Case: A 43-year-old postal worker presents on August 2, 2013 with a 3-month history of tingling and shooting pain on the anterolateral aspect of her left leg 2 cm above the ankle. There is no history of trauma.
Location: anterolateral left leg
Quality: tingling, hyperesthesia, pins and needles, sharp pain
Onset: 3 months ago
Course: worsening; the episodes are more frequent
Timing: sporadic episodes
Inciting event: none
Past treatment: none
Review of systems: unremarkable
Past medical history: healthy
Vascular: Pulses 2/4 DP and PT (B/L); capillary fill time less than 3 seconds b/l ; no edema; color normal; temperature normal
Skin: slight xerosis of plantar feet; no lesions; nails normal in appearance
Musculoskeletal: all muscles 5/5 B/L; joints normal ROM with no crepitus or pain; no masses noted
Neuro: Tinel sign noted over superficial peroneal nerve left . This is at the anterolateral left leg above the ankle. No masses are appreciated. Overlying skin normal. No erythema, calor or edema. Hyperesthesia is noted with light touch.
no tinel sign: tarsal tunnel B/L
no tinel sign: common peroneal nerve B/L
no tinel sign: deep peroneal nerve B/L
neuro exam: unremarkable
Ankle X-rays: (AP, mortise and lateral) unremarkable
Diagnostic ultrasound: Hypoechoic mass noted anterolateral left leg. It measures 5.8 mm x 2.0 mm on transverse and sagittal views. There is a well delineated border. The mass is oval to fusiform in shape. Internal light echogenic material is seen within the mass when gain was slightly increased. The mass is only slightly compressible with the probe. Provocation sign elicited with probe pressure. Scanning the leg proximal and distal showed absence of the lesion. There was no critical edge shadowing. Posterior acoustic enhancement was minimal. Power Doppler was employed and increase signal noted around the lesion was abundantly present, but only minimal signals at pinpoint locations within the lesion were seen. Color Doppler showed the same, but with possible small vessels associated with the lesion. Otherwise, the lesion was mainly avascular. Clearly on transverse scan (short axis), the superficial peroneal nerve is seen in typical honeycomb appearance, but is more fusiform than typically seen. It is deep to the lesion, which is compressing the nerve. The lesion does not show fascicular internal echotexture, but I cannot determine if mass is completely separate from the nerve. I was not able to appreciate the nerve well enough on the long axis. Surrounding tissue planes were “disturbed” on the long axis, possibly from the mass.
What would you suggest as a differential diagnosis for this mass?
Taking into consideration some of the sonographic characteristics on the lesion, what is the most likely diagnosis?
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