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Original Report |
1 Department of Radiology, National Naval Medical Center, 8901 Wisconsin Ave.,
Bethesda, MD 20889-5600.
2 Department of Radiology and Nuclear Medicine, Uniformed Services University of
the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814.
3 Department of Radiology, University of Washington, 1959 N.E. Pacific, Box
357115, Seattle, WA 98195-7115.
4 Gastroenterology Service, Walter Reed Army Medical Center, Bldg. 2, 7F, 6900
Georgia Ave., N.W., Washington, DC 20307.
Received November 12, 2001;
accepted after revision March 4, 2002.
The opinions and assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Departments of the Navy, Army, Air Force, or Defense.
Abstract
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CONCLUSION. CT showed lobulated soft tissue involving the entire abdominal wall PEG tract in all proven cases. CT is an effective method for evaluation because the tumor burden lies predominately in the abdominal wall and not at the entry or exit site. The stomal implant is often the only site of metastatic disease at presentation. In general, CT findings of mildly increased soft tissue along the PEG tract are nonspecific, but a lobulated mass is highly suspicious for tumor implantation, especially if the one-sided thickness exceeds 1 cm. The preponderance of evidence from the existing literature points to direct tumor implantation during endoscopic placement as the likely cause (rather than hematogenous spread). This conclusion would support the alternative of radiologic tube placement in these patients.
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CT review was focused primarily on the PEG site, which was evaluated for the presence of soft tissue around the gastrostomy tube. The degree of involvement at the cutaneous exit site, abdominal wall tract, and gastric entry site was subjectively assessed. Estimated dimensions of the abnormal soft tissue were recorded. CT evidence of additional sites of abdominal metastatic disease was evaluated.
The available clinical and pathologic data were reviewed for these four patients. Portions of their clinical information have been previously described in medical case reports or letters, but the CT findings have not been emphasized [4,5,6]. The CT findings were correlated with images from endoscopic examination in two patients and with photographs of the PEG exit site in three patients.
In addition, 25 CT scans from 20 cancer patients with PEG tubes in place but with no stomal metastatic disease were reviewed in a similar fashion to provide data on the specificity of CT findings. These studies were performed an average of 3.4 months after PEG tube placement (range, 2 days-13 months). No obvious concern existed for stomal infection or mass in any of these patients. None of these patients has subsequently developed PEG stomal metastasis on clinical follow-up.
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CT revealed lobulated soft tissue surrounding the PEG tubes in all four patients (Figs. 1A,1B,1C,1D,2A,2B,3). The maximum width of soft tissue perpendicular to the PEG tube (measured on one side only and excluding the tube itself) averaged 2.1 cm (range, 1.0-2.8 cm). The soft tissue extended along the entire PEG tract within the abdominal wall, which measured an average of 5.9 cm in length (range, 5.6-6.0 cm). The left rectus abdominis muscle was asymmetrically enlarged where it was traversed by the PEG tube in all four patients, and direct tumor extension into the muscle was apparent in two patients. The tumor made contact with the gastric entry site and the cutaneous exit site in all four patients. Gastric entry site involvement was more prominent than cutaneous exit site involvement in two patients (Fig. 1A,1B,1C,1D), whereas exit site involvement predominated over entry site involvement in the other two patients. No other evidence of intraabdominal metastatic disease was seen in any patient. The PEG lesion represented a solitary metastasis in two patients; the other two patients had limited extraabdominal metastatic disease.
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Three of the four CT examinations were performed at or shortly before the time of clinical diagnosis of the implantation metastasis but after symptoms had developed. CT of the fourth patient (Fig. 2A,2B) was performed at a subclinical stage 3 months before symptoms developed, at which time bleeding from the PEG stoma was presumed to be due to granulation tissue. CT of two patients performed before the index CT (but after PEG placement) showed that the soft tissue had clearly progressed in the interval. The CT findings of mildly increased soft tissue along the PEG tract on these earlier scans (Fig. 1B) were nonspecific and comparable to the appearance seen in some patients without implantation metastases.
The degree of involvement at the cutaneous exit site on CT correlated well with photographs of the abdomen that were available in three patients (Fig. 1A,1B,1C,1D). Likewise, the gastric entry finding seen on CT correlated well with photographs obtained from upper endoscopy in two patients (Fig. 1A,1B,1C,1D).
The 25 CT scans of the 20 patients with no PEG site metastases showed, at most, only minimal hazy soft-tissue infiltration adjacent to the PEG tube in the abdominal wall (Fig. 4). No patient showed a well-defined mass or lobulated contour to the soft tissue. The one-sided width of the ill-defined soft tissue adjacent to the tube measured less than 2-3 mm in most patients and never exceeded 4 mm. Mild or moderate fusiform thickening of the left rectus abdominis muscle was noted in 11 (55%) of 20 patients and appears to correspond to a normal or nonspecific finding.
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Malignancy of the upper aerodigestive tract is a common clinical indication for feeding gastrostomy [1]. Metastatic seeding of the gastrostomy stoma is an unusual complication that can be seen in this subset of patients. The overall incidence is unknown, but case reports have been increasing in frequency [1,2,3,4,5,6]. On the basis of our experience, the incidence may be as high as 3%. All 27 reported cases of stomal metastases after percutaneous gastrostomy have involved tubes placed endoscopically via the os [1,2,3,4,5,6]. To our knowledge, no case has been reported after percutaneous radiologic gastrostomy. This absence is notable given the rather extensive clinical experience with percutaneous radiologic gastrostomy. To wit, one academic radiology department that places 500-700 gastrostomy tubes each year under fluoroscopy has had no case of stomal metastasis over a period of more than 15 years (Picus D, personal communication).
