Clinical History
A 5-year-old boy came to the emergency department for knee pain and functional impairment of the lower limb of recent onset. At first, because of frequent reflected symptoms originating from the hip, both an ultrasonography and radiography of the right hip joint were performed with negative results.
Imaging Findings
The AP radiograph of the femur showed an osteolytic lesion associated with periosteal fusiform reaction in the diaphysis (Fig. 1a). Therefore, we decided to carry out both an MRI study of the right femur and a whole-body MRI study (STIR and T1W images) to exclude a multifocal skeletal involvement. The MR examination of the femoral region (Fig. 1b, 1c) showed that the focal lesion in the right femoral diaphyseal had a marked contrast enhancement (CE), associated with an extensive CE within the cancellous bone and adjacent soft tissue (Fig. 1c); MR confirmed also a marked fusiform homogeneous periosteal reaction.
Discussion
EG is part of a family of diseases (also nominated Langerhans cell histiocytosis (LCH) or histiocytosis X) with aetiology and pathophysiology still undefined, whose common denominator is the Langerhans cell (cell of mononuclear bone marrow-derived dendritic type with peculiar ultrastructural and immunohistochemical features.) [1]
The term eosinophilic granuloma refers to a monostatic benign LCH, and is rather considered a disorder of immunoregulation than a neoplastic process. [2]
From the radiological point of view the lesion at the level of the shaft of long bones is presented as destructive osteolytic lesion with margins more or less defined, with associated periosteal reaction of lamellar type. These features can mimic those of a malignant tumour, such as Ewing's sarcoma and lymphoma [2]. The radiological appearance of the lesion can be time-varying depending on the developmental stage with a prevalence of sclerosis and periosteal reaction in later stages. Even the appearance of the lesion on MRI, which usually involves an extensive alteration of signal with contrast enhancement of the cancellous bone and adjacent soft tissues, can simulate that of an aggressive lesion such as Ewing's sarcoma and osteomyelitis [1].
Differential Diagnosis List
Eosinophilic granuloma (EG).
Lymphoma
Ewing sarcoma
Osteomyelitis
Final Diagnosis
Eosinophilic granuloma (EG).
