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Original Research |
1 Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline
Ave., Boston, MA 02115.
2 Department of Surgery, Beth Israel Deaconess Medical Center, Boston, MA
02115.
Received November 4, 2004;
accepted after revision February 7, 2005.
Address correspondence to B. Siewert
(bsiewert{at}caregroup.harvard.edu)
(B. Siewert and G. Tye are co-first authors).
Abstract
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MATERIALS AND METHODS. We performed a word search of our CT database between July 2001 and July 2002 for the CT diagnosis of diverticulitis. CTs were retrospectively reviewed as consensus opinion of two reviewers. CTs were evaluated for presence of an abscess, its location, maximum diameter, and feasibility of percutaneous abscess drainage. Abscesses were categorized into smaller than 3 cm and larger than or equal to 3 cm, and the management of these groups was compared.
RESULTS. Thirty-one abscesses were noted in 30 (17%) of 181 patients with a CT diagnosis of diverticulitis. Twenty-two (73%) of 30 patients had 23 abscesses, all of which were smaller than 3 cm and were treated and resolved with antibiotics alone (p < 0.001). Eight (36%) of 22 required surgical treatment. Eight (26%) of 31 abscesses had a maximum diameter larger than or equal to 3 cm. Four (50%) of eight patients with abscesses 3.4-4.1 cm were treated with antibiotics alone. Four (50%) of eight abscesses, all larger than 4.1 cm, were treated with CT-guided drainage and one abscess required repeat drainage. After resolution of symptoms, surgery was performed in five (62.5%) of eight of the larger abscesses.
CONCLUSION. Patients with abscesses smaller than 3 cm in size can be treated with antibiotics alone and, in some cases, as outpatients, and may not uniformly require surgery. This is also likely true for patients with abscesses 3-4 cm in size, although our results in this group were limited by a small sample size. Patients with abscesses larger than or equal to 4 cm can be managed with CT-guided abscess drainage followed by referral for surgical treatment.
Keywords: abdomen • colon • CT • gastrointestinal radiology
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However, not all abscesses require an interventional drainage for resolution. Abscesses smaller than 3 cm in size are often treated conservatively with antibiotic therapy alone [12]. Furthermore, no clear guidelines exist for the optimal management of abscesses 3-5 cm in size. In addition, although elective resection has traditionally been offered after an episode of diverticulitis complicated by abscess formation, it is unclear if all patients with abscesses should undergo subsequent surgical treatment.
This study investigated the management and subsequent outcome of patients with diverticular abscesses. The purpose of this study was to provide additional data and to suggest guidelines for the treatment of small diverticular abscesses.
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CT Protocol
CT examinations were performed with a HiSpeed Advantage unit (GE
Healthcare) 45-60 min after the oral administration of 900 mL of a 2.1% barium
sulfate suspension (Readi-Cat 2, E-Z-EM). One hundred fifty milliliters of 43%
iodinated contrast material (Conray, Mallinckrodt Medical) was injected IV at
a rate of 2 mL/sec. Twenty-two (12.2%) of 181 patients did not receive IV
contrast because of elevated creatinine or contrast allergy. Single
breath-hold scans were obtained through the entire abdomen and pelvis with a
7-mm collimation and a pitch of 1.5 after a 50-sec delay. Coronal reformations
were performed in 147 (81.2%) of 181 patients. Three (1.7%) of 181 patients
received rectal contrast for better delineation of wall thickening.
Data Analysis
CT scans were retrospectively reviewed and interpreted as consensus opinion
of two radiologists who were blinded to clinical, surgical, and pathologic
findings. CT scans were evaluated for the presence, location, and maximum
diameter of an abscess, and the feasibility of percutaneous drainage for each
abscess was noted. An abscess was diagnosed when a fluid collection with an
enhancing rim was noted with or without air inclusion. If the CT examination
was performed without IV contrast, only fluid collections with convex borders
and mass effect were interpreted as abscesses. Abscesses were considered
unfeasible for imaging-guided catheter drainage when the collection could not
be reached percutaneously without passing traversing vital structures such as
small- or large-bowel loops or large vessels. Abscesses were categorized into
those smaller than 3 cm and those larger than or equal to 3 cm in their
maximum diameter, and the management of these two groups was compared.
