Guess-a-Case

Overview

Sex: male
Age: 44 years

History
No significant past medical history.

Laboratory data
Elevated C-reactive protein (432 mg/dl); leucocyte and platelet counts as well as hemoglobin level within normal limits.

Physical findings
Physical examination at admission revealed a healthy looking patient with an indurated edematous swelling of the right leg and small pretibial cutaneous vesicles. No fever was present.

Case text
The patient was admitted to our emergency room due to worsening pain of the right leg since two days. The patient had no trauma, but he reported on a eczema of the distal thigh since two weeks. Emergency MR imaging of the thighs was performed.

Imaging Details

Image 1-5
MR imaging of both thighs
(1,2) Coronal STIR images; (3) axial T1-weighted image; (4,5) axial T2-weighted fat suppressed images

Image 6-8
MR imaging of both thighs
(6,7) Contrast enhanced T1-weighted images with fat suppression

Questions and Answers

Show answers

Image 1-5

1. What are the imaging findings on the study?

Swelling of the right thigh with increased signal within the subcutaneous tissue and within the muscles is noted on STIR images . Axial T1- and T2-weighted MR images demonstrate thickening of the subcutaneous tissue and high signal within the deep muscle fascia with fluid collections. In addition, increased signal is seen within the muscles of the right thigh.

2. Does the administration of i.v. contrast characterize the nature of the lesion?

Yes, administration of i.v. contrast is mandatory in this case.

Image 6-8

3. Describe the imaging findings.

T1-weighted MR images following contrast administration show enhancement of the subcutaneous tissue as well as enhancement of the deep fascia of the hamstrings, gracilis and sartorius muscles. Enhancement of the adductor muscles is also seen. No abscess formation is noted

4. Can you imagine to what the fluid collections as seen on T2-weighted correlated during surgery?

These areas were verified as necrotic fascia during surgery.

5. What is the most likely diagnosis?

Necrotizing fasciitis.

Discussion

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Final diagnosis
Necrotizing fasciitis

Differential diagnosis
Cellulitis.

Discussion
Necrotizing fasciitis is rare but life threatening infection of the soft-tissue with a mortality of up to 70%. Necrotizing fasciitis typically involves subcutaneous and fascial planes of the extremities, the abdominal wall or the perineum. Necrotizing fasciitis is characterized by extensive necrosis of subcutaneous tissue and fascia usually accompanied by severe systemic toxicity. Group A streptococci are often identified as causative agent, but polymicrobial infection is common. Entry in the subcutaneous space can occur via disruption of the overlaying skin such lacerations, surgical wounds, insect bites or injections. Diabetes mellitus is widely considered as the most common predisposing factor. Several studies have shown that necrotizing fasciitis is markedly associated with diabetes. However, patients with otherwise compromised host defense, peripheral vascular disease and healthy individuals may also be affected.

Unless early surgical debridement is undertaken, widespread necrosis and septic shock will occur. The clinical diagnosis between cellulitis and necrotizing fasciitis can be extremely difficult. Hence, early detection and reliable preoperative assessment is essential for the patient's survival.

Several studies have shown that MR imaging is useful in the differentiation of necrotizing fasciitis and cellulitis. Imaging findings consistent with cellulitis include subcutaneous thickening with fluid collections on T2-weighted MR images. In addition, contrast enhancement of the subcutaneous tissue and/or superficial muscle fascia may be present. Contrary, for the diagnosis of necrotizing fasciitis additional involvement of deep muscle fascia with fluid collections, thickening, and enhancement after contrast administration should be present on MR images. However, since MR imaging tends to overestimate the extent of deep fascial involvement, the final diagnosis should be based on a combination of both clinical findings and MR imaging.

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Necrotizing fasciitis, Image 1	Necrotizing fasciitis, Image 2	Necrotizing fasciitis, Image 3

Necrotizing fasciitis, Image 4	Necrotizing fasciitis, Image 5	Necrotizing fasciitis, Image 6

Necrotizing fasciitis, Image 7	Necrotizing fasciitis, Image 8

Yes
		(85.0%)
No
		(10.4%)
Undecided
		(4.6%)