Our study shows that CT is an effective method for evaluating implantation metastases at the PEG site because the bulk of the tumor usually lies in the abdominal wall. Early disease is often clinically silent because the tube itself usually continues to function normally, even after the surrounding soft tissue has developed into a bulky mass. Furthermore, the early CT findings of hazy or mildly increased soft tissue are nonspecific and cannot be reliably distinguished from irritated or even normal granulation tissue [7]. Fusiform thickening of the ipsilateral rectus abdominis relative to the contralateral side is also a nonspecific finding that may be seen in most healthy patients with no tumor. Lobulated or increasing soft tissue seen along the PEG tube tract, however, should be viewed with suspicion, especially if the onesided thickness exceeds 1 cm. Extension to the cutaneous exit site (or, less frequently, the gastric entry site) is generally what leads to clinical presentation but is often delayed until the tumor has grown quite large or becomes complicated by bleeding, infection, or irritation [2,3,4,5,6]. Even when such cutaneous manifestations are present, a malignant cause is often not suspected initially [2]. These cancer patients may undergo CT for restaging or other indications, which affords an opportunity to examine the PEG region for abnormal soft tissue. Depending on the timing, CT would presumably detect most unsuspected implantation metastases before clinical manifestations develop, as seen in one of the four patients we present (Fig. 2A,2B).
The two leading hypotheses as to the mechanism of tumor spread to the PEG site are direct stomal seeding from tube contamination during placement and hematogenous spread. Each of these theories will be discussed in more detail because this issue directly affects which route of gastrostomy placement is most appropriate.
Seeding of the PEG stoma via tube contamination from direct tumor contact during endoscopic placement is a logical theory. Both the "pull" and "push" techniques entail passage of the gastrostomy tube through the oropharynx and esophagus, which results in direct tumor contact by the tube [1]. Translocation of dislodged tumor cells could result from this direct contact with the primary tumor. Substantial anecdotal evidence supports this theory, including the fact noted previously that all reported cases after percutaneous gastrostomy have involved PEG tubes placed via the os. The absence of any reported cases involving either radiologically placed gastrostomy tubes or PEG tubes placed by the "introducer" method (neither of which entails oral tube passage) further supports direct implantation as the mechanism of tumor spreading.
Port site tumor recurrences after laparoscopic and thoracoscopic tumor manipulations are well-documented phenomena [10]. Wound recurrences from open surgical procedures, however, are exceedingly rare, which lends further credence to the idea that the port site recurrences are the result of direct implantation and not hematogenous spread [10]. Tumor implantation of the percutaneous tract is a rare complication of radiologic procedures, including fine-needle biopsies and more invasive studies such as biliary interventions [11, 12]. Hematogenous spread to a fine-needle biopsy tract would seem highly unlikely given the minimal trauma involved.
One study examined the issue of metastatic spread to PEG stomata using predictions from tumor kinetics [4]. Using tumor-doubling times based on currently available biologic data, the authors concluded that direct tumor implantation seemed more feasible than hematogenous spread. The use of tumor-doubling times was particularly effective for explaining the rapid development of some stomal metastases that presented as early as 3 months after tube placement.
One argument in support of a hematogenous route is that coexistent hematogenous metastases are present in as many as half of all reported cases [5, 6]. However, coexistent hematogenous metastases are not present in a significant number of remaining cases, which seems to favor direct implantation even more. Nonetheless, hematogenous spread may have accounted for at least some of the reported cases. One case report of a stomal metastasis in a surgically placed gastrostomy tube also supports hematogenous spread [13]. Furthermore, some evidence exists from animal models that healing wounds are at increased risk for metastatic involvement by circulating tumor cells [14].
Although mostly anecdotal, these existing data strongly favor direct implantation over hematogenous spread as a cause of metastasis. This conclusion would support the practice of radiologic tube placement in this patient population to avoid direct contact of the tube with the primary tumor. Because stomal metastases tend to occur in patients with aggressive tumors and often carry a dismal prognosis, the route of tube placement is inconsequential. However, the stomal metastasis represents a solitary metastasis in approximately half of all cases [5, 6]. It remains unproven but conceivable that patient outcome would be improved by preventing a solitary implantation metastasis from occurring.
The small number of patients in this series is a limitation of our study that precludes firm conclusions. However, it is unlikely that any single institution will accumulate significant experience with PEG site metastases, so we reviewed the existing data from the many individual case reports in the literature. Another limitation of our study is that in none of the CT studies did patients with no stomal metastases have a history of stomal irritation or infection, which would have more fairly tested the specificity of CT findings.
In conclusion, CT is effective for evaluating symptomatic implantation metastases that complicate PEG placement in patients with malignancy of the upper aerodigestive tract. Although the CT findings of early asymptomatic stomal metastases are nonspecific, the observation of increased soft tissue along the PEG tract may warrant further investigation or close follow-up. Because ample anecdotal evidence supports direct tumor implantation from endoscopic tube placement as the predominate cause, percutaneous radiologic gastrostomy would seem more appropriate in these patients to prevent this complication.
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