Treatment of these patients was classified as medical (antibiotics alone),
radiologic (antibiotics and CT-guided percutaneous drainage), or surgical
(antibiotics and surgery). Statistical analysis was performed using the
chi-square test. Electronic medical records were reviewed for data regarding
the patients' initial clinical presentation, including symptoms (abdominal
pain, nausea, vomiting, anorexia, change in bowel habits), signs (fever,
abdominal tenderness, peritoneal signs), and laboratory findings
(leukocytosis, left shift, bandemia), and length of hospital stay. A minimum
follow-up of 50 days after the first presentation of diverticulitis was
obtained to track recurrent episodes of diverticulitis requiring subsequent
hospitalization, imaging studies, and surgery. Pathologic findings were
analyzed when available.
The evolution of the abscesses was categorized as resolution, persistence, or worsening. Persistence or recurrence of symptoms and subsequent surgical intervention were noted. Overall outcome was analyzed with data obtained from clinical follow-up, surgical reports, or both and compared between the two groups.
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All patients received antibiotics, with 11 (37%) of 30 treated as outpatients. The median follow-up period was 393 days (range, 50-758 days), during which 13 (43.3%) of 30 patients underwent elective resection for diverticulitis, six (20%) of 30 patients experienced mild recurrent or persistent symptoms of diverticulitis, and the remaining 10 (33.3%) of 30 patients remained free of symptoms with full clinical resolution.
Patients with Abscesses Larger Than or Equal to 3 cm
Eight (26%) of 31 abscesses had a maximum diameter larger than or equal to
3 cm. Four abscesses (50%) in eight patients were drained within 24 hr via a
CT-guided percutaneous catheter (Table
2) (mean size, 5.9 cm; range, 4.9-6.7 cm) (Figs.
1A,
1B, and
1C). The remaining four (50%)
patients were treated with antibiotics alone because the abscesses were judged
not to be amenable to drainage at the time because of their location deep
within the pelvis (Table 2)
(Figs. 2A and
2B). Abscess size in this group
ranged from 3.4-4.1 cm. All four patients showed resolution of the abscess on
follow-up CT (two patients) or on clinical evaluation (two patients). Only one
patient underwent surgery and showed acute inflammation in the surgical
specimen.
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One of the four patients who underwent radiologic intervention required a repeat percutaneous drainage because of reaccumulation of the abscess 10 days after the initial catheter had been removed (Figs. 1A, 1B, and 1C). The initial catheter had been in place for 12 days. Six (75%) of eight patients were admitted to the hospital with an average hospital stay of 5.8 days (range, 4-8 days), whereas two (25%) of eight patients were treated as outpatients. Six (75%) of eight patients reported a history of diverticulitis. Six (75%) of eight patients reported recurrent or persistent symptoms after treatment. Five (62.5%) of eight patients underwent surgical resection for diverticulitis at a median of 67.5 days (range, 34-644 days) after the acute episode. All surgical interventions were single-stage resections with primary anastamoses. Four (80%) of five patients showed acute inflammation on pathologic examination of the specimen. The remaining patient only showed chronic inflammatory changes, indicating response to treatment. Surgery was recommended but refused by one of the three patients who did not undergo eventual surgery. One patient was not a surgical candidate. The final patient, despite documented episodes of recurrent diverticulitis, had not undergone surgical evaluation or intervention at 544 days' follow-up for reasons unspecified in the clinical record. Thus, in total, interval surgery was recommended for seven (87.5%) of eight patients with large diverticular abscesses.
