Methodology
We collected data on the utilisation of PET-CT in a regional CUP MDT during a one year period in 2017.
A retrospective review of all cases in which PET-CT was performed at the request of the MDT.
In particular,
we evaluated the questions being asked by the MDT and whether PET-CT was successful in answering them.
Results
A total of 204 patients were referred for discussion at the CUP MDT over the one year period.
20 PET-CTs were requested by the MDT and all were subsequently performed.
The questions proposed by the MDT for assessment by PET-CT are as follows:
- Where is the primary?
- Where is the best site for biopsy in terms of safest,
least traumatic and avoid sampling error?
- Functional imaging characterisation in complex cases
- Does imaging suggest a favourable prognostic subset of CUP?
- Is it localised disease?
- Work-up for Stereotactic Ablative Radiotherapy (SABR)
- Work-up for radiotherapy
We found that PET-CT was was successful in answering the clinical question from the MDT in 16 out of 20 cases and not useful in 4 cases.
In some cases,
the PET-CT was helpful in answering more than one question.
The following table summarises the PET-CT scan outcomes:
Outcome |
Number of cases |
Percentage of cases |
Primary Identified |
5 |
25% |
Guide for Biopsy |
8 |
40% |
Limited/Oligometastatic disease |
4 |
20% |
Favourable subset |
4 |
20% |
Tissue Characterisation |
5 |
25% |
Not useful |
4 |
20% |
We have grouped these outcomes into 4 categories and demonstrate cases of each:
Finding the primary
Case 1
A 71 year old female presented with unexplained weight loss.
She underwent a contrast-enhanced CT (CECT) chest,
abdomen and pelvis (Fig. 1) which demonstrated multiple lung nodules consistent with metastatic disease without an obvious primary.
A whole body PET-CT (Fig. 2 and below) demonstrated a focus of abnormal increased tracer uptake at the anal verge,
raising the suspicion of a primary anal cancer.
Fig. 2: Case 1 - 18F-FDG PET-CT shows abnormal increased tracer uptake at the anal verge
There was also some mild uptake in the larger sized pulmonary nodules (Fig. 3).
In retrospect,
there was some abnormal soft tissue density at the anal verge on the CT pelvis (Fig. 4),
corresponding to the abnormal area of PET-CT.
Following biopsy of the anal lesion,
this was subsequently proven to be metastatic anal squamous cell carcinoma.
Case 2
A 72 year old female presented with a lump in the right groin.
An ultrasound scan (Fig. 5) and subsequent biopsy of the suspicious lymph node showed metastatic squamous cell carcinoma.
CT thorax,
abdomen and pelvis did not reveal a primary,
however,
subsequent whole body PET-CT demonstrated a focus of abnormal tracer uptake in the right vulva (Fig. 6 and below).
Fig. 6: Case 2 - 18F-FDG PET-CT shows abnormal increased tracer uptake in posterior aspect of the right vulva
In addition there was increased tracer uptake in the groin lymph nodes (Fig. 7).
These findings corresponded to an abnormality on pelvic magnetic resonance imaging (MRI) (Fig. 8).
A diagnosis of metastatic squamous cell carcinoma of the vulva was diagnosed.
Guiding the biopsy site
Case 3
A 70 year old male had multiple low signal skeletal lesions on MRI (Fig. 9),
suspicious for bone metastases.
CT thorax,
abdomen and pelvis showed a small lung nodule and right hilar node.
Prostate specific antigen (PSA) levels were normal and a myeloma screen was negative.
A CT guided biopsy (Fig. 10) of the right iliac lesion was reported as an inadequate specimen.
PET-CT was later performed and revealed the biopsy was taken in the least metabolically active region of the metastasis (Fig. 11 and below).
Fig. 11: Case 3 - 18F-FDG PET-CT shows abnormal increased tracer uptake in the right iliac bone lesion, with the least active region in the centre of the lesion
Following PET-CT,
a targeted biopsy was subsequently taken from the most metabolically active area,
avoiding the necrotic region and obtaining an adequate sample.
Case 4
An 83 year old female presented with weight loss.
CT thorax,
abdomen and pelvis revealed a large paraoesophageal lymph node (Fig. 12) with likely internal necrosis. This was also seen on endoscopic ultrasound (EUS) (Fig. 13) but the area of probable necrosis is not very conspicuous on EUS.
A PET-CT was performed and highlighted the region with the most intense tracer uptake (Fig. 14 and below).
Fig. 14: Case 4 - 18F-FDG PET-CT reveals the site of most intense tracer uptake to be in peripheral aspect of the lesion on the left
PET-CT allowed identification of the most hypermetabolic site within the lymph node,
helping to prevent a negative biopsy.
Functional imaging-based tissue characterisation
Case 5
A 70 year old male with a past history or prostate cancer 17 years ago,
for which he underwent radical prostatectomy,
had a CT performed demonstrating a solitary enlarged pre-sacral lymph node (Fig. 15).
It was unclear if this was a MUO or recurrence of prostate cancer after an unusually long period of remission.
The lesion was also not in a suitable location for percutaneous biopsy.
A PET-CT using the prostate-specific tracer Gallium 68-PSMA was performed which showed increased tracer uptake within the pre-sacral lymph node (Fig. 16 and below).
Fig. 16: Case 5 - 68Ga-PSMA PET-CT shows abnormal increased uptake in the pre-sacral lymph node
Gallium 68-PSMA PET-CT characterised the tissue as most likely being from a prostate origin,
without the need for invasive biopsy.
Case 6
A 75 year old male with a past history 3 years ago of follicular thyroid cancer with skeletal metastases,
confirmed on iodine-131 single photon emission computed tomography/CT (131-I SPECT-CT) (Fig. 17).
This was treated 3 times with 7.4GBq of radioiodine and subsequent imaging showed remission.
The patient developed a lung nodule and left adrenal lesion diagnosed on CT 3 years later.
It was not known if this was related to recurrence of the thyroid cancer or metastatic bronchogenic carcinoma.
The lung nodule did not show any increased tracer uptake on 131-I SPECT-CT (Fig. 18) and nor did the left adrenal lesion (Fig. 19).
18F-FDG PET was later performed for further characterisation and showed intense uptake at both sites (Fig. 20 and below).
Fig. 20: Case 6 - 18F-FDG PET shows abnormal increased tracer uptake in the right upper lobe pulmonary nodule and the left adrenal lesion
In this case,
PET-CT helped to characterise the findings as metastatic bronchogenic carcinoma rather than recurrent follicular thyroid cancer.
Identifying a favourable prognostic subset
Case 7
A 69 year old female presenting with abdominal pain underwent a CT abdomen which demonstrated a soft tissue density mass within the spleen (Fig. 21).
A completion staging CT was performed which did not highlight any other significant abnormality.
Biopsy was felt to be too high risk given the high vascularity of the spleen.
The nature of the mass remained uncertain and following discussion at the CUP MDT,
a PET-CT was obtained.
This revealed that the mass was intensely PET-avid,
with no other sites of uptake elsewhere in the body (Fig. 22 and below).
Fig. 22: Case 7 - 18F-FDG PET-CT showing intensely abnormal tracer uptake throughout the splenic mass. There were no other sites of abnormal tracer uptake on this whole-body study
The standardised uptake value (SUV) was measured at 27.
Given such intense uptake and the lack of disease elsewhere,
a diagnosis of lymphoma limited to the spleen was made.
In this case,
PET-CT aided in both classifying the patient into a favourable prognostic subset and providing functional information for tissue characterisation.