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Original Report |
1 Institut de Diagnòstic per la Imatge, Hospital Universitari de
Tarragona Joan XXIII, Carrer Doctor Mallafrè Guasch 4, Tarragona 43007,
Spain.
2 Servei de Radiologia, Pius Hospital de Valls, Tarragona, Spain.
3 Servei de Anatomia Patològica, Hospital Universitari de Tarragona Joan
XXIII, Tarragona, Spain.
Received May 29, 2003;
accepted after revision November 10, 2003.
Address correspondence to J. M. Mellado.
Abstract
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CONCLUSION. Long-standing Morel-Lavallée lesions of the trochanteric region and proximal thigh may present various MRI patterns that reflect their variable composition and stage of development. MRI may prove especially useful for characterizing these lesions when the trauma is remote and progressive growth or pain is present.
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Morel-Lavallée lesions are well known to orthopedic surgeons but are rarely mentioned in the medical literature. Also, Morel-Lavallée lesions have been listed under different names, including posttraumatic soft-tissue cyst [7], pseudocyst [2], Morel-Lavallée extravasation [2], or Morel-Lavallée effusion [3]. Related posttraumatic entities such as ancient hematoma [8] and chronic expanding hematoma [9] have been described and may indeed be found as the end stage of some long-standing Morel-Lavallée lesions.
In the acute traumatic setting, Morel-Lavallée lesions require surgical intervention to prevent infection [5]. However, Morel-Lavallée lesions may be initially missed or take some time to develop, which can make clinical diagnosis difficult [4, 5]. The lesions may also enlarge and become chronic or painful, which may lead to a misdiagnosis of soft-tissue tumor and may often require surgical excision with complete resection [1–5].
The purpose of this study was to review and describe the MRI of long-standing Morel-Lavallée lesions in five patients with trauma history. We emphasize the potential role of MRI for characterizing these lesions.
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Various parameters were systematically investigated in the clinical charts, including type of trauma, existence of contralateral lesion, occurrence of associated traumatic injuries, delay in clinical detection, history of anticoagulation or bleeding diathesis, pain, progressive enlargement, and consistency. The analysis of excisional specimens and the results of cultured fragments or aspirates were also reviewed if available.
The five patients were assessed with MRI using a 1.0-T unit (Symphony, Siemens) and a phased array body coil. The MRI protocol included axial and coronal spin-echo T1-weighted sequences (TR range/TE range, 510–580/15–20), axial fast spin-echo T2-weighted sequences (3,200–3,600/98–120), axial or coronal STIR sequences (TR/TE, 4,100/29; inversion time, 130 msec), and axial gradient-echo T2*-weighted sequences (977/29; flip angle, 30°). Complementary axial or coronal spin-echo T1-weighted sequences, with or without fat saturation, were obtained in three patients after a bolus IV injection of 0.1 mmol/kg of gadolinium dimeglumine (Magnevist, Berlex Canada).
The MR images were reviewed by a radiologist experienced in musculoskeletal MRI. Various MRI features were evaluated, including location, shape, margins, widest diameter, expansive effect, homogeneity, signal-intensity characteristics, and contrast enhancement. The existence of a capsule was recorded and characterized as complete, incomplete, or absent. A complete capsule was defined as a distinct peripheral ring visible in at least two imaging planes and conspicuous on most MR images. The existence of internal septa or fluid–fluid levels was also evaluated.
According to the standards of our institution, review board approval and informed consent were deemed unnecessary because of the retrospective nature of the study.
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Imaging Findings
The delay between the traumatic episode and the MRI study varied between 3
months and 34 years. Three lesions were located on the proximal thigh (Figs.
1A,
1B,
1C,
1D,
2,
3), and the other two were
found on the trochanteric region and proximal thigh (Figs.
4A,
4B,
4C,
4D and
5A,
5B,
5C). All the lesions were oval
or fusiform, had well-defined margins, showed a mean widest diameter of 12.6
cm (range, 10–29 cm), and appeared to be contained in the deep
subcutaneous and perifascial space adjacent to the fascia lata. All lesions
showed some expansive effect, generating a palpable bulge or compressive
deformity on adjacent muscles.
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When compared with skeletal muscle, three lesions were hyperintense, one lesion was isohyperintense, and one lesion was hypointense on the T1-weighted sequences. Three lesions were homogeneous, and the other two were heterogeneous. All lesions with T1 shortening were hypointense to subcutaneous fat on the T1-weighted sequences. When compared with skeletal muscle, all lesions were hyperintense on the initial T2-weighted sequences, two were homogeneous, and the other three were heterogeneous. All lesions with T2 lengthening were at least partially hyperintense to subcutaneous fat. STIR sequences were available for two patients and showed lesions with the same characteristics seen in the T2-weighted sequences. Gradient-echo recalled T2-weighted sequences were available for one patient and showed the lesion to be the same as in the corresponding T2-weighted sequence. Fat-saturated T1-weighted sequences were available for one patient, and the lesion did not show signal loss.
