Thigh Mass in a 73-Year-Old Woman

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LEARNING OBJECTIVESOn completion of this activity, the reader should be able to:identify radiographic features that suggest the presence of an adipose neoplasm;describe the histologic differences between adipose neoplasms; andselect the appropriate treatment for the adipose lesion.HISTORY AND PHYSICAL EXAMINATIONA 73-year-old female was referred to the orthopaedic service with a history of a large right thigh mass first noticed 2 months previously. The mass was nonpainful, but was associated with a feeling of heaviness and pressure, especially with standing for long periods of time. The patient denied numbness, parasthesias, and weakness of the right lower extremity. There was no history of trauma and no history suggestive of infection. The patient did not report other masses. The patient’s medical history included a small, possibly benign soft tissue mass excised from the same area 3 years previously. No further information concerning this mass was available. Other past medical history and family history were noncontributory.On physical examination, the patient had a normal gait pattern. A 20 × 10 cm deep, soft, nontender mass was palpated on the proximal ⅔ of the anterolateral right thigh. There was no warmth, erythema, or surrounding edema. A 3-cm linear scar that had healed by primary intention was observed superficial to the mass. Range of motion, strength, and neurovascular examination were normal for both lower extremities. No other masses were palpated on general exam, and there was no considerable lymphadenopathy. The rest of the physical examination was normal.Anteroposterior and lateral plain radiographs, a CT scan, and MR imaging scans of the right leg obtained 2 weeks before referral to the authors’ institution are shown in Figures 1, 2, and 3. Based on the history, physical examination, and imaging studies, what is the differential diagnosis?IMAGING INTERPERETATIONPlain radiographs (Fig 1) of the right thigh showed a large, lucent lesion in the soft tissue of the right thigh laterally. No bony abnormalities were observed. An unenhanced CT image (Fig 2) of the right thigh showed a well-defined hypodense mass in the vastus lateralis muscle measuring −100 to −127 Hounsfield Units (HU). The mass contained an ill-defined area with a slightly increased density laterally (Fig 2, arrow). A T1-weighted (TR=600/TE=10) unenhanced coronal MR image (Fig 3A) and a STIR (TR=5866/TR=32.6/TI=150) coronal MR scan (Fig 3B) showed a 20 cm × 8.5 cm × 5.3 cm mass that was hyperintense on the T1-weighted images and suppressed on the STIR sequences almost entirely, with small foci of hypointensity in the mass superiorly on the T1-weighted scans (Fig 3, arrow), which became hyperintense on the STIR images (Fig 3, arrow).DIFFERENTIAL DIAGNOSISLipomaAtypical lipomaLiposarcomaHibernomaIntramuscular myxomaThe mass was completely excised without complications and was sent for routine histologic analysis. Based on the history, physical examination, imaging studies, and histologic picture, what is the diagnosis and how should the patient be treated?See page 269 for diagnosis and treatment.Continuation of ORP conference from page 268.HISTOLOGY INTERPRETATIONThe gross specimen consisted of multiple fragments of soft, yellow, lobulated tissue with admixed white fibrous tissue measuring 19.0 × 8.0 × 4.8 cm in aggregate.

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