45-year-old female presenting with large retroperitoneal masses and previous history of breast fibroadenoma and cervical cancer (CIN 3) treated with surgery. The patient declared no pain at the time of imaging, although she had undergone 10 years earlier another surgical resection of a nodular mass in the left thigh.
Fig. 1. Contrast-enhanced CT, axial view showing large retroperitoneal masses (54mm, 43 mm and 60mm) in the paracaval, paraaortic and left common iliac region, resulting centrally hypodense and presenting some mild enhancement at the peripheral rim.
Fig 2. Coronal and sagittal localization CT (a, c) and fused 18F-FDG PET/CT (b, d) views document a similar behaviour of the lesions, with central photopenic areas and faint tracer accumulation (SUVmax 4.4) at the peripheral rim.
Fig 3. MIP (a) and coronal fused 18F-FDG PET/CT (b) document, in addition to the above-mentioned lesions, the presence of a small solid lesion in the left thigh showing a mild FDG uptake (SUVmax = 3.8).
Fig 4. Localisation CT (a, b) and fused 18F-FDG PET/CT axial views (c, d) document the round solid lesion (15mm) along the left femoral vein.
Fig 5. Contrast-enhanced CT, at the lower extremity of the field of view, documented a posteriori the solid lesion seen on 18F-FDG PET in the left thigh.
Schwannomatosis (SWN) is a rare genetic disorder embedded in the family of neurofibromatoses (NF), together with neurofibromatosis type 1 and 2 (NF1/NF2). Typical features characterizing these three NF forms comprise “café-au-lait” macules, cutaneous neurofibromas and Lisch-nodules for NF1, while schwannomas represent a distinctive sign for both SWN and NF2 .
Schwannomatosis disease is characterized by the development of multiple peripheral and central nerve sheath tumours, both benign and malignant, with the exclusion of the vestibular nerves, which are spared in SWN making this aspect part of the differential diagnosis with NF2 [2,3]. According to the clinical criteria mostly accepted, patients with 2 or more pathologically confirmed non-intradermal schwannomas, no evidence of vestibular nerve tumour on an imaging study performed after the age of 30 years and no known constitutional NF2 mutation could have a definite diagnosis of SWN [4, 5]. The lack of symptoms related to the eighth nerve dysfunction represents in fact a key element even in the case of SWN presumption . While other intracranial localizations tend to be very rare. Imaging plays an important role in the diagnosis of the disease and considers whole-body magnetic resonance imaging (WB-MRI) as the method of choice [1-6]. On the other hand, however, peripheral nerve sheath tumours tend to show increased metabolic activity on 18F-FDG PET/CT, allowing the contemporary detection of multiple schwannomas in various districts [7-12].
The case report herein illustrated represents a typical example of Schwannomatosis. After retrieving the clinical history of the patient, we discovered that the original mass removed from the left groin was a schwannoma, genetically negative per NF2, with a Ki67 of 5%. The long term survival of the patient, with most lesions being necrotic, is in line with the low FDG uptake documented on PET/CT. Although this modality is more widely used for imaging NF1, being a predictive marker of malignant transformation of the neurofibromas [1, 7], it might find a proper place in SWN as well. At first, it allows the exclusion of hypermetabolic foci, consistent with more aggressive tumours. Secondarily, being a whole-body imaging modality, it permits as in the present case to detect all tumour sites at once.
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