AJR 2004; 182:1195-1202
© American Roentgen Ray Society
Imaging Features of Soft-Tissue Infections and Other Complications in Drug Users After Direct Subcutaneous Injection ("Skin Popping")
Ciaran Johnston1 and
Mary T. Keogan
1 Both authors: Department of Diagnostic Imaging, St. James' Hospital and
Trinity College, James' St., Dublin 8, Ireland.
Received May 23, 2003;
accepted after revision September 12, 2003.
Address correspondence to C. Johnston.
Introduction
Drug abuse is a serious problem, both globally and at a local level, with
more than 13,400 opiate abusers in Dublin, Ireland, alone
[1]. Infectious complications
are responsible for 60–80% of hospital admissions of IV drug users
[2]. In 2000, in the United
Kingdom and Ireland, fatalities associated with soft-tissue inflammation and
severe systemic sepsis were linked to "skin popping" (injection of
drugs into the skin and subcutaneous tissues rather than directly into a
vein). Clostridium species were implicated in the pathogenesis
[3,
4]. Superficial infection may
progress to more widespread local or distant disease. Primary soft-tissue
infections in IV drug users include cellulitis, abscess, myositis,
pyomyositis, and necrotizing fasciitis. Secondary effects of IV drug use
include septic arthritis and tenosynovitis, secondary osteomyelitis, vascular
complications, soft-tissue ulceration, and fistula formation. In this review,
the range of complications caused by skin popping that may develop will be
shown. Early imaging to define disease extent and complications is important
because clinical deterioration can be precipitous.
Soft-Tissue Infections
Cellulitis
Acute infection of the skin and subcutaneous tissues may arise from direct
inoculation in drug injection. The diagnosis is usually clinical. Imaging
rules out abscess formation or other complication. Radiographic findings are
nonspecific and include soft-tissue swelling, displacement of fat planes, and
the presence of radiolucent gas foci if gas-forming organisms are present.
Radiopaque foreign bodies (e.g., needle tips) used by addicts may be discerned
(Fig. 1A,
1B). Sonography typically shows
skin and subcutaneous edema (Fig.
2A,
2B,
2C). This finding is not
specific for an infectious cause. CT and MRI show increased attenuation and
high T2 signal, respectively, in subcutaneous fat, which usually enhances
after administration of contrast medium (Fig.
3A,
3B,
3C).
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Fig. 1B. —22-year-old man with broken IV needle tip in left groin with
surrounding abscess formation. Contrast-enhanced CT scan of pelvis obtained
with soft-tissue window setting shows abscess formation (arrow)
around needle tip with diffuse enhancement and central low attenuation.
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Fig. 2A. —33-year-old HIV-positive woman with extensive anterior
abdominal wall cellulitis that extends into left leg. Focused sonogram of
anterior abdominal wall to left of umbilicus shows typical features of
cellulitis, including subcutaneous edema (solid arrows) interspersed
between echogenic fat lobules (open arrows). A = anterior, P =
posterior, M = medial.
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Fig. 2B. —33-year-old HIV-positive woman with extensive anterior
abdominal wall cellulitis that extends into left leg. CT scan filmed with
soft-tissue window setting again shows subcutaneous edema (arrows),
as evidenced by extensive areas of high attenuation within fat of anterior
abdominal wall but without deeper extension or abscess formation.
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Fig. 2C. —33-year-old HIV-positive woman with extensive anterior
abdominal wall cellulitis that extends into left leg. CT scan filmed with
soft-tissue window setting shows cellulitis extending into swollen left thigh
that shows marked edema, represented by areas of increased attenuation in
subcutaneous fat (arrowheads).
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Fig. 3A. —39-year-old man with superficial skin ulceration and
cellulitis of right leg caused by IV drug use. Coronal T1-weighted MR image
(TR/TE, 450/13) shows reticular low signal (arrows) in subcutaneous
tissues of right thigh and deep skin defect (arrowhead).
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Fig. 3B. —39-year-old man with superficial skin ulceration and
cellulitis of right leg caused by IV drug use. Unenhanced axial T1-weighted MR
image (500/20) with fat saturation shows cellulitis in subcutaneous tissues of
medial right thigh.
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Fig. 3C. —39-year-old man with superficial skin ulceration and
cellulitis of right leg caused by IV drug use. Contrast-enhanced axial
T1-weighted MR image (500/20) with fat saturation at same level as B
shows enhancement within area of cellulitis (arrows) but no
enhancement in adjacent adductor or quadriceps muscles.
