In this report, we presented a case of PF in the mandible in a child. PF is considered a subtype of NF and is far less commonly reported. Few studies have been published on NF and/or PF in children, and notably, the occurrence of mandibular NF and/or PF in children is extremely rare. Bemrich-Stolz et al. reported 18 cases of NF in pediatric patients over a 12-year period [9]. Among them, seven patients had NF in the head and neck but none in the mandible. Recently, it has been reported that in 15 children with NF in the head and neck, the most common location of NF was the maxillofacial region, followed by the scalp, forehead, and neck. Only one patient had NF in the mandible [4].
To the best of our knowledge, in pediatric population, only three mandibular PF patients, including our case, have appeared in the literature [1, 10]. All three patients had a similar clinical feature of rapidly growing painless swelling, leading to concerns for high-grade malignant neoplasms such as sarcoma. Hence, surgical excision was performed in all three cases. Therefore, verification of the diagnosis of PF before surgery is important; however, differentiating PF from neoplastic lesions by clinical examination alone is difficult.
The radiological (CT and MRI) findings of NF and/or PF are non-specific and variable. MRI of NF shows various signal intensities, probably because of the combination of variability in cellularity, amount of collagen, amount of cytoplasm and water content in the extracellular space, and vascularity in the individual lesion [6, 11]. The relationship between signal intensities on T2-weighted MRI and histological subtypes has been advocated [2, 11, 12]. In general, the signal intensity of the lesion with myxoid or cellular histology is higher than that of muscle on T2-weighted images, whereas lesions with fibrous histology present as a markedly hypointense signal compared with the surrounding muscles on all pulse sequences. The coexistence of abundant collagen and acellularity in the fibrous lesions leads to a reduction in signal intensity on T2-weighted images [11]. In this study, the signal intensity of the mass was isointense and hyperintense compared to that of muscles on T1-weighted and T2-weighted images, respectively, favoring the predominant myxoid or cellular nature of the lesion.
Dynamic contrast-enhanced MRI using gadolinium revealed increased heterogeneous enhancement. The time-intensity curves showed a gradual increment pattern in the central region of the mass and a pattern of rapid uptake followed by a gradual decrease in the peripheral region of the mass. The time-intensity curve pattern observed in the peripheral region of the mass is similar to that of malignant tumors; however, the gradual increment pattern in the central region of the mass was atypical for malignant tumors and favored benign lesions. Also, in the present case, the ADC of the lesion was suggestive of a benign etiology rather than a malignant etiology. ADC calculated from diffusion-weighted imaging using two b-values of 500 s/mm2 and 1000 s/mm2 was higher than the standard value for head and neck malignancies, such as squamous cell carcinoma and malignant lymphoma [13]. However, the significance of time-intensity curves and ADC in differentiating malignant tumors from benign lesions has not been fully elucidated and requires further examinations.
FDG-PET visualizes glucose metabolism and is widely used to differentiate between benign and malignant lesions, as well as to stage/restage various malignancies. In a number of cases, the degree of 18F-FDG accumulation is used to differentiate between malignant and benign lesions. However, numerous other benign conditions, such as abscess, pulmonary granuloma, tuberculosis, and sarcoidosis, may also present with increased 18F-FDG uptake [7, 8]; thus, the role of FDG-PET in distinguishing benign or non-neoplastic lesions from malignant lesions remains controversial. Some authors have described the efficacy of dual-time-point imaging, that is serial scanning at two different (early and delayed) uptake periods, for differentiating benign lesions from malignant lesions [14, 15]. In general, 18F-FDG accumulation in malignant lesions tends to increase over several hours. On the contrary, 18F-FDG uptake by benign lesions undergoes an early plateau, providing a potential means of differentiation [16]. In the present case, dual-time-point FDG-PET/CT showed decreased 18F-FDG accumulation on the delayed scan, which favored the benign etiology over the malignant one. To the best of our knowledge, no study has evaluated PF using dual-time-point FDG-PET/CT.
The diagnosis of PF is challenging; however, the radiological characteristics of the present case, such as the time-intensity curves and ADC of MRI and dual-time-point FDG-PET/CT findings, could have potential usefulness in differentiating PF from malignancy and, thus, in the diagnosis of PF.
Because the diagnosis of PF is difficult with clinical examination and imaging, histological examination is necessary to confirm the diagnosis. Histologically, PF shows features similar to NF. Allen identified four features that are common in nearly all cases of fasciitis: (1) presence of spindle-shaped fibroblasts that tend to be arranged in long fascicles, which are slightly curved, whorled, or S-shaped; (2) presence of small vascular clefts or slit-like spaces that often separate the fibroblasts; (3) extravasation of erythrocytes; and (4) presence of mucoid interstitial ground substance [2, 12, 17]. In addition to these four features, our case revealed that the presence of a hyperplastic periosteum with reactive ossification is an important feature of PF and can be used for the diagnosis of PF. Periosteal reactions were also observed in two other PFs that occurred in the pediatric mandible [1, 10]. In general, peripheral reactions of NF other than PF are not detected histologically. NF arising from subcutis and within muscle often extend between fat cells and muscle cells, respectively [17]. Contrast to the sarcomatous infiltrating appearance in them, PF is well-circumscribed from the overlying soft tissue, and possibly encapsulated. This phenomenon is due to reactive periosteal overgrowth with reactive bone formation [12]. The mechanism of periosteal hyperplasia and bone formation is unknown but may be related with the mediators secreted from the tumor cells and/or stimulus by external force.
Once the diagnosis of NF and/or PF has been made histologically, local excision is usually the appropriate treatment. After surgical excision, the prognosis of NF and/or PF is good and the recurrence is exceedingly rare [4, 11]. In fact, two pediatric patients with mandibular PF were reported to have no signs of mass recurrence at re-evaluation. However, no radiographic images of these two cases were provided. The present report is the first to describe the CT findings at 1.5 years after surgical excision of mandibular PF in a child. Neither radiographic nor clinical examinations demonstrated any signs of mass recurrence.
In conclusion, this article describes a rare case of PF originating from the periosteum of the mandible in an 11-year-old girl who exhibited clinical and radiographic features of a neoplastic disorder. The mass was surgically excised, and the diagnosis of PF was verified histologically. PF shares common clinical and radiographic features with neoplastic mandible tumors and is often misdiagnosed as a malignant tumor of the soft tissues. Incorrect diagnosis may lead to overtreatment, potentially causing disturbed orofacial development in children. In this article, we imply the potential usefulness of MRI findings (i.e., time-intensity curves and ADC) and dual-time-point FDG-PET/CT findings to differentiate PF from malignancy. Nevertheless, in contrast to neoplastic tumors, PF has a good prognosis after surgical excision. Therefore, PF should be included in the differential diagnosis when neoplastic lesions of the mandible are encountered.
