Musculoskeletal systemCase Type
Dr Juvaina P, Dr Sandeep Govindan Prasad, Dr Devarajan E, Dr Rinu Susan Thomas, Dr Lin VarghesePatient
55 years, male
A 55-year-old male patient presented with swelling in the lateral aspect of right thigh since 1 month following a history of fall on right thigh 5 months back. There was no history of pain at the site or fever at present.
USG examination showed an anechoic thick-walled lesion (Fig 1 ) with fluid debris level ( arrow in Fig 2 ) and a mobile hyperechoic structure suggestive of a fat globule ( arrow in Fig 3) in subcutaneous plane in the anterolateral aspect of right thigh. MR imaging showed a well-defined oval-shaped altered signal intensity lesion adherent to the deep fascia overlying the greater trochanter. The lesion (arrow) appeared hypointense in axial T1WI with hyperintense focus medially (Fig 4), hyperintense in coronal STIR image with the small medial focus being completely suppressed (green circle in Fig 5), and hyperintense in axial T2WI with fluid levels ( Fig 6). Axial T1WI post gadolinium contrast-enhanced image showed peripheral rim enhancement of the lesion with enhancement of adjacent soft tissue posteriorly (Fig 7). Coronal T2* GRE images showed blooming within the lesion suggestive of haemorrhage (Fig 8).
First described by the French physician, Victor-Auguste-François Morel-Lavallée in 1863, it is a type of closed traumatic soft-tissue degloving injury . A consequence of high energy trauma and shear stress, it occurs due to the separation of hypodermis from the underlying fascia disrupting perforating vascular and lymphatic structures and creating a collection of blood, serosanguinous fluid, and necrotic fat with a tendency to expand and grow.  Gross pathological examination reveals a well-defined collection with an outer pseudo capsule formation in later stages filled with blood clots, fibrin, necrotic and normal fat globules with secondary microbial infection in up to 46% patients .
The most common site of involvement is the greater trochanter as a result of its large surface area, overlying mobile skin and large underlying dense capillary network with other common sites being thigh, pelvis and knee . The lesion is notorious for its under detection in early stages due to late superficial skin discolouration following the traumatic episode . Local examination findings include ecchymosis, soft tissue swelling, fluctuance, skin hypermobility, and associated pelvic and acetabular fractures.
Ultrasound examination reveals large well defined, oval or fusiform, compressible lesions with partial/complete septae, fluid levels, absent internal vascularity and a variable internal echogenicity within depending on the age of hematoma . Though not pathognomic, rounded mobile hyperechoic foci within the lesion suggestive of sheared, disrupted fat globules is fairly specific to this condition . Magnetic resonance imaging (MRI) is the investigation of choice and can reveal six types based on signal intensity (SI) characteristics and age of the lesion . Type 1 lesions are most common and they are seromas in nature, type 3 is a chronic organizing hematoma, whereas type 2 lesion is a subacute hematoma as in our case which shows hyperintense SI on T1 and T2WI, internal inhomogeneity caused by entrapped fat globules, internal septations, fluid-fluid levels, thick peripheral capsule with close abutment of fascial planes being a common feature of all subtypes. The last three subtypes are rare, longstanding and atypical lesions demonstrating perifascial dissection and fatty layer lacerations .
This lesion can be managed conservatively, by percutaneous drainage, or open debridement and irrigation as was done in our case . To the treating orthopedician, this is an important diagnosis as it is a significant cause of underlying peri operative infection, with early USG evaluation by the radiologist assuming critical importance .
Written informed patient consent for publication has been obtained.
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