PMC9940164_01
X-ray of the left knee, face and profile, showing the presence of an opaque, oval, well-limited, subcutaneous soft tissue mass with clear contours, respecting the adjacent bony structures, opposite the upper end of the anterior tibial tuberosity.
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A radiograph of the knee was requested and showed an opaque oval shaped subcutaneous mass overlying the tibial tuberosity medially, well limited, with regular contours, respecting the bone cortex (Figure 1).
MRI of the left knee in T1 sagittal section, T2 sagittal and axial sections and T1 sagittal section after injection of gadolinium showing the presence opposite the anterior tibial tuberosity, a mass at the expense of the saphenous nerve with eccentric development, lateralized on the right, oval, appears encapsulated, in T1 isosignal (compare to the muscle) in heterogeneous T2 hyper signal, intensely and heterogeneously enhanced after injection of gadolinium, containing cystic areas, associated with a discreet infiltration of the peri lesion fat, without involvement of the bone structures in front of it, evoking first a schwannoma of the infra patellar ramus of the saphenous nerve.
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T1 isosignal (compared to muscle) heterogeneous T2 hyper signal, intensely and heterogeneously enhanced after injection of gadolinium measuring 50 mm x 44 mm x 20 mm, containing cystic areas and seems to continue upwards with a nerve structure with eccentric development, associated with a discret infiltration of the peri lesion fat, without involvement of the bone structures in front of it evoking at first a schwannoma of the infra patellar branch of the saphenous nerve, given the eccentric development of the tumor in relation to the nerve fibers (Figure 2). The patient underwent surgery, a total intracapsular excision of the lesion was performed preserving the saphenous nerve.
(A) Spindle cell tumor made of short intersecting bundles (HE x 100) and (B) tumor cells are monomorphic neuroid in appearance showing a palisading arrangement in places (HE x 200).
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The tumor cells are monomorphic without mitotic activity and adopt a pallissadic arrangement with the formation of Verocay nodules (Figure 3) confirming the diagnosis of a schwannoma.