Working Diagnosis:
Morel-Lavallée lesion of the left anterior thigh.

Treatment:
The patient was treated with Tubigrip® stockinette and cryotherapy. Consideration was given for both US-guided drainage and sclerodesis; however the relatively minor size of the fluid accumulation did not warrant this more invasive therapy.

Outcome:
Return to normal sporting activity with use of compression stocking to prevent fluid reaccumulation. Consideration given to drainage and sclerodesis if swelling or active range of motion worsen.

Author's Comments:
A Morel-Lavallée lesion of the distal anterior thigh is an uncommon diagnosis, especially with a low-energy mechanism of injury. Whether or not the adolescent's history of ALL in this case is relevant is unknown, and likely represents a red herring. While more commonly seen in professional athletes, management in non-elite athletes in typically conservative. The radiographic findings are unique and are presented with the case to highlight the appearance using different imaging modalities.

Editor's Comments:
Morel-Lavallee lesions are closed post-traumatic soft tissue shearing injuries that result in a degloving of the skin and subcutaneous tissues from the underlying muscle fascia. As this occurs, the local vasculature and lymphatics are disrupted causing blood and lymph to fill the potential space created by the injury. (5,6) When the lesion is not treated acutely, an inflammatory reaction follows that results in the formation of a fibrous capsule.(5, 14)

The lesions are most frequently reported following high velocity injuries to the pelvis or thigh, such as in motor vehicle accidents. However, they can also occur from low-velocity, crush injuries in sports such as football and wrestling. The most commonly reported areas of injury are the greater trochanter, thigh, pelvis, and knee. Less common locations are gluteal, lumbosacral, and abdominal, and lower leg. (17)

Patients typically complain of pain and a slowly progressive swelling that begins within hours or days of the injury. The lesion is easily overlooked in the setting of severe trauma, resulting in presentation for care months after injury. (7) On examination, there is a soft, fluctuant mass which may have decreased sensation due to cutaneous nerve shear injury. If large, the lesion may even cause skin necrosis. MRI is considered to be the imaging modality of choice for these lesions, as it can differentiate the lesion from a soft tissue sarcoma. (10) In addition, it can help define the lesion chronicity and type. There are six types of Morel-Lavallee lesions described in the literature. Reader is referred to the review article by Bonilla-Yoon, et al (2) for further details.

Ultrasound can also be used in the evaluation of Morel-Lavallee lesions, which will appear as non-specific fluid collections with mixed echogenicity. (3,4,11,12,16) Lesions will be compressible without flow on color Doppler. Injuries that are in the acute phase (< 1 month) will have a heterogeneous appearance, lobular shape, and irregular margins. Chronic lesions (>18 months) are reported as more homogeneous with smooth margins and a flat or fusiform shape. (11) With sonography, concomitant muscle contusion or laceration may also be apparent. (9) Ultrasound is the modality of choice for guided aspiration.

Treatment of Morel-Lavallee lesions can be challenging. If there is skin necrosis overlying the lesion, formal surgical debridement followed by wound VAC therapy is necessary. (13) However, the most appropriate approach for those with viable skin is more variable. Treatment has ranged from conservative management with observation and compression dressings, to aspiration, to aspiration with sclerodesis, to surgical resection, to even radical surgery. Sclerodesis with talc (8), ethanol (15) or doxycycline (1) is recommended for recurrent lesions following aspiration. A retrospective review of 87 Morel-Lavallee lesions was undertaken to determine the most appropriate therapy. In the study, patients who underwent aspiration with a volume of fluid aspirated of 50 ml or greater demonstrated an 83% recurrence rate versus a 23% recurrence rate for those with lesser volumes. As such, the investigators recommend that patients with large volume Morel-Lavallee lesions (>50 ml) should undergo surgical management. Those with lesser volumes may be treated conservatively with observation and compression dressings. (13) (Level III study)

In summary, Morel-Lavallee lesions are shearing, degloving injuries to the skin and subcutaneous tissues that result in a cystic mass of serosanginous fluid. MRI is the imaging modality of choice for differentiating the lesion from other diagnoses, while ultrasound is preferred for guided aspiration. If there is an aspirate greater than 50 ml, the patient should be referred for possible surgical intervention. With smaller aspirates, conservative management with compression dressings is recommended.