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Abscess
In untreated addicts, cellulitis may evolve into a focal infected
collection, a subcutaneous or deep abscess. This may occur in unusual sites
(Figs. 4 and
5A,
5B).
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Fig. 4. —44-year-old woman with subcutaneous abscess in periumbilical
fat. Unenhanced CT scan of abdomen with soft-tissue window setting shows focal
homogeneous mass (arrow) of soft-tissue attenuation in left
periumbilical region, without surrounding cellulitis, suggestive of
abscess.
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Fig. 5A. —Incidental finding of right neck abscess in 28-year-old
HIV-positive man undergoing routine follow-up for cerebral toxoplasmosis.
T2-weighted image (TR/TE, 2,400/90) of head shows mixed-signal-intensity mass
involving right sternocleidomastoid muscle and overlying superficial tissues
(arrow). Incidental note is made of high-signal-intensity mass
(arrowhead) in left thalamus in keeping with known diagnosis of
cerebral toxoplasmosis.
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Fig. 5B. —Incidental finding of right neck abscess in 28-year-old
HIV-positive man undergoing routine follow-up for cerebral toxoplasmosis.
Subsequent sonogram of right anterior neck shows fluid collection with thick
walls (arrows) containing some low-level internal echoes with
through-transmission consistent with abscess. M = medial.
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On conventional radiography, even sizable abscesses may be difficult to
discern. Adjacent bones may show periosteal reaction and joints, sympathetic
effusions. Sonography shows a well-marginated fluid collection with
hyperechoic rim in the acute and subacute phases. Abscesses can appear more
complex, and echogenicity can vary associated with internal debris,
hemorrhage, or septum. Peripheral calcification must be differentiated from
gas. CT readily shows the extent of abscess formation. Abscess walls and any
internal septa typically enhance after contrast administration. Uncomplicated
fluid normally has low attenuation, but complicated fluid shows higher values
(Fig. 6A,
6B). Associated cellulitis is
easily perceived. MRI is more sensitive in depicting soft-tissue infections.
Fluid collections show intermediate to low signal on T1-weighted images and
high signal intensity on T2-weighted images, with peripheral enhancement after
contrast administration. Patchy intermediate signal in adjacent bones and soft
tissues is often reactive
[5].
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Fig. 6B. —30-year-old man with left groin abscess. CT scan filmed with
soft-tissue window setting after contrast material administration shows focal
fluid attenuation collection with subtle internal enhancement (small
arrow) and gas (arrowhead) in nondependent portions, suggestive
of abscess. Focal gas (large arrow) is also seen anterior to
collection. Aspiration confirmed presence of abscess.
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Pyomyositis
Pyomyositis, a pyogenic muscle infection that may progress to abscess
formation, is rare because skeletal muscle is relatively resistant to
infection. The introduction of an infected needle, often in subjects with
coexisting immunodeficiency, makes infection more likely. Radiographic
findings are nonspecific. Sonography has a limited role and shows increased
muscle volume or an intramuscular fluid collection. Cross-sectional imaging is
important. CT findings include thickening of skin and fascial planes,
asymmetry of muscle bulk, and areas of fluid attenuation in muscles whose
margins typically enhance after contrast administration if pyomyositis has
intervened (Fig. 7A,
7B). MRI may show areas of
pyomyositis not evident on CT
[6]. Involved muscles show
increased signal intensity on T1-weighted images and heterogeneously increased
signal intensity on T2-weighted images (Fig.
8A,
8B,
8C,
8D). Focal fluid collections
exhibit a uniformly high signal on T2-weighted images, often with a
low-intensity rim, which usually enhances after gadolinium administration.
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Fig. 7A. —22-year-old man with muscle affected by pyomyositis
progressing to abscess formation. CT scan obtained with soft-tissue window
setting shows gross enlargement of left thigh with extensive ulceration
(arrowheads) anteromedially and extensive cellulitis
(arrow). In addition, increased muscle bulk of hip extensor muscles
is present, but without fluid collection.
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Fig. 7B. —22-year-old man with muscle affected by pyomyositis
progressing to abscess formation. CT scan obtained 4 days after A shows
focal abscess with enhancing margins (arrow) in hamstring muscles of
left thigh and second abscess medially below ulcer (arrowheads).
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Fig. 8A. —34-year-old man with myositis of right deltoid and triceps
muscles caused by intramuscular injection of heroin and cocaine mixture.
Anteroposterior radiograph of right humerus shows mottled gas
(arrows) in soft tissues.
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Fig. 8B. —34-year-old man with myositis of right deltoid and triceps
muscles caused by intramuscular injection of heroin and cocaine mixture. CT
scan obtained with soft-tissue setting shows high-attenuation areas of
cellulitis (arrow) and low-attenuation areas of subcutaneous gas
(arrowheads).
