Retroperitoneal fibrosis (RPF) is a well described clinical entity that is being diagnosed with increasing frequency. RPF is characterized by replacement of the normal tissue of the retroperitoneum with fibrosis and/or chronic inflammation. However, aetiology, clinical presentation and radiological appearance in many cases are protean. Up to 15% of patients have additional fibrotic processes outside the retroperitoneum. In the abdomen, RPF may spread contiguously to involve multiple structures in both the retroperitoneum and the peritoneal cavity or multiple non-contiguous sites may be involved. We retrospectively reviewed 30 patients (19 male, 11 female; age range 28-79 years) with biopsy proven RPF. Although we found RPF most commonly as an isolated fibrotic plaque in the lower lumbar region (18 patients), 12 patients (40%) presented with RPF in atypical locations (4 peripancreatic, 1 periduodenal, 7 pelvic). The RPF was non-malignant in 24 patients (21 idiopathic, 2 perianeurysmal, 1 ergot-derivative treatment) and malignant in six cases. We present a pictorial review of the varied appearances of RPF, concentrating on atypical sites. The radiological differential diagnosis and its appearance with various imaging modalities are discussed. Current concepts with respect to management, prognosis and treatment are summarized.

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PurposeThere are perineal templates for interstitial implants such as MUPIT and Syed applicators. Their limitations are the intracavitary component deficit and the necessity to use computed tomography (CT) for treatment planning since both applicators are non-magnetic resonance imaging (MRI) compatibles. To overcome these problems, a new template named Template Benidorm (TB) has been recently developed. Titanium needles are usually reconstructed based on their own artifacts, mainly in T1-weighted sequence, using the void on the tip as the needle tip position. Nevertheless, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns. The purpose of this work is to improve the titanium needle reconstruction uncertainty for the TB case using a simple method based on the free needle lengths and typical MRI pellets markers.Material and methodsThe proposed procedure consists on the inclusion of three small A-vitamin pellets (hyperintense on MRI images) compressed by both applicator plates defining the central plane of the plate's arrangement. The needles used are typically 20 cm in length. For each needle, two points are selected defining the straight line. From such line and the plane equations, the intersection can be obtained, and using the free length (knowing the offset distance), the coordinates of the needle tip can be obtained. The method is applied in both T1W and T2W acquisition sequences. To evaluate the inter-observer variation of the method, three implants of T1W and another three of T2W have been reconstructed by two different medical physicists with experience on these reconstructions.Results and conclusionsThe differences observed in the positioning were significantly smaller than 1 mm in all cases. The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes. The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.

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