The more you look the more you find: imaging observations of lumbosacral Malignant Peripheral Nerve Sheath Tumor

Clinical History

A 23 year old male patient, practicing martial arts, presented complaining of a huge mass in the lumbosacral region [Figure 1], which gradually increased in size. No history of anergy, fever, weight loss, surgery, no family story of similar complaint. No café au lait spots identified. Leukocytosis (15.000). Suspected of having abscess.

Imaging Findings

Lumbosacral spine X-ray: no bone lesions but abnormal shadow at level of lumbosacral region (Figure 2).
Precontrast CT: heterogeneous subcutaneous mass of the lumbosacral region, localized in fat planes, having close relations of contiguity with paravertebral and gluteus muscles, of 15 x 6, 5 cm, compatible with hematic material (Figure 3A).
Contrast-enhanced CT: no mass enhancement during post contrast scans (Figure 3B-D).
Ultrasound: well-defined, low echo signal, heterogeneous mass, peripherically hypervascularized (Figure 4).
MRI: T1-weighted scans of isointense mass with contextual nonspecific hyperintense foci (Figure 5A). T2-weighted and STIR images of the slight hyperintense non-specific signal to the periphery of the mass (Figure 5B). Conventional (Figure 6A) and postcontrast THRIVE sequences highlighting the rich peripheral vascularity (Figure 6B, C). SPIR characterised the central foci as haemoglobin catabolites (Figure 6D). DWI persisting high signal intensity with b=1000 correspondent to low ADC apprearances.
Chest CT: No infiltrative pulmonary lesion nor metastatic bone involvement.

Discussion

MPNSTs are rare neoplasms originating from peripheral nerves or from associated cells as Schwann cells, perineural cells, or fibroblasts [1]. Because they can arise from multiple cell types in different locations, the overall appearance can vary greatly from one case to the next. MPNSTs usually present as an enlarging palpable mass and might be asymptomatic. This occurs more often in the setting of Neurofibromatosis type 1(NF1) and should raise concern for malignant degeneration of a neurofibroma. In the differential diagnosis should be considered Malignant Fibrous Histiocytomas and Liposarcoma.
CT and Magnetic Resonance imaging, can provide important information, including the tumor location, its characteristics and its associations with other tissues. MPNSTs share basic imaging characteristics with their benign counterparts such as neurofibromas and schwannomas. These include a fusiform shape, a well defined margins and a longitudinal orientation in the direction of the nerve. Large size (> 5 cm), location and intralesional heterogeneity, as found in this case, are more suggestive of MPNSTs, but no fusiform shape was observed, the lesion appeared horizontally orientated, had smooth margins and contained an amount of intralesional fatty tissue. The tumour showed no contrast enhancement at the CT examination so CT imaging observations in this study were more similar with those of hematoma. Fortunately, in consideration of the uncertain patient’s anamnestic data, we MRI was performed.
Generally, on T1-/T2-weighted MRI, MPNSTs appear iso-/hyper-intense and heterogenous, but they can sometimes have low signal due to the high collagen content in T2W sequences. No ‘fascicular sign’, suggestive for a lesion of neurogenic origin, was found on T2W images, marked peripheral enhancement was demonstrated after contrast and progressive marked centripetal fill-in was observed. The fatty tissue components were identified, the lesion showed no fusiform shape and no nerve input-output relation, which is why a radiological diagnosis of liposarcoma, the most common histological subtype, was considered [2].
The mainstay of treatment is surgical resection.
Imaging studies of the chest are important as MPNSTs are most likely to metastasize to the lungs, bones and pleura. No pleural or bone lesions were found.
CT and MR provide important information about MPNSTs, but in keeping with their insidious vascularization, excellent contrast resolution make MR superior to CT.

Differential Diagnosis List

Final Diagnosis

Malignant Peripheral Nerve Sheath Tumor (MPNST)

URL:	https://www.eurorad.org/case/13086
DOI:	10.1594/EURORAD/CASE.13086
ISSN:	1563-4086