A thin hypointense ring, most likely representing a fibrous or hemosiderin-laden capsule, circumscribed all lesions. The capsule was found to be complete in three patients and incomplete or uneven in the other two. Partial internal septa were found in two patients. No fluid–fluid levels were present. Patchy internal contrast enhancement and mild peripheral contrast enhancement were noted in one of the initial MRI studies and, in a different patient, in one of the follow-up MRI studies.
In one patient, follow-up MRI was performed 33 months after the initial study (Figs. 4C and 4D). The lesion in this study appeared isohyperintense on T1-weighted sequences and heterogeneously hyperintense on T2-weighted sequences when compared with skeletal muscle. In a different patient, a postsurgical follow-up MRI study was performed 55 months after the initial study and revealed residual effusion with similar signal-intensity characteristics.
Resulting Diagnosis
In one postoperative patient, the excised specimen was consistent with a
chronic organizing hematoma (Fig.
1D). In two other patients, the lesions were also interpreted as
chronic organizing hematomas on the basis of MRI findings (Figs.
2 and
3). In another patient, the
lesion was initially thought to represent a subacute hematoma (Figs.
4A and
4B) that probably became a
chronic organizing hematoma during follow-up (Figs.
4C and
4D). In the last patient,
successive percutaneous drainage procedures showed recurring sterile
serohematic effusions or seromas (Fig.
5A,
5B,
5C) that were débrided
surgically.
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Morel-Lavallée lesions may also show homogeneous hyperintensity on both T1- and T2-weighted MRI sequences and appear surrounded by a hypointense peripheral ring (Figs. 4A and 4B). This T1 signal-intensity behavior is probably related to the existence of methemoglobin, characteristic of subacute hematomas [10, 11]. Methemoglobin is first observed on the periphery of subacute hematomas and produces a "concentric ring" sign. As the hematoma evolves, it becomes progressively encapsulated and homogeneously hyperintense on T1-weighted sequences.
Long-standing Morel-Lavallée lesions may also show a third MRI pattern that includes variable signal intensity on T1-weighted images, heterogeneous hyperintensity on T2-weighted sequences, and a hypointense peripheral ring (Figs. 1A, 1B, 2, 3, 4C). Patchy internal enhancement and peripheral enhancement may also be present (Figs. 1C and 4D). The heterogeneous hyperintensity on T2-weighted sequences correlates with the existence of hemosiderin deposition, granulation tissue, necrotic debris, fibrin, and blood clots characteristic of chronic organizing hematoma [10, 11] (Fig. 1D). The hypointense peripheral ring has been found to represent a hemosiderin-laden fibrous capsule with mild inflammatory infiltrate, which is said to be relevant for the self-perpetuation of the lesion [8]. Finally, the internal enhancement is probably related to the capillary formation in the lesion (Fig. 1D).
The differential diagnosis of Morel-Lavallée lesions includes other subcutaneous lesions of posttraumatic origin, like fat necrosis [12] or coagulopathy-related hematoma. The potential of long-standing Morel-Lavallée lesions to clinically and radiographically resemble soft-tissue tumors had been previously acknowledged [7], particularly when pain and progressive enlargement are present. The history of trauma, the characteristic location, and the MRI features may contribute to a correct diagnosis in such cases.
Our study has some limitations. It is retrospective and is based on relatively few cases. Surgical correlation was available only in two patients, and aspirated fluids were analyzed in only two others. MRI follow-up studies were available for only two patients. However, the common clinical setting and the MRI features of the lesions were thought to assure a correct diagnosis in all cases.
In conclusion, MRI may help to characterize long-standing Morel-Lavallée lesions of the trochanteric region and proximal thigh, particularly when progressive growth or pain clinically mimic soft-tissue tumor. In a patient with a history of trauma to these regions, the presence of a moderately expansive subcutaneous oval or fusiform encapsulated lesion located in the perifascial plane adjacent to the fascia lata may reflect a long-standing Morel-Lavallée lesion. Waterlike content should suggest a seroma. Homogeneous hyperintensity to skeletal muscle and subcutaneous fat on T1-weighted sequences should suggest a subacute hematoma. Finally, heterogeneous T2 hyperintensity and patchy internal enhancement are consistent with a chronic organizing hematoma.
Acknowledgments
We thank John Bates and the language service of the Rovira i Virgili
University for their assistance in preparing the manuscript.
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