A painless swelling in the left thigh.
The patient presented with a history of a painless swelling in the left mid thigh, which had progressed slowly over several months.
An MRI scan was performed. The coronal T1-weighted image (Fig. 1) showed a 6cm lesion closely apposed to the cortex of the medial aspect of the mid femoral shaft on the left. Serpiginous low signal was seen within the lesion. These low signal areas were thought to represent calcification or ossification. Unfortunately the patient did not have a plain film, and therefore correlation is not available. The lesion returned intermediate signal on axial T2-weighted scans (Fig. 2), which again demonstrated serpiginous low signal areas and hyperostosis of the adjacent femoral cortex. There was uniform signal suppression on coronal STIR images (Fig. 3). These signal characteristics were similar to the adjacent subcutaneous fat. The findings were typical for a parosteal lipoma.
Parosteal lipomas are rare, benign neoplasms of mature adipose tissue, which adhere firmly to the periosteum of the underlying bone . They typically present as an enlarging, non-tender mass in a middle-aged patient. The femur is the commonest site of involvement (1).
The tumour is circumscribed by a thin fibrous capsule. It has a broad-based attachment to the underlying bone. The point of attachment to the bone consists of mature hyaline cartilage, with endochondral ossification, which extends into the soft-tissue mass. Peripherally, there are spicules of cancellous bone surrounded by mature adipose tissue (2).
The radiological appearances of parosteal lipoma are consistent with the pathological findings. On plain films, there is usually a well-circumscribed radiolucent mass adjacent to the cortex. The underlying cortex may be thinned due to pressure erosion, or, as in this case, thickened due to focal hyperostosis, with a bony excrescence marking the point of attachment (3).
On MRI, there is low signal on all pulse sequences at the site of attachment of the tumour, due to cortical bone. Hyaline cartilage adjacent to the osseous excrescence returns intermediate signal on T1- and high signal on T2-weighted images. Fibrous tissue and peripheral calcification return low signal on all sequences (4).
The main differential diagnosis for a parosteal lipoma, due to its osseous and cartilaginous components, is an osteochondroma. However, the presence of fat within the matrix of a lesion seen in the characteristic location allows a confident diagnosis to be made on the basis of the imaging findings. This precludes the need for a biopsy. However, these lesions require surgical excision, which can be complicated, as they are often strongly adherent to the underlying periosteum.
Parosteal lipoma
Patient Information: 49-year-old male, chief complaint: painless swelling of the left thigh.
Based on the provided MRI images and the patient’s clinical presentation, a lesion primarily composed of fat density is observed within the soft tissue of the left thigh, with well-defined margins. The lesion is closely attached to the cortical bone, and a protruding structure connected to the bone is noted locally. Specific findings are as follows:
Based on the imaging findings and patient history, the following considerations should be included in the differential diagnosis:
Considering the patient’s age, the clinical course (painless, gradually enlarging mass in the buttock/thigh area), and the imaging characteristics demonstrating mature adipose tissue, close apposition to the cortical bone, and associated cartilaginous or osseous overgrowth, the most likely diagnosis is:
Parosteal Lipoma.
In most cases, typical imaging features allow a relatively confident diagnosis. If there are special concerns or the need for preoperative evaluation, further imaging (such as CT) or histopathological biopsy may be considered.
After surgery or upon diagnosis, rehabilitation and exercise should follow a gradual, individualized approach:
If the patient has other underlying conditions (e.g., osteoporosis, compromised cardiopulmonary function), special precautions should be taken, and exercise tolerance should be assessed beforehand. Ongoing communication with professionals is crucial to adjust exercise programs according to the recovery process.
Disclaimer:
This report is based solely on the provided imaging and clinical information for reference purposes and does not replace an in-person consultation or professional medical opinion. If there are any questions or discomfort, please consult a specialist promptly.
Parosteal lipoma