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Fig. 8C. —34-year-old man with myositis of right deltoid and triceps
muscles caused by intramuscular injection of heroin and cocaine mixture.
Coronal T2-weighted MR image (TR/TE, 2,000/80) of left arm shows high signal
in triceps muscle (T) with extensive subcutaneous cellulitis. S = superior, I
= inferior, M = medial.
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Fig. 8D. —34-year-old man with myositis of right deltoid and triceps
muscles caused by intramuscular injection of heroin and cocaine mixture. Axial
T2-weighted MR image (2,000/80) of left arm shows diffuse increased signal in
left deltoid (D) and triceps muscles but no focal area of pyomyositis. M =
medial, A = anterior, P = posterior.
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Necrotizing Fasciitis
In this rare condition, subcutaneous and superficial necrosis is quickly
followed by involvement of fascial planes initially and then of the muscles
themselves, associated with severe systemic symptoms. Early diagnosis is
essential because surgical débridement is required. Findings at
conventional radiography and sonography mimic those of cellulitis.
CT and MRI are important to show fascial plane thickening, which typically
enhances after contrast administration. Subcutaneous and deep edema and any
coexistent abscesses may also be discerned. Viable tissue can be
differentiated from necrotic muscle by contrast material administration (Fig.
9A,
9B).
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Fig. 9A. —28-year-old man with bilateral buttock cellulitis and
pyomyositis of right gluteal muscles that progressed to necrotizing fasciitis
requiring surgical débridement. CT scan filmed with soft-tissue setting
shows enlarged right gluteus medius and maximus muscles with overlying skin
defect (solid arrow) and marked bilateral subcutaneous reticulation
caused by cellulitis (arrowheads). Some low attenuation is seen
within enlarged gluteus muscles (open arrow).
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Fig. 9B. —28-year-old man with bilateral buttock cellulitis and
pyomyositis of right gluteal muscles that progressed to necrotizing fasciitis
requiring surgical débridement. T2-weighted MR image (TR/TE, 2,500/80)
of upper thighs after débridement shows large surgical defect
(arrow) in posterior right thigh. In addition, extensive bright T2
signal (arrowheads) is seen in fascial planes of left thigh, typical
of fascial thickening seen in necrotizing fasciitis. This patient subsequently
died within 24 hr of overwhelming systemic sepsis.
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Other Local Complications
Vascular Complications
An addict may injure any vessel during injection, and the superficially
placed femoral artery is particularly susceptible to damage resulting in
hematoma formation, arterial dissection, thrombosis, and pseudoaneurysm
formation. Various imaging techniques may be used in characterizing such
lesions (Fig. 10). Venous
thrombosis is common and easily shown
(Fig. 11).
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Fig. 10. —Digital subtraction angiogram of right superficial and deep
femoral arteries in 38-year-old woman shows pseudoaneurysm (arrow)
arising from superficial femoral artery associated with repeated "groin
hits."
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Fig. 11. —19-year-old man who frequently injected heroin into
superficial neck veins because of poor venous access in his limbs. Coronal
T1-weighted MR image (TR/TE, 800/16) of neck shows lack of flow void in left
external jugular vein (arrow) caused by acute venous thrombosis after
episode of injection into vein.
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Secondary Osteomyelitis and Septic Arthritis
Spread of infection from superficial foci around needle tracks to adjacent
bones may occur [7]. The
soft-tissue component may be the major imaging feature. Radiography and CT may
show bone destruction or sequestrum formation in addition to other soft-tissue
signs [8]. MRI can show fluid
in marrow which, unlike reactive edema, may become more focal, analogous to
abscess formation after cellulitis (Fig.
12A,
12B,
12C). A connection between an
abscess and a focus of osteomyelitis through a cloaca may be seen. In bone
scintigraphy, both the infected bone and surrounding infected soft tissue show
increased radiotracer uptake in all three phases (Fig.
13A,
13B). Increased blood flow and
blood pool activity usually extend beyond the osseous margins.
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Fig. 12A. —35-year-old man admitted with severe left-sided lower back
pain radiating to left leg. He had numerous presentations previously with left
groin abscesses that required repeated surgical drainage. Coronal T2-weighted
MR image (TR/TE, 2,000/80) of lumbar spine shows diskitis at level of
L4–L5 disk with abnormal high signal from center of disk space (open
arrow) and adjacent vertebral bodies (solid arrows) caused by
extension from large adjacent abscess of psoas muscle.
