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Home / Education / Journal Watch - March 2022 (1)

Journal Watch - March 2022 (1)

Diagnostic performance of 18F‑fluorodeoxyglucose‑PET/MRI versus MRI alone in the diagnosis of pelvic recurrence of rectal cancer

Verena Plodeck, Ivan Platzek, Johannes Streitzig, Heiner Nebelung, Sophia Blum, Jens‑Peter Kühn, Ralf‑Thorsten Hoffmann, Michael Laniado, Enrico Michler, Sebastian Hoberück, Klaus Zöphel, Jörg Kotzerke, Johannes Fritzmann, Jürgen Weitz, Christoph G. Radosa

Abdominal Radiology (2021) 46:5086–5094 https://doi.org/10.1007/s00261-021-03224-3

 

Colorectal cancer is the third most common cancer worldwide, and is expected that number will increase by around 60% to more than 2.2 million new cases by 2030. Rectal cancer accounts for about 40% of all cases of colorectal cancer (1,2).

Local recurrences rates have decreased significantly after the introduction of total mesorectal excision and neoadjuvant radiotherapy (3). In case of local recurrence, complete surgical resection is the only curative treatment, but due to the challenging method and the potential extent up to pelvic exenteration, accurate preoperative diagnosis is essential (4).

The diagnosis can be difficult, due to pelvic scarring and inflammatory/reactive changes after radiotherapy or anastomotic leaks (5,6). Follow-up of rectal cancer is usually done with CT, which is most commonly used, MRI and PET/CT. These methods have different sensitivities and specificities, with noticeable higher sensitivity in MRI versus CT, but comparable specificity. PET/CT was described to have a relatively low (58%) PPV for FDG-avid presacral lesions, but improved diagnostic performance after adding MRI sequences. A recent study demonstrated good accuracy of PET/MRI (7). The use of PET has been recommended in equivocal cases and prior to extensive resection (8).

The aim of this retrospective study was to compare 18F-FDG-PET/MRI and MRI in the diagnosis of pelvic recurrence of rectal cancer.

They included eligible forty-one PET/MRIs of forty patients, which were reviewed by four groups, in a blinded fashion, with a total of three radiologists and one nuclear medicine physician. To avoid bias, a time gap of 3 months was kept between the readings. Each finding was scored 0-4, depending on probability of recurrence.

MRI criteria for malignancy were:

  • On T2: nodular or irregularly shaped soft tissue masses, inhomogeneous structure, signal intensities equivalent or higher compared to muscle and/or infiltration of adjacent organs.
  • On DWI: high signal on b800 images with corresponding low signal on ADC maps.
  • On CE MRI: inhomogeneous enhancement with suspicious morphology on T2.

PET/MRI criteria considered shape, location and intensity, by visual assessment, of 18F-FDG uptake. Therefore:

  • Increased uptake compared to liver background was suspicious.
  • Lower uptake than liver background in anatomical structures like ovaries or rectal stump, typical uptake in the urinary tract or along bowel loops was considered benign.
  • Photopenic areas with slight uptake of the margins were considered fluid collections.
  • Non focal uptake, less compared to background, was presumed to be due to inflammation, if this corresponded to MRI.

Lesions were considered malignant if they showed intense focal 18F-FDG uptake, as well as suspicious MR findings.

The results showed that PET/MRI leads to less equivocal findings and increases readers’ confidence in diagnosing or excluding local recurrence. Inter-reader agreement, sensitivity, specificity, PPV/NPV and accuracy are comparable for MRI and PET/MRI, with slightly higher values for PET/MRI. Also, PET/MRI showed higher AUC (0.97 versus 0.92), but not statistically significant.

The authors referred to other studies. Comparing MRI results, Molinelli et al. obtained a higher AUC value for T2+CE-T1+DWI (9), but these results can depend on the experience of the readers and types of histology, for example mucinous tumors, included in the reviewed study, that has been shown to cause false negative results on ADC. Regarding PET/MRI results, Plodeck et al. (7) obtained higher specificity and NPV, but comparable sensitivity, PPV and accuracy.

This can be explained by some limitations to this study, because PET/MRI is used almost exclusively as second-line investigation, so a high number of recurrences is found, leading to a selection bias.

In conclusion, this study demonstrates that PET/MRI increases readers’ confidence levels and reduces the number of equivocal findings compared to MRI alone. It can be clinically useful in patients with equivocal findings in other imaging modalities, particularly in a preoperative setting.

 

References:

 

  1. Bray F, Ferlay J, Soerjomataram I, et al (2018) Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin 68:394–424. https://doi.org/10.3322/caac.21492 2
  2. Arnold M, Sierra MS, Laversanne M, et al (2017) Global patterns and trends in colorectal cancer incidence and mortality. Gut 66:683–691. https://doi.org/10.1136/gutjnl-2015-310912
  3. van Gijn W, Marijnen CA, Nagtegaal ID, et al (2011) Preoperative radiotherapy combined with total mesorectal excision for resectable rectal cancer: 12-year follow-up of the multicentre, randomised controlled TME trial. Lancet Oncol 12:575–582. https://doi.org/10.1016/S1470-2045(11)70097-3
  4. Law WL, Chu KW, Choi HK (2000) Total pelvic exenteration for locally advanced rectal cancer. J Am Coll Surg 190:78–83. https://doi.org/10.1016/S1072-7515(99)00229-X 14
  5. Even-Sapir E, Parag Y, Lerman H, et al (2004) Detection of Recurrence in Patients with Rectal Cancer: PET/CT after Abdominoperineal or Anterior Resection. Radiology 232:815–822. https://doi.org/10.1148/radiol.2323031065 9
  6. de Lange EE, Fechner RE, Wanebo HJ (1989) Suspected recurrent rectosigmoid carcinoma after abdominoperineal resection: MR imaging and histopathologic fndings. Radiology 170:323–328. https://doi.org/10.1148/radiology.170.2.2911656
  7. Plodeck V, Rahbari NN, Weitz J, et al (2019) FDG-PET/MRI in patients with pelvic recurrence of rectal cancer: first clinical experiences. Eur Radiol 29:422–428. https://doi.org/10.1007/s00330-018-5589-6
  8. Georgiou PA, Tekkis PP, Brown G (2011) Pelvic colorectal recurrence: crucial role of radiologists in oncologic and surgical treatment options. Cancer Imaging 11:S103–S111. https://doi.org/10.1102/1470-7330.2011.9025
  9. Molinelli V, Angeretti MG, Duka E, et al (2018) Role of MRI and added value of diffusion-weighted and gadolinium-enhanced MRI for the diagnosis of local recurrence from rectal cancer. Abdom Radiol 43:2903–2912. https://doi.org/10.1007/s00261-018-1518-z

 

Dr. Alexandra Babici is a fifth and final year radiology resident at the County Clinical Emergency Hospital in Cluj-Napoca, Romania. Her main areas of focus include gastrointestinal imaging, as well as oncologic and hybrid imaging. She is also interested in non-vascular interventional radiology, such as image-guided biopsies. She is a fellow of the European Society of Radiology (ESR) and RSNA (Radiological Society of North America) and has participated in many congresses and conferences.