Patients with Abscesses Smaller Than 3 cm
Twenty-two (73%) of 30 patients had abscesses smaller than 3 cm in greatest
diameter, one of whom had two small abscesses. All 22 patients were treated
with antibiotics alone. Thirteen of 22 patients were admitted to the hospital,
with an average hospital stay of 5.5 days (range, 2-16 days). The remaining
nine (41%) patients were treated as outpatients with oral antibiotics.
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All patients who eventually underwent surgery (eight [36%] of 22 patients) had suffered multiple episodes of diverticulitis by the time of surgery, with six (75%) of these eight patients reporting a history of diverticulitis before the index episode in the present series and two (25%) experiencing recurrent episodes after their index presentation in the present series. Nine (41%) of the 22 patients reported full resolution of symptoms after the index episode and five (23%) had mild persistent or recurrent symptoms that did not warrant surgical intervention. Short-term and long-term treatments for small and large abscesses are listed in Table 3. Results were statistically significant (p < 0.05).
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In our study, a diverticular abscess was noted in 17% of patients with CT evidence of diverticulitis (32 of 181 patients). This is consistent with the incidence reported in the literature, ranging from 8-34% [3, 15-23]. The mean abscess diameter was 2.3 cm, with only eight (26%) of 31 abscesses equal to or exceeding 3 cm in diameter. Other studies have reported a mean abscess size of 3.3 to 5.4 cm [3, 15, 16]. The smaller size of the abscesses detected in our study may represent earlier diagnosis in our study population as a whole or less severe disease. Most patients in our study presented to the emergency department, where a CT scan was ordered on the day of presentation. Thus, as a result of increased number of patients with suspected diverticulitis undergoing CT early in the course of their disease, the abscesses detected in our study may have been smaller in size than those previously found in other studies. This trend is similar to the one reported for the diagnosis of appendicitis, in which an increase in CT led to diagnosis of disease in earlier stages [24]. Therefore, as CT becomes increasingly important in the evaluation of suspected diverticulitis [25, 26], an increase in the detection of small abscesses can be expected.
In our study, all abscesses smaller than 3 cm were treated successfully with antibiotics alone and thus did not require percutaneous drainage. In this patient population no recurrent abscesses required secondary catheter drainage. All patients who underwent surgery showed complete resolution of the inflammation on surgical pathology. In addition, even the four large abscesses that were not amenable to CT-guided drainage improved on antibiotic therapy alone. These abscesses measured 3.4-4.1 cm in diameter. None of these patients had recurrent abscesses. Only one (25%) of these four patients underwent surgery and showed acute inflammation in the surgical specimen.
These findings concur with the current recommendations from the American Society of Colon and Rectal Surgeons, the American College of Gastroenterology, and the European Association for Endoscopic Surgery, which state that small pericolic abscesses can initially be treated conservatively, with CT-guided abscess drainage reserved for those that fail to resolve [13, 27, 28]. However, none of these guidelines defines an abscess size that does not require CT-guided abscess drainage.
Only one study to our knowledge has attempted to establish a guideline for abscesses that are likely to respond to antibiotic therapy alone. Ambrosetti et al. [3] showed that the location of the abscess was the most important predictor of response to conservative therapy, concluding that mesocolic abscesses were more likely than pelvic or intraabdominal abscesses to respond to antibiotics alone. However, that study did not assess the effect of abscess size on response to medical therapy and included only inpatients in the study population. The abscesses encountered in their series were larger than in our study, ranging from 2 to 15 cm, with a mean size of 5.5 cm. Detry et al. [15], who reported on treatment options in acute diverticulitis depending on staging, found resolution of abscesses with bowel rest and antibiotic therapy alone in some of their patients, yet they also did not investigate the impact of abscess size on treatment.
In our population, all abscesses larger than or equal to 3 cm in diameter underwent CT-guided drainage when anatomically feasible (four [50%] of eight patients). Seventy-five percent of patients presenting with a large abscess reported persistent or recurrent symptoms after treatment, suggesting that presentation with a large abscess was associated with a more severe course of diverticular disease. This was underscored by reaccumulation of the abscess in one patient, requiring repeat CT-guided drainage.
