Intraosseous lipoma of the talus

Clinical History

In January 2013, this patient presented with pain and swelling in the left ankle after a twisting injury six days ago. Her bloods were normal.

Imaging Findings

Figure 1. AP radio-graph shows a well-corticated 14mm round-to-ovoid lucent lesion within the head/neck of the talus. No fracture is demonstrated. No cortical breach or periosteal reaction is demonstrated.

Figure 2. Lateral radio-graph shows a well-corticated 14mm round-to-ovoid lucent lesion within the head/neck of the talus. The lesion does not reach the articular surface of the talus, excluding an OCD. No fracture is demonstrated. No cortical breach or periosteal reaction is demonstrated.


Figure 3. MRI TI Sag sequences shows a well defined ovoid lesion within the talus. The lesion shows a high signal on T1 sequences.


Figure 4. MRI PD FS sequence shows signal loss within the lesion, indicating that the lesion is of fat density, hence narrowing the differential.

Discussion

Differential Diagnosis:

Based on Radiographs: (FOG-MACHINES)...there is a wide differential for solitary bone lesions.

Fibrous Dysplasia
Osteoblastoma
Giant Cell Tumour
Metastasis / Myeloma
Aneurysmal Bone Cyst
Chondroblastoma / Chondromyxoid Fibroma
Hyperparathyroidism (brown tumours) / Haemangioma
Infection
Non-ossifying Fibroma
Eosinophilic Granuloma / Enchondroma
Solitary Bone Cyst


Given the appearance and location of the lesion, more realistic possibilities include:
Simple Bone Cyst
Fibrous Dysplasia
Enchondroma
Chondromyxoid Fibroma


Based on MRI scans:
Lipoma
Liposarcoma.


This lesion is an intra-osseous lipoma. These are rare, benign tumours with an incidence of <0.1% per year. They are usually asymptomatic and diagnosed incidentally. Most patients are middle aged with a male predominance. The calcaneum is the most commonly affected site in the foot. Cases within the talus are rare.

Intraosseous lipomas have 3 stages: (1) Purely radio-lucent with cortical expansion. (2) Similar radio-graphic appearance but contains localised calcification. (3) Lesion shows ossification around the calcified fat of the outer rim.

Teaching points:

There is a wide differential for solitary bone lesions, however some of them may have distinguishing features e.g. an associated clinical history or associated clinical finding which helps to narrow the diagnosis, such as a raised white cell count and pyrexia for infection. Some of the lesions are also more common at certain sites e.g. a chondroblastoma more commonly occurs in the epiphysis. Others have distinctive features e.g. fibrous dysplasia has a ground glass appearance. Certain tumours are also more typical in certain age groups e.g. a chondroblastoma is more common in the 1st-2nd decade. Intra-osseous lipomas can also mimic an OCD when occurring close/adjacent to the articular surface of the talus.

Further investigation with MRI is sometimes necessary to narrow the differential diagnosis. The loss of signal on the STIR sequence indicated that the lesion contained fat. The most common fat based lesion occurring in the calcaneum is a lipoma. These are rare within the talus but cases have been reported. (Please see references). The lack of aggressive features on both radiographs and MRI makes this lesion less likely to represent a liposarcoma, however malignant transformation of a lipoma to a liposarcoma has been reported and repeat imaging is advised if the patient develops new clinical symptoms.

Differential Diagnosis List

Final Diagnosis

Intraosseous lipoma of the talus

URL:	https://eurorad.org/case/11039
DOI:	10.1594/EURORAD/CASE.11039
ISSN:	1563-4086