AJR 2003; 181:1065-1070
© American Roentgen Ray Society
Evaluation of Complications After Sternotomy Using Single- and Multidetector CT with Three-Dimensional Volume Rendering
Arthur E. Li1 and
Elliot K. Fishman1,2
1 Russell H. Morgan Department of Radiology and Radiological Sciences, Johns
Hopkins University School of Medicine and Johns Hopkins Hospital, Baltimore,
MD 21287.
2 Johns Hopkins Outpatient Center, 601 N. Caroline St., Baltimore, MD
21287.
Received January 24, 2003;
accepted after revision February 28, 2003.
Address correspondence to E. K. Fishman.
Introduction
Complication rates for median sternotomy range from 0.5% to 5%, and
mortality rates from these complications range from 7% to 80%
[1]. Complications may affect
the presternal (cellulitis, sinus tracts, abscess), sternal (osteomyelitis,
dehiscence), or retrosternal (mediastinitis, hematoma, abscess) compartments.
CT has an integral role as an aid in evaluating and characterizing
poststernotomy complications, particularly when performed after postoperative
day 14 [2]. In addition,
because of its improved spatial resolution and ability to interactively
display complex anatomy, multidetector CT (MDCT) with three-dimensional volume
rendering can be useful for surgical planning. We describe how median
sternotomy is performed, discuss CT protocols for evaluating patients after
median sternotomy, and describe normal and abnormal findings on CT.
Median Sternotomy: Advantages and Surgical Technique
Median sternotomy is the incision of choice for cardiac surgery and is also
useful for accessing anterior mediastinal lesions and for bilateral pulmonary
procedures. The advantages of this incision are its provision of speed in
opening and closing and excellent exposure. The operative approach begins with
a vertical skin incision made from below the suprasternal notch to a point
between the xiphoid process and umbilicus. Next, the sternum is divided with a
power saw. A sternal spreader is then inserted and opened, exposing the
anterior mediastinum. The sternum is closed with four to seven stainless steel
parasternal sutures, the ends of which are securely twisted and buried in the
sternal tissues.
CT Protocol for Imaging the Poststernotomy Chest
For routine CT scanning of the poststernotomy chest, we use 3- to 5-mm
slice thickness reconstructed every 2–5 mm. For more detailed
examinations, we use 1.25-mm slice thickness reconstructed every 1 mm. Other
parameters include 140 kV, 100 mAs, and 0.5 sec per rotation on a 4-slice MDCT
scanner (Volume Zoom, Siemens Medical Solutions, Malvern, PA).
Three-dimensional (3D) volume renderings can be generated with 3D Virtuoso
volume-rendering software (Siemens Medical Solutions), used on a freestanding
Onyx Infinite Reality workstation (Silicon Graphics, Mountain View, CA) or a
O-2 workstation (Silicon Graphics) running 3D Virtuoso software.
Normal Postoperative Appearance
Normal postoperative changes can persist for 2–3 weeks and include
minimal soft-tissue infiltration with edema and blood in the presternal and
retrosternal compartments, focal air (Fig.
1A,
1B), and localized sharply
marginated fluid or hematoma. Focal dots of mediastinal air usually resolve by
postoperative day 7 but can persist longer. Normal postoperative changes do
not completely obliterate mediastinal fat planes, preserving some or most of
the mediastinal fat radiolucency. Most patients have defects in the sternum,
including gaps up to 4 mm wide, step-offs (sternal tables at different
levels), and impaction (overriding of the sternal halves). Even 6 months after
undergoing sternotomy, only half of the patients show complete healing of the
sternum, although union should be complete 1 year after the procedure
[3] (Fig.
2A,
2B,
2C).
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Fig. 1A. —64-year-old man, 5 days after coronary artery bypass
grafting, with normal postoperative findings. Axial contrast-enhanced CT scan
shows mediastinal fluid and foci of air, which can be considered normal
findings for first 2 weeks after sternotomy.
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Fig. 1B. —64-year-old man, 5 days after coronary artery bypass
grafting, with normal postoperative findings. Three-dimensional
volume-rendered CT scan shows small gap in sternum, which is common. Gap is
usually of no significance unless it is associated with clinical
instability.
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Fig. 2A. —Three patients at various stages of normal healing after
median sternotomy. Three-dimensional volume-rendered CT scan of 52-year-old
man obtained 16 days after coronary artery bypass grafting shows nonunion of
manubrium and partial nonunion of sternal body—normal findings at this
stage.
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Fig. 2B. —Three patients at various stages of normal healing after
median sternotomy. Three-dimensional volume-rendered CT scan of 64-year-old
woman obtained 14 weeks after heart transplantation shows complete healing of
sternal body, with continued nonunion of manubrium.
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Fig. 2C. —Three patients at various stages of normal healing after
median sternotomy. Three-dimensional volume-rendered CT scan of 71-year-old
man obtained 1 year after coronary artery bypass grafting shows complete
healing of both sternal body and manubrium.