Surgical treatment is recommended for all patients with an episode of diverticulitis complicated by abscess formation after their initial episode has resolved [13, 27, 28]. Chautems et al. [29] recommended that patients with evidence of a diverticular abscess on CT scan should be offered an elective colectomy, as they are more likely to have a poor outcome as defined by episodes of recurrent or persistent diverticulitis. In our study, surgery was performed in 13 (43%) of 30 patients: in five (62.5%) of eight patients with an abscess larger than or equal to 3 cm and in eight (36%) of 22 patients with an abscess smaller than 3 cm. Antibiotic treatment with or without percutaneous drainage provided sufficient resolution of acute inflammation for a single-stage resection in all patients who underwent surgery. However, in four of five patients with large abscesses who underwent surgery, acute inflammation was seen on surgical pathology. The need for surgical resection after resolution of an abscess with CT-guided drainage is under debate, with some authors suggesting that patients who are successfully treated for an acute episode of complicated diverticulitis with CT-guided abscess drainage may not require surgical resection at a later time [13]. However, at our institution, all patients who were treated with CT-guided drainage underwent subsequent surgical resection.
It is noteworthy that only 36% of patients with abscesses smaller than 3 cm required eventual surgery. Forty-one percent reported full resolution of symptoms and 23% reported improvement with mild recurrent or persistent symptoms that did not warrant surgery. These findings suggest that the course of disease in this population is not uniformly as severe as in patients with large abscesses and that contrary to current guidelines, the presence of a small diverticular abscess does not uniformly indicate a need for eventual surgery.
It has been shown that patients with uncomplicated diverticulitis are being treated increasingly as outpatients, with 65% of colorectal surgeons in one study reporting that they treat more than half of cases on an outpatient basis [14]. In our study, which included only patients with diverticular abscesses, nine (30%) of 30 patients with small abscesses were treated as outpatients and all showed clinical, radiologic, or pathologic evidence of resolution of their abscesses. Given that other patients with small diverticular abscesses were hospitalized for an average of 5.5 days, the ability to treat some patients on an outpatient basis would allow optimal treatment of disease with significant improvement in quality of life and decrease in overall costs. Several factors, including the patient's comorbidities, functional status, and support network, must also be taken into consideration in determining appropriate candidates for outpatient treatment.
In this study, we applied CT criteria for diagnosing abscesses as collections with an enhancing rim with or without air inclusion. However, since none of the small and four of the large collections did undergo catheter drainage, there is no proof that these collections were in fact abscesses as opposed to localized reactive peritoneal fluid collections, which has to be considered a limitation of this study. Similarly, resolution of diverticular abscess formation was not documented on imaging studies in seven of 22 patients who were followed clinically. The follow-up period was short in one patient (50 days). A larger number of patients will need to be investigated to more definitively address changes in current treatment recommendations. Another drawback of our study is using the somewhat arbitrary but institutionally accepted size cutoff of 3 cm as a guideline for intervening on a small abscess. Although this was chosen because of catheter constraints that make percutaneous drainage much more challenging in this population, further study is needed to determine more precisely the maximum size at which an abscess can be treated conservatively with antibiotics alone, reserving CT-guided drainage only for larger abscesses that are unlikely to resolve on their own. Another issue not addressed in this study is that of abscess aspiration [30], as at our institution, catheter drainage is preferred in the case of a diverticular abscess.
In conclusion, our findings suggest that the size of a diverticular abscess is of key importance in determining treatment and predicting outcome of patients with diverticulitis complicated by abscess formation. Patients with abscesses smaller than 3 cm can be treated with antibiotics alone and, in some cases, as outpatients and may not uniformly require surgery. This is also likely true for patients with abscesses 3-4 cm in size, although our results in this group are limited by small sample size. Patients with abscesses larger than or equal to 4 cm can be managed with CT-guided abscess drainage followed by referral for surgical treatment.
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3 cm)
