p=0.052). In a study investigating
the histological features of PLMs, the authors identified
epidermal hyperplasia in 54.7 percent of the 53 lesions
included 12. We also identified epidermal basal
pigmentation in 87.5 percent of PLMs, while only two
ALMs and one of the LMSs showed this finding (p=0.045).
Malhotra et al. have also identified epidermal basal
pigmentation in 78.4 percent of the 37 lesions included
6. Along with the previous studies, our study showed that
epidermal hyperplasia and epidermal basal pigmentation
may be considered as remarkable clues to PLMs.
Secondary histopathological changes such as hyalinization,
myxoid changes, calcification and cystic degeneration in
CSMTs have rarely been addressed in the previous reports.
In the study of Ghanadan et al., hyalinization and myxoid
changes were detected in 75 percent of ALMs, while none of
the PLMs showed any secondary changes 7. Yokoyama et
al. have identified hyalinization in 76.9 percent of 13 genital
leiomyomas 13. In this study, secondary histological
changes were observed in 47.3 percent of ALMs, 12.5
percent of PLMs, and both of the LMSs (p=0.003). We
hypothesized that the vascular endothelial component in
ALM, which is a rich source of inflammatory mediators,
may cause a tendency for secondary changes 14. Duration
of the lesions, traumatization, and irritation may also be
associated with secondary changes.
In this study, the presence of chronic inflammatory cell
infiltration was detected in 21 percent of ALMs and 50
percent of PLMs (p=0.484), suggesting the possible role
of inflammation in the tumor pathogenesis. In the study of Raj et al., 86.7 percent of the cases also showed chronic
inflammatory infiltration 12.
We detected entrapped hair follicles and eccrine glands
in all PLMs while none of ALMs had these findings.
Ghanadan et al. identified entrapped hair follicles and
eccrine glands in 60 percent of 20 PLMs 7. It is clear that
the presence of entrapped hair follicles and eccrine glands
can be considered as a remarkable clue for PLMs.
In our study, the prominent histopathological features of
LMSs were large tumor sizes, ulceration, nuclear atypia,
necrosis and high count of mitosis including atypical ones.
The mean mitosis count was found to be lower than 1/10
HPF for benign CSMTs. Absence of ulceration, nuclear
atypia and necrosis were the other clues for a diagnosis
of benign CSMT. These features were in line with the
previously reported data 15. Unlike the previous studies,
however, hyaline degenerative changes were observed in
Our study has two main limitations. The first one is the
retrospective nature and the second one is the relatively
small number of cases included. The fact that the patients
do not apply to the clinicians because the lesion is
asymptomatic or that the clinicians tend to use conservative
methods instead of surgical excision may explain the small
number of cases included. However, given the paucity of
the studies on the subject in the relevant literature, we
believe that the present study may encourage prospective
studies with larger sample sizes.
In conclusion, we suggest that along with well-described
histomorphological findings of CSMTs, considering the
clinical features and less-defined histological characteristics
may increase the diagnostic accuracy. To the best of our
knowledge, this study represents the first original study
focusing on the cli
CONFLICT of INTEREST
The authors declare no conflict of interest.
No funding to declare.
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