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Poststernotomy Complications
The clinical diagnosis of poststernotomy infection is based on local signs
(excessive pain and tenderness, erythema, and sternal discharge) and systemic
manifestations (fever, sepsis, elevated WBC). However, many of these
manifestations are nonspecific findings in postoperative patients. Also, the
depth of infection is difficult to determine clinically; for instance,
purulent wound drainage can originate from a superficial infection in the
presternal compartment or from the deep mediastinal tissues with
mediastinitis.We discuss poststernotomy complications classified by
compartment as presternal, sternal, and retrosternal.
Soft tissues in the presternal compartment include the skin, subcutaneous
tissues, and muscles. In patients with no postoperative complications,
presternal soft tissues are usually normal. Infection in the presternal
compartment manifests as stranding, sinus tracts, or frank abscess (Fig.
3A,
3B). CT sinography can depict
the depth of sinus tracts and reveal any mediastinal communication. Sinus
tracts that reach the outer plate of the sternum are suggestive of
osteomyelitis. Presternal infections should be treated conservatively.
Hematomas in the presternal compartment can also be readily detected on CT
(Fig. 4A,
4B).
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Fig. 3A. —76-year-old man 2 months after sternal débridement for
mediastinitis that resulted from coronary artery bypass grafting. Axial
contrast-enhanced CT scan shows extensive inflammation with gas bubbles
compatible with abscess in subcutaneous tissues. Inflammation and fluid also
extend into mediastinal fat planes, compatible with concurrent
mediastinitis.
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Fig. 3B. —76-year-old man 2 months after sternal débridement for
mediastinitis that resulted from coronary artery bypass grafting. Axial
contrast-enhanced CT scan obtained at level inferior to A shows extent
of subcutaneous abscess and mediastinitis.
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Fig. 4A. —63-year-old woman with significantly decreased hematocrit
level 5 days after reconstruction for dehiscence that resulted from coronary
artery bypass grafting. Axial contrast-enhanced CT scan shows active
extravasation (arrow) from right ventricle through median
sternotomy.
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Fig. 4B. —63-year-old woman with significantly decreased hematocrit
level 5 days after reconstruction for dehiscence that resulted from coronary
artery bypass grafting. Axial contrast-enhanced scan shows active
extravasation of blood (arrow) into large hematoma in pectoralis
muscles. Tear in right ventricle measuring 7 mm was found and surgically
repaired.
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CT can help detect sternal complications such as dehiscence, paramedian
sternotomy, and osteomyelitis. A paramedian sternotomy, defined as an
off-center sternotomy incision, predisposes the patient to dehiscence because
the thin side of the sternum can be broken by the closing wires. If a
paramedian sternotomy is found in a patient with dehiscence, sternectomy and
closure with muscle flaps are indicated (Fig.
5A,
5B). Sternal instability (Fig.
6A,
6B,
6C) may present clinically as
a sternal click. Sternal dehiscence is closely associated with poststernotomy
infections, either as a precipitating event or as a result of an infection
caused by aberrant wound healing. CT findings of dehiscence include displaced
sternal wires and progressive widening of the incisional gap (Fig.
7A,
7B,
7C). Early sternal
osteomyelitis is difficult to differentiate from minor sternal irregularities
caused by the bone saw and anatomic variants. Eventually, frank bone
destruction, severe demineralization, and dehiscence are seen. CT can show
subtle erosions, periosteal reaction, sharply marginated sclerosis, and
swelling in the adjacent soft tissues (Fig.
8A,
8B). In equivocal cases, an
indium-111 WBC scan may be helpful
[4].
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Fig. 5A. —83-year-old man with fever and pain 7 days after pectoralis
flap repair of dehiscence that resulted from coronary artery bypass grafting.
Axial contrast-enhanced CT scan shows sternal débridement with partial
sternectomy and repair with pectoralis flap (arrow) interposed into
sternectomy site. Soft-tissue stranding in anterior mediastinum was compatible
with normal postoperative appearance, and patient responded well to
conservative treatment.
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Fig. 5B. —83-year-old man with fever and pain 7 days after pectoralis
flap repair of dehiscence that resulted from coronary artery bypass grafting.
Volume-rendered CT scan shows extent of sternal débridement.
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Fig. 6A. —Three patients with clinically significant sternal nonunion
after coronary artery bypass grafting associated with clinical sternal
instability that required subsequent surgical repair. Three-dimensional
volume-rendered CT scan of 73-year-old woman obtained 1 month after surgery
shows sternal nonunion.
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Fig. 6B. —Three patients with clinically significant sternal nonunion
after coronary artery bypass grafting associated with clinical sternal
instability that required subsequent surgical repair. Three-dimensional
volume-rendered CT scan of 65-year-old man obtained 2 months after surgery
shows sternal nonunion.
