Abstract:

Atypical lipomatous tumor （ALT） is a rare soft tissue sarcoma originating from adipocytic tissue. The clinical manifestations， imaging findings， and pathological examinations of one patient with ALT in the lower extremity were reported to provide reference for the clinical diagnosis and treatment of this disease. The patient was a 64-year-old male who was admitted due to a mass in the left thigh with swelling and pain for 5 years. The physical examination results showed a subcutaneous mass was palpable on the medial side of the left thigh， soft in texture， demonstrating good mobility and positive tenderness.The magnetic resonance imaging （MRI） non-contrast scan showed a well-defined lesion with an intact capsule. The lesion presented high signal intensity on T1-weighted image（T1WI）， similar to subcutaneous fat signal； on T2-weighted image （T2WI）-Ideal in-phase images， the lesion showed high signal， while water images showed low signal， with multiple high-signal foci inside. On T2WI fat-suppression sequence， a low-signal mass was observed with multiple patchy high signals inside.Three days after admission， the patient underwent lesion resection. Intraoperatively， the tumor was located within the fascia， between the medial quadriceps muscles， presenting as lipomatous tissue with an intact capsule， mildly adherent to surrounding tissue， and with partial muscle invasion. The mass and invaded muscle were completely excised. The postoperative pathological examination results revealed a gray-yellow nodule measuring 16.0 cm×10.0 cm×4.0 cm， with a smooth surface and intact capsule. The cut surface was gray-yellow， fatty-like， and soft in texture. Additional gray-yellow tissue fragments were found， with a total volume of 5.0 cm×4.0 cm×1.2 cm， exhibiting a gray-brown cut surface with moderate texture. Under microscope， the lesion consisted mainly of relatively mature adipose tissue. Enlarged and hyperchromatic nuclei were observed， with scattered mononuclear or multinuclear atypical stromal cells. Fibrous septa contained variable numbers of univacuolated or multivacuolated lipoblasts. The immunohistochemistry results showed positivity for cyclin-dependent kinase 4 （CDK4） and murine double minute 2（MDM2）. The fluorescence in situ hybridization （FISH） results demonstrated MDM2 gene amplification in tumor cells. The pathological diagnosis was ALT of the left lower extremity. At 6-month follow-up after operation， no tumor recurrence was observed. The preoperative MRI detection may provide effective evidence for the diagnosis of ALT， while postoperative pathological examination can confirm the diagnosis and help evaluate the prognosis of the patients.

Key words: Lower limb, Atypical lipomatous tumor, Adipocyte, Prognosis, Murine double minute 2