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malignant peripheral nerve sheath tumors ( mpnsts ) are a rare variety of soft - tissue sarcoma of ectomesenchymal origin , with an estimated incidence of 0.1/100,000/year . recently ,
fluorodeoxyglucose ( fdg ) positron emission tomography / computed tomography ( pet / ct ) has been employed in differentiating the malignant from the benign peripheral nerve sheath tumors .
the current case highlights an unusual pet / ct presentation of mpnst masquerading clinically as infected dermatoses .
a 64-year - old male , working as a gardener , presented with multiple rapidly progressive asymptomatic skin colored raised lesions 2 - 4 cm in diameter , over the medial border of the right foot and lower part of the right leg since 1 month .
the lesion was subjected to punch biopsy , with clinical differential diagnosis of sporotrichosis , actinomycetoma , linear cutaneous leishmaniasis and atypical mycobacterial infection .
histopathology revealed a malignant mesenchymal tumor , which was confirmed to be a mpnst on immunohistochemistry .
soon thereafter , the lesions rapidly increased in size and number and began to ulcerate and become painful [ figure 1a ] . magnetic resonance imaging ( mri ) of the right lower limb revealed multiple enhancing nodular lesions seen involving the skin and subcutaneous tissue .
subsequently , a whole body 18f - fdg pet / contrast - enhanced computed tomography ( cect ) scan was performed on a whole body full ring pet / ct camera ( discovery ste 16 , ge ) .
370 mbq of 18f - fdg was administered intravenously subsequent to a 6 h fast .
whole body cect scan was performed after intravenous instillation of non - ionic contrast medium . after the ct scan
, an emission scan was performed from head to thigh for 2 min per frame .
images were reconstructed by 3d vue algorithm ( ge ) and viewed on a xeleris workstation ( ge ) using the volumetric protocol .
the study revealed multiple fdg avid nodular lesions ( maximum standardized uptake value 18.6 ) in the right lower limb [ figure 1b ] , which were many more in number compared with those picked up on cutaneous examination .
multiple nodular lesions ( arrows ) with evidence of ulceration on the medial aspect of the right leg and foot ( a ) , which show increased fluorodeoxyglucose avidity ( b ) mpnsts arise from a peripheral nerve or its branches or from the nerve sheath .
although they may arise spontaneously , up to 50% arise in patients of neurofibromatosis 1 ( nf1 ) .
mri is the imaging modality of choice because it can reveal the nerve of origin and its relationship to adjacent structures .
although it is well - known that these tumors can extend for considerable distances along nerves , it may not always be possible to delineate the origin from the nerve .
a recent study by bilgic et al . has shown that the nerve origin could be identified only in 45 - 56% cases .
there have been recent reports of fdg pet / ct in mpnst , most of which have been performed in patients with nf1 .
it has been documented as a useful tool in monitoring clinically stable nf1 patients with plexiform neurofibromas as it could predict which were more likely to subsequently grow rapidly .
it has also been found that in patients with nf1 harboring mpnsts ; higher fdg uptake is associated with poorer survival rates .
in addition , it can assist in guiding targeted needle core biopsies and may provide critical information in tumors that are not amenable to biopsy .
it thus plays an important role in the staging , restaging and post - therapy follow - up of mpnst in nf1 .
a high fdg uptake has been documented in sporadic mpnsts also , as is well seen in the coronal maximum intensity projection image [ figure 2 ] in the present case .
coronal maximum intensity projection image showing high fluorodeoxyglucose uptake in multiple nodular lesions on the right lower limb , predominantly on the medial aspect mpnsts usually present as discrete masses , which may be multifocal , especially in cases of nf1 .
the present case was unusual in its presentation , owing to the linear arrangement of multiple nodules over the lower extremity in a gardener , raising the possibility of infectious dermatoses .
these multiple hypermetabolic mildly enhancing nodular lesions were restricted to the skin and subcutaneous tissue with no extension into the underlying muscles [ figure 3 ] .
the additional lesions detected on pet / ct were also proven to be mpnst based on histopathology with immunocytochemistry [ figure 4 ] .
though multimodality therapy , including surgical resection and adjuvant radiotherapy , is available , the prognosis remains dismal .
axial contrast - enhanced computed tomography ( a ) and fused positron emission tomography / computed tomography ( b ) images of the leg ( upper row ) and foot ( lower row ) demonstrate multiple hypermetabolic mildly enhancing nodular lesions ( arrows ) involving the skin and subcutaneous tissue with no extension into the underlying muscles ( a ) h and e stain ( 10 [ inset  40 ] ) shows a tumor in the dermis with multiple spindle - shaped cells in whorls with pleomorphic nuclei forming a storiform pattern .
( b ) vimentin stain ( 10 [ inset  40 ] ) for mesenchymal structures is diffusely positive throughout the dermis
malignant peripheral nerve sheath tumors ( mpnsts ) are rare tumors , with an estimated incidence of 0.1/100,000/year . 
 they are regarded as a rare variety of soft - tissue sarcomas that derive from peripheral nerves or from cells associated with the nerve sheath . until 50% of observed mpnsts occur in patients with neurofibromatosis 1 ( nf1 ) . 
 the typical presenting signs and symptoms of a pnst are a palpable mass involving a peripheral nerve , loss of nerve function and/or pain . 
 recently , positron emission tomography ( pet ) has been used to detect 18f - fluorodeoxyglucose uptake in these tumors . 
 most of the pet studies have been reported in patients with nf1 . 
 we report a case of sporadic mpnst masquerading as infectious dermatoses , with an unusual pet / computed tomography presentation .