A 50-year-old man presented with increase in the volume of his right thigh since 4 years. He also complained of recurrent pain and heaviness in his right thigh. He was referred for imaging to our department and subsequently underwent surgical resection of a mass.
Radiograph of thigh (Figure 1) showed a well defined low density mass with associated bony excrescence originating from the anterior femoral cortex.
Ultrasonography (Figure 2) showed a well defined elongated hypoechoic mass located deep to the vastus intermedius muscle. A broad based bony projection was seen posterior to mass with irregular outline merging with the external cortex of femur.
CT (Figure 3) revealed a well defined fat density mass in anterior thigh with adjacent bony excrescence along the anterior femoral cortex. There was no continuity of the bony excrescence with medulla of the femur, differentiating it from an osteochondroma.
MRI (Figures 4 and 5) confirmed a lobulated lesion measuring 5.2 x 2.4 x 8.6cm(ML x AP x SI). The lesion was hyperintense on T1- and T2-Weighted images (WI) and suppressed on STIR and fat saturated T2-WI.Thin intralesional septations within showed subtle enhancement. The bony excrescence attached to anterior femoral cortex appeared hypointense on all pulse sequences.
Lipomas are benign tumours of mature adipose tissue without cellular atypia. Parosteal lipoma is benign tumour of adipose tissue intimately associated with periosteum of bone. Parosteal lipomas share histopathologic features with commonly occurring soft-tissue lipomas, and cytogenetic evidence suggests common histopathogenesis [1].
The parosteal lipoma is rare tumour accounting for 0.3% of all lipomas [2].It affects adults with age 40 -60 years and presents with palpable mass or mild-intensity pain.
Paraosteal lipomas exhibit distinctive radiographic features that helps in diagnosis. These are fat containing lesions adjacent to the cortical bone often associated with reactive changes.These changes include bone deformity, cortical erosion, and overproduction of the cortical bone (hyperostosis).More than half are associated with hyperostosis.The most frequently affected sites are the diaphysis and metaphyseal regions of long bones [3].
MRI is the imaging modality of choice. It mainly reveals fat signal intensity on all sequences. However low-signal-intensity strands on T1W which appear as high signal intensity on STIR/T2 fat saturated images correspond to fibrovascular strands that are commonly found in lipomatous lesions [4]. Cartilaginous components reveal intermediate signal on T1-weighted and high signal on T2-weighted images. Bony protruberance appears as hypointense signal on all sequences.
At gross examination, these have mature fat identical to soft-tissue lipomas. Cartilage, osteoid metaplasia, and areas of osseous excrescences or cortical thickening extend from bone surface to the lesion. These osseous excrescences do not show cortical or medullary continuity with the adjacent bone. The cartilage and osteoid metaplasia typically occur adjacent to the osseous excrescences.
Bone destruction is typically absent in paraosteal lipomas. Osseous excrescences may mimic osteochondromas, although osteochondromas characteristically are continuous with medullary marrow of the underlying bone. This tumour should also be differentiated from liposarcoma. Parosteal lipomas show thin fibrous septa which show either no or minmal enhancement as compared to liposarcomas which have thickened or nodular fibrous septae showing moderate to intense enhancement. "Associated nonadipose soft tissue masses, prominent foci of high T2 signal, and prominent areas of enhancement also favour liposarcoma.[5]"
Parosteal lipomas commonly cause nerve compression with motor and/or sensory function deficit. Nerve compression is most common with parosteal lipomas of the proximal forearm which can ultimately progress to muscle atrophy. MRI initially shows muscle edema with hyperintense signal on T2W images which can progress to muscle atrophy (decrease in volume) and/or fatty infiltration which has high-intensity linear streaks of fat within muscle , best seen on T1W images.
Treatment of parosteal lipoma is complete surgical resection.
