Intense FDG Uptake in the Common Bile Duct Post-ERCP Mimics Acute Infectious Cholangitis

Round 1

Reviewer 1 Report

 Dear author,

A glimpse of the image of the FDG-PET of the CBD is very interesting as in my knowledge there is scarce reports highlighting the false positive FDG-avid CBD attributable to physiological or non-carcinomatous aetiologies. Nevertheless, the case ase of intense FDG uptake in the CBD thought to be due to resolving  inflammation in a patient likely caused by ERCP may be skeptical to be ascertained as the only imaging that rule out the causes was the MRI which was only performed 9 days post FDG PET. Furthermore, the evolution of inflammation remains un-answered as the ERCP procedure was performed 1 month prior.

In this regards, I doubted that the portray of the likelihood of FDG-avid CBD could be caused by inflammation per-se, as other causes i.e biliary reflux, intestinal reflux and CBD peristaltic spasm could have be the potential cause to exhibit the FDG-avidity on the CBD.

There were also no delayed FDG-PET was done to exclude the physiological uptake of the spasm of smooth muscle of the CBD as tough the rest of the intestinal FDG-avidity shown on the coronal images.

I suggest, further elaboration and discussion about the likelihood cause of the FDG-avidity involving the CBD could further be discussed with supporting literature evidences would enhance the highlight of the case.

Author Response

Dear Reviewer,

Thank you for taking time to review the case report and for your comments.

1. We presented an incidental finding in a patient with suspected lung cancer referred for FDG PET. In our centre, FDG PET/CT is indicated only for oncological applications, not for infectious/inflammatory processes. Unfortunately, there is no imaging follow up with FDG PET for this patient, and therefore the etiology of intense uptake in the common bile duct remains speculative, mainly dependent on the available imaging findings and clinical information.
2. Biliary reflux is typically seen on HIDA scan with uptake in the stomach. It is unclear to us what intestinal reflux means. Could you explain? Does it mean that the content in the duodenum refluxes up to the CBD?
3. We have added a paragraph to clarify the reason for no FDG PET follow-up and mentioned the possibility of smooth muscle spasm of the CBD. Unfortunately, despite an extensive search, we were unable to find any studies evaluating FDG uptake in the CBD due to muscle spasm or intestinal reflux in the literature. If you are aware of any such studies, we would be happy to include them in our references.

Following paragraph has been added:

“In our centre, FDG PET is only performed for oncology indication. In this patient with a solitary lung lesion referred for FDG PET with incidental findings of CBD uptake post-ERCP, there was no indication for FDG PET follow-up. The etiology of the intense FDG uptake is speculative, based on the available radiological and FDG PET imaging, as well as clinical follow-up. The intense FDG uptake could possibly be due to CBD smooth muscle peristaltic spasm, although no such findings have been documented.”

We also changed the sentence, “The incidental findings of intense uptake in the CBD in our case are likely could be representative of a resolving inflammatory process due to ERCP or exaggerated by ERCP”

In addition, the following is added for other causes of CBD uptake documented in the literature:

“Increased uptake in the CBD associated with malignant and benign neoplasm has been reported. Cholangiocarcinoma and invasive intraductal papillary neoplasm of the bile duct are FDG avid^8–10. FDG uptake in the CBD has been reported in rare tumors such as malignant intraductal papillary mucinous neoplasm of the bile ducts¹¹,  tubular adenoma of the CBD¹², and biliary papillomatosis¹³. It has also been reported in CBD tuberculosis¹⁴ and bile duct thrombosis associated with hepatocellular carcinoma¹⁵”

Reviewer 2 Report

This is an interesting case. It's really rare that the intense FDG uptake in the common bile duct 1-month post-ERCP. So I have the following questions for you:

(1)To illustrate clearly the site of uptake, can you provide more PET/CT pictures, for example transverse, sagittal and MIP picture?

(2)From the CT and MRCP findings of different time, it seems that the inflammation was alleviated. Can you describe the changes with detail? 

(3) Are there any other diseases which can cause the similar PET findings (for example malignant, metastasis, et al.)? Can you add any disease and illustrate them?

(4) In line 61, "mestastasis" should be metastasis, please check other minor spell.

Author Response

Dear Reviewer,

Thank you very much for your reviewing the case report and for your comments.

1. As suggested, we have provided additional MIP, transverse, and sagittal images, which showed FDG uptake localized to the common bile duct. In addition, there is FDG avid bowel uptake secondary to metformin use
2. Yes, the inflammation was alleviated, in alignment with the patient’s clinical improvement. More detailed description was provided in the figure caption s of CT and MRCP.
3. There are other diseases described in the literature associated with FDG uptake in the CBD. We have added the following paragraphs:

“Increased uptake in the CBD associated with malignant and benign neoplasm has been reported. Cholangiocarcinoma and invasive intraductal papillary neoplasm of the bile duct are FDG avid^8–10. FDG uptake in the CBD has been reported in rare tumors such as malignant intraductal papillary mucinous neoplasm of the bile ducts¹¹,  tubular adenoma of the CBD¹², and biliary papillomatosis¹³. It has also been reported in CBD tuberculosis¹⁴ and bile duct thrombosis associated with hepatocellular carcinoma¹⁵.”

“Nagasaki et al¹⁹ reported high FDG uptake at the site of biliary stent in a patient with pancreatic cancer, suspected to be related to focal inflammation caused by insertion of the metallic stent.”

We also added a paragraph to explain the reason for no FDG PET follow-up:

“In our centre, FDG PET is only performed for oncology indication. In this patient with a solitary lung lesion referred for FDG PET with incidental findings of CBD uptake post-ERCP, there was no indication for FDG PET follow-up. The etiology of the intense FDG uptake is speculative, based on the available radiological and FDG PET imaging, as well as clinical follow-up. The intense FDG uptake could possibly be due to CBD smooth muscle peristaltic spasm, although no such findings have been documented”

And a change in a sentence:

“The incidental findings of intense uptake in the CBD in our case are likely could be representative of a resolving inflammatory process due to ERCP or exaggerated by ERCP, supported by the patient’s lack of symptoms and normal follow-up MRCP. This is different from typical acute cholangitis caused by introduction of enteric bacteria through a contaminated endoscope.”  

4. The misspelling has been corrected and multiple editorial changes have been made. Thank you!

Round 2

Reviewer 1 Report

Dear Autthor

I have satisfied with all concerned raised in the manuscript with acceptable clarification

Author Response

Thank you. We have asked a native English speaker to go through the manuscript.

Reviewer 2 Report

As mentioned last time, this is a very good education case. After the author's magior revison, its desige is appropriate, and has sufficient result support with adequately described methods. So now it good to publicate. 

Author Response

Thank you!

We have asked a native English speaker to go through the manuscript and make appropriate edits.