Description

A woman in her 20s with an unremarkable medical history was admitted to our institution for a 2-month history of abdominal pain and a hypoechoic retroperitoneal lesion found on ultrasonography (figure 1A). Physical examination (including cardiovascular, respiratory, neurological, skin and musculoskeletal system examinations) was unremarkable; blood count, together with eosinophil count, and serum biochemistry, including liver and renal function tests and serum IgG4, were normal.

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Figure 1

An ultrasonography (A) shows a hypoechoic mass. Enhanced CT scan (B) confirms the presence of a well-defined mass in the retroperitoneal space. On MRI, the mass appears as an ovoidal, hypointense lesion on T1-weighted images (C); in venous phase (D), the lesion has a ‘rim-like’ pattern of contrast enhancement, that can be observed also in Castleman disease.

No polyclonal hypergammaglobulinaemia was found on serum protein electrophoresis.

CT scan showed a retroperitoneal mass (figure 1B) with homogeneous contrast enhancement, proximal to the pancreatic body-tail, left adrenal gland and spleen, associated with localized lymphadenopathy. The thorax and the mediastinum were unremarkable.

On MRI, the 39-mm lesion was hypointense on T1-weighted (figure 1C,D) and hyperintense on T2-weighted images, with strong enhancement and rapid wash out of the centre, and progressive enhancement of the periphery in the equilibrium phase.

Since malignancy could not be excluded, the mass was surgically resected with the adherent structures.

Macroscopically, a whitish, firm mass measuring 3.5 cm in diameter was observed. Microscopically, the lesion consisted of dense fibrous tissue embedding an infiltrate of lymphocytes and plasma cells with germinal centres, admixed with eosinophils (figure 2A). The plasma cells were polytypic for kappa and lambda Ig-light chains. IgG4-positive plasma cells (figure 2B) were 20 per high-power field, with an IgG4/IgG-positive plasma cell ratio of 20%–25%. Castleman-like changes (ie, atretic germinal centres, increased vascularity and broad mantle zones) were present in the mass and the adjacent lymph nodes (figure 2C). A proliferation of CD23-positive follicular dendritic cells was seen (figure 2D). Immunostaining for HHV8 was negative.

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Figure 2

Microscopically, (A) the lesion consists of dense fibrous tissue in which an infiltrate of lymphocytes, plasma cells and eosinophils can be observed; the mass adheres to the adjacent pancreas (arrow), without infiltrating it (H&E 4.8×). Immunostaining for IgG4 (B) shows scattered positive plasma cells within the lesion (20×). Variably sized germinal centres, some of which atrophic with sclerosis are present in the mass and in the adjacent lymph nodes ((C), H&E, 4×). An expansion of CD21-positive follicular dendritic cells is seen ((D), 8.75×). Some of these findings can be observed in Castleman disease.

On the basis of the clinical and morphological findings, a diagnosis of idiopathic retroperitoneal fibrosis was rendered.

Retroperitoneal fibrosis (RPF) is a rare immune-mediated fibroinflammatory condition that can be secondary to infections, malignancies and drugs, or idiopathic (I-RPF), the latter accounting for approximately 75% of cases and being either IgG4-related or non-IgG4-related.1 IgG4-related-RPF belongs to the spectrum of IgG4-related disease (IgG4-RD), the diagnosis of which rests on the presence of characteristic clinical and histopathological (ie, dense lymphoplasmacytic infiltrate, storiform fibrosis and obliterative phlebitis) features, and an increased number of IgG4+ plasma cells (namely, IgG4+/IgG+ plasma cell ratio >40% and >10 IgG4+ plasma cells per HPF), as defined by the consensus statement on the pathology of IgG4-RD.2

In our case, the full criteria of an IgG4-RPF were absent, and this led to the diagnosis of a non-IgG4-related-RPF. However, the clinical utility of this distinction might be questionable, since the two forms seem to represent different ends of the same disease spectrum, the main difference lies in the higher frequency of extraretroperitoneal involvement in the IgG4-related-RPF.

As regard the presence of Castleman-like features, it is well recognised that inflammatory conditions such as I-RPF and multicentric and unicentric (more typically of the plasma cell subtype) Castleman disease (CD) can show overlapping clinical and pathological findings; on the other hand, CD can present with abundant IgG4-positive plasma cells and elevated serum IgG4 levels.3 Therefore, the differential diagnosis can be challenging.

For our case, the morphological criteria of CD were lacking, therefore an unequivocal diagnosis of CD could not be rendered. Besides, additional data such as C reactive protein (CRP), interleukin-6 and platelet count can be useful in this setting.4 In our case, these markers were normal.

Postoperative CT scan showed a clear surgical focus, and the patient was discharged symptom-free. She is currently in good condition and on tight clinical–radiological follow-up, with no evidence of recurrence or extraretroperitoneal manifestations on imaging and clinical examinations 1 year after surgery. In addition, medical therapy will be considered to prevent organ damage (eg, renal impairment due to ureteral obstruction). Currently, corticosteroids represent the first-line treatment for I-RPF.1 In refractory cases or when contraindications to glucocorticoid therapy are present, the use of rituximab represents a valid strategy, as it has been shown to be associated with a statistically significant shrinkage of RPF on post-treatment imaging, with a favourable side effect profile.5 Future studies are needed to further investigate the different therapeutic options in the systemic treatment of I-RPF.