Parosteal Lipoma
Based on the provided X-ray, CT, and MRI images, a well-defined fat density/signal lesion is visible near the cortex of the right femur, closely attached to the periosteum. Some images show mild thickening or protrusion of the cortical surface without obvious cortical destruction or continuity changes in the medullary cavity. In the MRI sequences, the lesion primarily exhibits fat signals (high signal on T1-weighted images, high signal on T2-weighted images), with a small amount of fibrous tissue or septations appearing as low or slightly high signals. Overall, this presentation is consistent with dense fatty tissue in close proximity to the periosteum.
1. Parosteal Lipoma: Closely adhered to the periosteum, often accompanied by periosteal reaction or cortical thickening, without obvious cortical or marrow destruction, and predominantly shows fat signal. This is an important consideration.
2. Liposarcoma: Liposarcoma commonly occurs in middle-aged or older adults. If the lesion has thick, well-defined septations or a notable enhancing soft tissue component, liposarcoma should be considered.
3. Common Soft-Tissue Lipoma: Usually located in superficial or deep soft tissue. If it is not intimately associated with bone, a typical soft-tissue lipoma is more likely. In this case, because it is tightly connected to the periosteum, the relatively less common entity of parosteal lipoma needs to be carefully considered.
4. Osteochondroma: If the cortical bone protrudes outward and is continuous with the medullary canal, osteochondroma should be considered. However, since no continuity with the medullary canal is observed here, the findings are more consistent with a parosteal lipoma.
Taking into account the patient’s age (50 years old, which falls within the common range of 40–60 years), the long-standing mass in the right thigh over several years, and the imaging features (abundant fatty components, periosteal attachment, local cortical thickening without erosive changes), along with surgical and pathological findings, the diagnosis is confirmed as: Parosteal Lipoma.
If further clarification on the nature of the lesion is needed, pathological diagnosis and follow-up imaging may be considered. However, based on the current information, this diagnosis is most reliable.
Treatment Strategy:
1. Surgical Treatment: For parosteal lipomas that are large in size, symptomatic, or potentially compressing adjacent nerves or vessels, complete surgical excision is the primary treatment. Care should be taken to protect nearby nerve and vascular structures during surgery.
2. Follow-Up Observation: If the lesion is small and asymptomatic, periodic imaging follow-up may be considered to monitor changes in the lesion and surrounding tissues.
Rehabilitation/Exercise Prescription Suggestions:
1. Early Postoperative Phase:
- Focus on protected weight-bearing and basic functional training. During the first 1–2 weeks post-surgery, emphasize passive joint mobility and strength maintenance exercises, such as ankle pump exercises and isometric quadriceps contractions. Avoid strenuous activities.
- Conduct mild activity 2–3 times daily, each session lasting 5–10 minutes, gradually increasing the range of motion.
2. Intermediate Postoperative Phase (approximately 3–6 weeks after surgery):
- With medical clearance, gradually increase joint mobility exercises and introduce light resistance training (e.g., using resistance bands for quadriceps and hamstring strengthening).
- Exercise 3–4 times per week with moderate intensity, each session about 15–20 minutes, with appropriate rest between sets.
3. Late Postoperative Phase and Functional Recovery (after 6 weeks):
- Under the guidance of orthopedic surgeons and rehabilitation specialists, progressively transition to full weight-bearing and walking exercises. If necessary, use assistive devices (e.g., cane or walker) temporarily.
- Incorporate low-impact aerobic exercises (such as stationary cycling or swimming) 3–5 times a week for 20–30 minutes at moderate to low intensity.
- If there are no concerns regarding bone fragility, gradually increase resistance training (e.g., light dumbbells or heavier resistance bands). Monitor the affected limb closely when progressing in intensity.
Additional Considerations:
- If the patient has other comorbidities (such as diabetes or poor cardiopulmonary function), further individual adjustments to the training intensity and methods are necessary.
- In the event of significant pain, discomfort, or swelling, discontinue exercises and consult healthcare professionals promptly for evaluation.
Disclaimer:
This report is a reference analysis based on the current imaging data and clinical information. It does not replace an in-person consultation or advice from a professional physician. The specific treatment plan must be determined comprehensively, considering the patient’s actual condition and a doctor’s clinical assessment.
Parosteal Lipoma