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Fig. 6C. —Three patients with clinically significant sternal nonunion
after coronary artery bypass grafting associated with clinical sternal
instability that required subsequent surgical repair. Three-dimensional
volume-rendered CT scan of 68-year-old man obtained 1 year after surgery shows
continuing sternal nonunion, although with some evidence of healing.
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Fig. 7C. —53-year-old man after coronary artery bypass grafting.
Volume-rendered CT scan shows that size of gap is within expectations of
immediate postoperative appearance, but progressive widening visible on axial
images is suspicious for dehiscence, for which patient underwent muscle flap
closure.
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Fig. 8A. —69-year-old woman who presented 2 months after coronary
artery bypass grafting with fever and sternoclavicular pain. Axial CT scan
shows erosion of left superior sternum and first rib (arrow) caused
by septic arthritis or osteomyelitis, with large inflammatory cavity in left
upper lobe.
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Fig. 8B. —69-year-old woman who presented 2 months after coronary
artery bypass grafting with fever and sternoclavicular pain. Volume-rendered
CT scan shows septic arthritis or osteomyelitis involving both
sternoclavicular joint (arrow) and junction of sternum and first left
rib.
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Prompt diagnosis and treatment of retrosternal complications, particularly
mediastinitis, are critical. Other retrosternal complications include
pericardial effusion, hematoma, loculated effusion, and empyema. Uninfected
mediastinal and pleural collections are common (Figs.
9A,
9B and
10A,
10B). Mediastinitis can be
challenging to diagnose. Obliteration of mediastinal fat planes and diffuse
soft-tissue infiltration with or without gas collections are suggestive of
mediastinitis. Frank abscesses are usually of low density and may contain gas
(Figs. 11A,
11B and
12A,
12B). Unfortunately, in the
early postoperative period, many of the findings suggestive of mediastinitis
overlap with normal postoperative edema and air and hence can be nonspecific.
One group of investigators found that up to postoperative day 14, CT findings
are nonspecific for mediastinitis; however, after day 14, CT findings are
highly indicative of mediastinitis
[2].
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Fig. 9A. —66-year-old man who presented with pain and fever 3 weeks
after thymoma resection. Axial CT scan shows 7-cm dense fluid collection in
anterior mediastinum that was later drained and found to be hematoma.
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Fig. 9B. —66-year-old man who presented with pain and fever 3 weeks
after thymoma resection. Axial CT scan obtained at level superior to A
shows acute deep venous thrombosis in left innominate vein
(arrow).
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Fig. 10A. —61-year-old man 7 days after coronary artery bypass grafting
with elevated WBC. Axial contrast-enhanced CT scan shows anterior mediastinal
fluid collection, which had decreased in density since previous examination
(not shown). Finding was compatible with evolving postoperative hematoma.
Fluid was found to be uninfected.
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Fig. 10B. —61-year-old man 7 days after coronary artery bypass grafting
with elevated WBC. Axial contrast-enhanced CT scan obtained at level inferior
to A shows moderate pericardial effusion, left pleural effusion, and
minimal mediastinal air.
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Fig. 11A. —72-year-old man 13 days after heart transplantation. Axial
unenhanced CT scan shows large anterior mediastinal fluid collection with
multiple foci of gas, compatible with abscess and mediastinitis.
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Fig. 12A. —76-year-old man who presented with high fever and purulent
wound drainage 14 days after coronary artery bypass grafting. Axial
contrast-enhanced CT scan shows anterior mediastinal fluid collection
containing foci of gas. It was later surgically drained and proven to be
abscess with mediastinitis.
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Fig. 12B. —76-year-old man who presented with high fever and purulent
wound drainage 14 days after coronary artery bypass grafting. Axial
contrast-enhanced CT scan obtained at level inferior to A shows extent
of mediastinal abscess.
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The Role of CT
CT can reveal the extent and depth of infection, which influence whether
treatment is surgical or medical, and if surgical, the type of surgery to be
performed [5]. Surgical
management is chosen for sternal complications and for mediastinitis. For
osteomyelitis, the depth of infection determines whether only outer
débridement will suffice or sternectomy is required. The extent of
mediastinitis, including determination of pleural or pericardial involvement,
may help in determining the extent of exploration and débridement
[6].
Three-dimensional volume-rendered scans of the poststernotomy chest offer
several advantages over two-dimensional axial views. Volume-rendered images
can be rotated in an infinite number of angles and cut along any axis or
plane, allowing improved determination of the depth of infection or the path
of sinus tracts. Volume-rendered images are well suited for depicting
paramedian incisions. In cases of osteomyelitis, volume-rendered images can
help determine the extent of infection and whether both inner and outer plates
are involved. Volume rendering can also eliminate streak artifacts resulting
from sternal wires and clips.
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Introduction
Median Sternotomy: Advantages...
