Imaging the bowel prior to VCE
Prior to the advent of the patency capsule in 2005, investigating small bowel patency was not routine practice for patients undergoing VCE. Thus, it not surprising that there are a number of asymptomatic patients with incidentally detected retained VCE capsules Fig. 8 .
Fig. 8: The importance of pre and post procedural imaging
A 77-year-old patient who was treated previously with radiotherapy for cervical cancer and developed radiation enteritis as a result. Investigated at an outside institution for abdominal pain but no pre or post procedural imaging was performed. The abdominal radiograph demonstrates three capsule endoscopes within the pelvis. The CT demonstrates these capsules lie in the small bowel (B), which is abnormally thick walled (C). One of the capsules had later perforated into the bladder.
Various imaging modalities are employed in evaluating small bowel patency:
- A) Small bowel follow-through
- B) CT enterography
- C) MR enterography and enteroclysis
A) Small bowel follow-through (SBFT)
√ SBFT can demonstrate strictures including approximate length and position
Fig. 9
× Doesn’t provide information about functional patency and can’t determine the ability of a VCE to safely pass, therefore underestimating the presence and significance of intraluminal stenosis resulting in VCE retention.
Fig. 9: Small bowel follow-through (SBFT):
66-year-old Crohn’s disease patient with a terminal ileal stricture. A SBFT cannot determine the functional patency of this stricture and thus a clinical decision for VCE cannot be made - INDETERMINATE FOR VCE
B) CT enterography (CTE)
√ CTE can demonstrate strictures including length and position Fig. 10
× Doesn’t provide information about functional patency.
Fig. 10: CT Enterography- 66-year-old with Crohn’s disease demonstrating mucosal thickening and increased enhancement at the terminal ileum with resultant intraluminal narrowing. Once again, functional patency and thus the safety of VCE cannot be determined - INDETERMINATE FOR VCE
Fig. 11: CT loop from patient in Figure 10. Mucosal thickening and hyperenhancement are demonstrated in the terminal ileum, but functional patency is not - Indeterminate for VCE.
C) MR enterography (MRE)
MR enterography revolutionised the investigation of small bowel involvement in Crohn’s disease. It has been demonstrated to have a high negative predictive value (>90%) in prediction of bowel stenoses likely to cause PC retention(10). However, it is not routinely used in assessing bowel patency prior to VCE.
Patency capsule: Proving patency
The aforementioned imaging techniques consist of high radiation doses, false negative results and do not adequately assess functional patency of the small bowel. The PC test enables the entirety of the small bowel to be interrogated and does provide information about functional patency.
The patency test (PT) is considered to be successful if any of the following are metFig. 12:
Fig. 12: Patency test criteria for proving functional small bowel patency
When the PT is negative, further investigations are warranted:
- The abdominal radiograph is limited as it cannot provide absolute evidence of the capsule within the large bowel Fig. 13.
- Fluoroscopy would require extensive screening and thus radiation doses in order to locate the capsule.
- The modality of choice is low dose CT abdomen/pelvis, which provides accurate information on the location of impaction.
Fig. 13: Pitfall of the abdominal radiograph. Abdominal radiograph of a 16-year-old with Crohn’s disease. The radiograph on the left demonstrates the patency capsule to be ‘within the ascending colon and thus safe for VCE’. Imaging after VCE however demonstrates capsule impaction of the VCE capsule by a terminal ileal stricture.
Fig. 14: Radiographs alone cannot ascertain whether it is safe to proceed with VCE, as the patency capsule could be within the terminal ileum or caecum, as demonstrated on the scout image. CT however demonstrates the patency capsule within caecum - SAFE FOR VCE
Fig. 15: 29-year-old with history of previous ileal surgery undergoing a patency capsule test. The scout image gives the impression that the patency capsule is within the sigmoid colon and thus safe to proceed to VCE. However, CT demonstrates clearly that the patency capsule has become impacted within a distal ileal loop proximal to the neo-terminal ileum - NOT SAFE FOR VCE
Fig. 16: 69-year-old patient with a retained patency capsule. Scout image finds the capsule to be within the hepatic flexure of the colon. CT confirms this as within the transverse colon - SAFE FOR VCE
Fig. 17: CT loop of the patient from Figure 16. Retained patency capsule is demonstrated in the transverse colon.
Retained PC may rarely cause small bowel obstruction Fig. 18. It is rare for invasive measures to be adopted to retrieve the capsules as spontaneous dissolution should occur and relive symptoms. However, there are cases of symptomatic retention requiring surgery (11).
Fig. 18: 85-year-old patient undergoing a PC test prior to VCE for suspected inflammatory bowel disease. Presented 24 hours following ingestion of PC with abdominal pain, distension and vomiting. The PC is visualised in the right iliac fossa with dilated, gas filled loops of centrally located small bowel, suspicious for small bowel obstruction.
Fig. 19: Axial CT loop of the patient from Figure 18. Retained patency capsule in the distal ileum causing upstream small bowel obstruction
Fig. 20: Coronal CT loop of the patient from Figure 18. Retained patency capsule in the distal ileum causing upstream small bowel obstruction.
Patency capsule- examination
In addition to imaging, careful inspection of the excreted PC can also help determine whether it is safe to proceed to VCE Fig. 21 . Medtronic discourage VCE if the body of the patency capsule be damaged.
Fig. 21: Patency capsule after egestion. Modified illustration from Medtronic’s brochure catalogue for PILLCAM SB (12).
A and B facilitate VCE.
C and D preclude VCE.
A) Intact PC and intact plugs
B) Intact body with eroded plugs
C) Eroded PC body
D) Empty shell and RFID tag
Original found at:
Metronic. The PillCam™ Patency Capsule is the best way to prove GI Patency prior to a CE Exam. In: Medtronic, editor. https://diagmedhealthcare/wp-content/uploads/2017/09/PillCam-Patency-Brochurepdf2016.
VCE retention
Capsule retention is an important risk which may lead to further complications. These include bowel obstruction, perforation and ischaemia. Some patients present with abdominal pain but others are asymptomatic. The risk of retention is higher in patients with established Crohn’s disease.
Fig. 22: 54-year-old patient with Crohn’s disease and previous small bowel surgery. The abdominal radiograph demonstrates the capsule endoscopy to be in the right iliac fossa, possibly within the small bowel. CT confirms retention within the neoterminal ileum.
Fig. 23: Coronal CT loop demonstrating the retained capsule within the neo-terminal ileum in the same patient from Figure 22
Fig. 24: 20-year-old patient with stricturing Crohn’s disease. Routine MR enterography was abandoned due to metal artefact visualised (A). An abdominal radiograph (B) found a radiodense structure in the mid-abdomen. This was demonstrated on CT enterography to represent retained video capsule endoscope (C), proximal to a small bowel stricture. The patient had forgotten that this procedure had occurred 3 years earlier.
Fig. 25: MR enterography loop of the patient in Figure 24. Metal artefact demonstrated in the mid abdomen. The examination was abandoned.
Fig. 26: CT enterography from the patient in Figure 24. Retained VCE visualised proximal to a small bowel stricture.
Atypical case
Fig. 27: 23-year-old patient undergoing a patency capsule test. CT scout image (A) finds the patency capsule to be within the left upper quadrant and thus a limited CT abdomen/pelvis was performed to minimise dose. A high-density ovoid structure is seen in the stomach (B), which was presumed to represent a retained patency capsule. However, the patency capsule is actually visualised in the descending colon, and the high-density structure in the stomach represents a pill (this is not seen on the scout image).