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Fig. 12B. —35-year-old man admitted with severe left-sided lower back
pain radiating to left leg. He had numerous presentations previously with left
groin abscesses that required repeated surgical drainage. Sagittal T2-weighted
image (2,000/80) shows extension into L4–L5 disk, where abnormally high
signal in center of disk (open arrow) and in adjacent vertebral
bodies (solid arrows) exists.
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Fig. 12C. —35-year-old man admitted with severe left-sided lower back
pain radiating to left leg. He had numerous presentations previously with left
groin abscesses that required repeated surgical drainage. Contrast axial
T1-weighted image (750/20) at same level as B shows infected psoas
muscle pyomyositis (arrowheads) extending into adjacent tissue
planes.
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Fig. 13A. —23-year-old woman with recurrent right groin abscesses who
presented with pyrexia, back pain, and raised inflammatory markers. Delayed
posterior three-phase bone scintigram shows nonspecific finding of increased
radioisotope uptake (arrowhead) in right sacroiliac joint.
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Fig. 13B. —23-year-old woman with recurrent right groin abscesses who
presented with pyrexia, back pain, and raised inflammatory markers. CT scan
obtained with bone window setting shows bone destruction (arrow) at
right sacroiliac joint. Adjacent soft-tissue swelling was discerned with
soft-tissue settings. These findings were suspicious for osteomyelitis
affecting right sacroiliac joint, which was confirmed by subsequent joint
aspiration.
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Secondary septic arthritis and tenosynovitis may also occur. Imaging
reveals accumulation of fluid and pus within the joint or tendon and increased
vascularity.
Radiography may show soft-tissue swelling or joint effusion. Sonography and
CT may show fluid in the affected joint or tendon sheath. MRI is superior in
the depiction of fluid collections, with typical signal characteristics, and
tendonitis, evidenced by patchy increased signal on T2-weighted scans.
Miscellaneous
Soft-tissue ulceration at injection sites is usually evident clinically.
Imaging rules out deeper infection. In complicated abscesses, fistulas may
occur in adjacent bowel or joint. Sinography can delineate the extent of
abscess cavity or fistula (Fig.
14A,
14B).
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Fig. 14A. —54-year-old man, longtime injector of cocaine and heroin,
with bilateral groin complications. At initial presentation, venogram shows
meniscus sign (arrow) caused by acute right common femoral vein
thrombosis.
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Fig. 14B. —54-year-old man, longtime injector of cocaine and heroin,
with bilateral groin complications. Patient presented 6 months later with
discharging sinus from contralateral groin. Sinograph revealed tortuous
irregular sinus tract that communicated with adjacent thrombosed left common
femoral vein. Arrowheads show thin catheter in sinus tract opening with short
irregular connection to thrombosed vein.
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Conclusion
In drug addicts, skin and subcutaneous infection may result in extensive
local disease but may progress to serious and distant complications that can
be life threatening. Early diagnosis is imperative for commencement of
appropriate therapy.
References
- Comiskey C, Barry JM. A capture-recapture study of the prevalence
and implications of opiate use in Dublin. Eur J Public
Health 2001;11:198
–200[Abstract/Free Full Text]
- Trilla A, Miro JM. Identifying high risk patients for
Staphylococcus aureus infections: skin and soft tissue infections.
J Chemother1995; 7:37
–42
- Ebright JR, Pieper B. Skin and soft tissue infections in injection
drug users. Infect Dis Clin North Am2002; 16:697
–712[Medline]
- U.S. Centers for Disease Control and Prevention. Update:
Clostridium novyi and unexplained illnesses among injecting-drug
users—Scotland, Ireland, and England. MMWR Morb Mortal Wkly
Rep 2000;49:543
–545[Medline]
- Struk DW, Munk PL, Lee MJ, Ho SG, Worsley DF. Imaging of soft
tissue infections. Radiol Clin North Am2001; 39:277
–303[Medline]
- Applegate GR, Cohen AJ. Pyomyositis: early detection utilizing
multiple imaging modalities. Magn Reson Imaging1991; 9:187
–193[Medline]
- Monteagudo I, Rivera J, Lopez-Longo J, et al. AIDS and rheumatic
manifestations in patients addicted to drugs: an analysis of 106 cases.
J Rheumatol1991; 18:1039
–1042
- Tehranzadeh J. Musculoskeletal infection in the immunocompromised
patient. In: Taveras JM, Ferucci JT, eds. Radiology:
diagnosis-imaging-intervention. Philadelphia, PA:
Lippincott-Raven 1997:1
–20
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Introduction
Soft-Tissue Infections