REFERENCES
1. Bansal A, Bhatia N, Singh A, Singh AK. Doxycycline sclerodesis as a treatment option for persistent Morel-Lavalle´e lesions. Injury. 2013; 44(1):66-69.
2. Bonilla-Yoon I, Masih S, Patel DB, White EA, Levine BD, et al. The Morel-Lavallee lesion: pathophysiology, clinical presentation, imaging features, and treatment options. Emerg Radiol 2014; 21:35-43.
3. Choudhary AK, Methratta S. Morel-Lavallee lesion of the thigh: characteristic findings on US. Pediatr Radiol 2010; 40(Suppl 1):S49
4. Goodman BS, Smith MT, Mallempati S, Nuthakki P. A comparison of ultrasound and magnetic resonance imaging findings of a Morel-Lavallee lesion of the knee. PM & R J Inj Funct Rehabil 2013; 5(1):70–73
5. Hak DJ, Olson SA, Matta JM. Diagnosis and management of closed internal degloving injuries associated with pelvic and acetabular fractures: theMorel-Lavallee lesion. J Trauma 1997; 42(6):1046–1051
6. Hudson DA, Knottenbelt JD, Krige JE. Closed degloving injuries: results following conservative surgery. Plast Reconstr Surg. 1992 ;89(5):853-855.
7. Hudson DA. Missed closed degloving injuries: late presentation as a contour deformity. Plast Reconstr Surg. 1996; 98(2):334-337.
8. Luria S, Applbaum Y,Weil Y, Liebergall M, Peyser A. Talc sclerodhesis of persistent Morel-Lavalle´e lesions (posttraumatic pseudocysts): case report of 4 patients. J Orthop Trauma. 2006; 20(6):435-438.
9. Mankad K, Hoey E, Grainger AJ, Barron DA. Trauma musculoskeletal ultrasound. Emerg Radiol 2008; 15(2):83–89
10. Mellado JM, Bencardino JT. Morel-Lavallee lesion: review with emphasis on MR imaging. Magn Reson Imaging Clin N Am 2005; 13(4):775–782
11. Mukherjee K, Perrin SM, Hughes PM. Morel-Lavallee lesion in an adolescent with ultrasound and MRI correlation. Skelet Radiol 2007; 36(Suppl 1):S43–S45
12. Neal C, Jacobson JA, Brandon C, Kalume-Brigido M, Morag Y, Girish G. Sonography of Morel-Lavallee lesions. J Am Inst Ultrasound Med 2008; 27(7):1077–1081
13. Nickerson TP, Zielinski MD, Jenkins DH, Schiller HJ. The Mayo Clinic experience with Morel-Lavallee lesions: establishment of a practice management guideline. Acute Care Surg 2014; 76:493-497.
14. Parra JA, FernandezMA, Encinas B, RicoM. Morel-Lavallee effusions in the thigh. Skelet Radiol 1997; 26(4):239–241
15. Penaud A, Quignon R, Danin A, Bahe L, Zakine G. Alcohol sclerodhesis: an innovative treatment for chronic Morel-Lavalle´e lesions. J Plast Reconstr Aesthet Surg. 2011;64(10):e262-e264.
16. Puig J, Pelaez I, Banos J, Balliu E, Casas M, Maroto A et al. Long-standing Morel-Lavallee lesion in the proximal thigh: ultrasound and MR findings with surgical and histopathological correlation. Australas Radiol 2006; 50(6):594–597
17. Vanhegan IS, Dala-Ali B, Verhelst L, Mallucci P, Haddad FS. The Morel-Lavallee lesion as a rare differential diagnosis for recalcitrant bursitis of the knee: case report and literature review. Case Rep Orthop 2012; doi:10.1155/2012/593193.

References:
1. Borrero CG, Maxwell N, Kavanagh E. MRI findings of prepatellar Morel-Lavallée effusions. Skeletal Radiology. 2008;37(5):451-455.
2. Goodman BS, Smith MT, Mallempati S, Nuthakki P. A comparison of ultrasound and magnetic resonance imaging findings of a Morel-Lavallee lesion of the knee. PM R. 2013;5(1):70-73.
3. Luria S, Yaakov A, Yoram W, Meir L, Peyser A. Talc sclerodhesis of persistent Morel-Lavallée lesions (posttraumatic pseudocysts): Case report of 4 patients. Journal of Orthopaedic Trauma. 2006;20(6):435-438.
4. Mukherjee K, Perrin SM, Hughes PM. Morel-Lavallee lesion in an adolescent with ultrasound and MRI correlation. Skeletal Radiology. 2007;36(SUPPL. 1):43-45.
5. Tejwani SG, Cohen SB, Bradley JP. Management of Morel-Lavallee lesion of the knee: Twenty-seven cases in the national football league. American Journal of Sports Medicine. 2007;35(7):1162-1167.

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