Discussion
The present study described the findings of a Japanese case of SCL and
reviewed a Japanese case series of SCL, which were described by
researchers in various medical departments in a cross-sectional manner,
including orthopedics, plastic surgery, dentistry, otorhinolaryngology,
radiology, respiratory medicine, pathology, urology, surgery, and
dermatology. The results obtained suggest that SCL continuously grows,
and its imaging findings may become indistinguishable from those of
malignant soft tissue tumors over the long period from its onset.
Previous studies reported that the peak age of onset of SCL was between
45 and 65 years [1, 2]. These findings are consistent with the
present results, showing an average age of 59.2 years. SCL commonly
occurs in subcutaneous tissue in the nuchal region, shoulder, and back
[1]. In addition to these findings, the present study indicated the
oral cavity and lower extremities as sites predisposed to developing
SCL, at least in Japanese patients.
According to the classification in the World Health Organization,
lipomatous tumors are classified based on the prognosis of patients.
SCL, an atypical lipomatous tumor, and liposarcoma are regarded as
benign, intermediate malignant, and malignant lipomatous tumors,
respectively [63]. Previous findings and the present results
indicate that SCL often shows heterogeneity and enhancement in imaging
examinations, suggesting malignancy in contrast to banal lipoma. An
imaging examination was not useful for reaching a diagnosis in the
present case, which was indistinguishable from malignant lipomatous
tumors because of its heterogeneity. Therefore, the definite diagnosis
of SCL required a histopathological examination.
Banal lipoma does not show a significant sex difference [64]. In
contrast, previous findings and the present results indicated
significant sex differences in SCL. Furthermore, the present study
demonstrated that SCL was approximately 4-fold more common in males than
in females, which was consistent with previous findings, showing the
male predominance of SCL [65]. The present study
also showed that tumors were more likely to develop at a significantly
older age in Japanese males than in Japanese females. Furthermore, the
site of occurrence of SCL significantly differed between the sexes. The
most common site of occurrence was the lower extremities in women (7/16
cases), and the neck in men (25/68 cases), which may be attributed to
sex hormones; however, the underlying mechanisms remain unknown.
The present study revealed the clinical importance of the period from
perception of the tumor to the first hospital visit. The results
obtained showed that i) the
period from perception to the first hospital visit positively correlated
with the maximum gross tumor diameter, and ii) the period from
perception to the first hospital visit was significantly longer in
patients with enhancement than in those without. On the other hand,
statistical analyses failed to show that the period from perception to
the first hospital visit was significantly longer in patients with tumor
heterogeneity on images than in those without. This may be due to a
delay in perception of the tumor in many patients, which also led to an
underestimation of the period from the onset of the tumor to the first
hospital visit. In the present case, the 7-cm tumor was only perceived a
few days before the first hospital visit.
In the present study, a correlation was observed between enhancement and
the period from perception to the first hospital visit, but not between
the period and heterogeneity referring to structures with different
densities/signal intensities regardless of the administration of a
contrast agent. Thus, studies reporting heterogeneity may have been
performed without a contrast agent, which may explain the higher
sensitivity in the detection of enhancement than heterogeneity among the
reported cases.
There are a number of limitations that need to be addressed. The present
study was conducted to review various case reports from multiple
institutes. Therefore, the quality of imaging examinations was not
standardized. Furthermore, there was a lack of relevant clinical data in
some case reports, which may have affected the reliability of the
statistical analysis.