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.