Pain and swelling in the right gluteal region.
The patient presented with a six-month history of a swelling in the right gluteal region. Physical examination findings were otherwise normal. Laboratory findings were unremarkable.
MR imaging showed a large soft tissue mass that extended from the gluteal region to the pelvic area at the piriform muscle level. The tumour had inhomogeneous high signal intensity on T1-weighted and fat-supressed images (Figs 1,2).
The tumour was diagnosed as lipoblastomatosis after an incisional biopsy and thereafter an operation was performed with the aim of complete resection. There was no evidence of recurrence over the ensuing year (Fig. 3).
Lipoblastomatosis (LBM) is a rare, benign mesenchymal tumour that contains mature embryonic fat and was first described by Vellios in 1958. It occurs mostly in infants and children and is more often found in the extremities, mediastinum, neck and axillae. In Chung and Enzinger's series 88% occured before the age of 3 years. LBM constitutes 3% of tumours arising from fat cells in infants. The male:female ratio is 3:1. The tumour is generally asymptomatic and non-tender. LBM has two forms – a diffuse infiltrating variety and a well-circumscribed non-infiltrating type described as a lipoblastoma. LBM is more uncommon (1). It infiltrates along muscle planes without deep muscle invasion (2). The axillae, mediastinum, retroperitoneum and prevertebral space are the most common sites for LBM because lipoblasts, the embryonic fat-cell precursors of the tumour, are still normally found after birth in these locations (1). The tumour may have a rapid rate of growth. Calcification has never been reported.
Ultrastructural studies in LBM show a great variation in its cellular composition. It is characterised pathologically by lobules of mature lipocytes and immature lipoblasts separated by thin fibrous septae. Associated eosinophylic myxocollagenous stromal tissue is often seen (3,4). Due to this histological combination, LBM shows inhomogeneous signal intensity on all pulse sequences with MRI.
MRI is important for both definition and staging of the soft tissue tumour. Spin echo T1- and T2-weighted images are sufficient in most cases. Fat suppression images add additional information in fatty tumours. In general a fatty tumour has findings similar to those of subcutaneous fat on the various MRI sequences. In LBM fat-supression sequences are useful. The persistence of high signal in a lipomatous tumour on fat-supression sequences reflects the histological predominance of lipoblasts and myxocollagenous stromal cells and may be the most important MRI finding for differentiation of this tumour in the paediatric age group (5).
The differential diagnosis includes adipose soft tissue tumours relevant to the age of the patient and the location of the tumour. Liposarcoma is extremely rare in patients under 10 years of age. Diffuse lipomas or intramuscular lipomas show diffuse proliferation of mature adipose tissue with an irregular lobular arrangement and absence of lipoblasts and malignant characteristics (2,4).
In treatment, complete excision with a surrounding margin of normal tissue is advisible if possible (1). The reccurence rate is reported as between 14% and 25%. Metastasis does not occur in this malignant-appearing but histologically benign tumour (2).
Lipoblastomatosis
Based on the provided MRI images, a relatively large soft tissue mass is observed in the right buttock region, appearing lobulated or septated. On T1-weighted images, the lesion in certain areas shows signal intensity similar to subcutaneous fat, but in other areas, slightly heterogeneous mixed signals are visible. On T2-weighted images and fat-suppression sequences, the signal is also uneven, and some regions still display relatively high signals. This suggests a possible mixture of fatty components and myxoid stroma or immature adipocytes. The mass has a relatively clear margin but shows a diffuse infiltrative tendency along muscle planes, with no evident bone infiltration or destruction.
Considering the patient's age (2 years), clinical presentation (buttock mass, pain, and swelling), and imaging findings indicating predominantly fatty components with heterogeneous signals, the following potential diagnoses are considered:
Taking into account the child's age, symptoms, imaging characteristics, and the presence of multiple fat-like components possibly containing immature adipocytes, the most likely diagnosis is:
Lipoblastoma / Lipoblastomatosis.
If there is still uncertainty, pathological biopsy or surgical excision followed by histological examination can help confirm the diagnosis. Literature suggests that after complete resection, the prognosis is good, and distant metastases are extremely rare.
After surgery or other treatments, an individualized rehabilitation training plan should be developed according to the child's recovery and local tissue status. Below is a brief example based on the FITT-VP principle:
Disclaimer:
This report provides a reference analysis based on current imaging and clinical data, and does not replace in-person consultation or professional medical advice. Specific diagnosis and treatment plans still require the patient’s complete medical history, physical examination, pathology, and subsequent imaging follow-up, formulated by a professional medical team. If you have further questions or if conditions change, please promptly seek help from a physician or the relevant specialty.
Lipoblastomatosis
