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Pseudoprogression (PsP)


KEY FACTS

Terminology

  • Treatment-related increase in contrast enhancement mimics tumor progression

  • Classically described after treatment with chemoradiation (temozolomide with radiation therapy)

  • Typically occurs within 3-6 months after conclusion of radiation therapy (XRT)

Imaging

  • New enhancing lesion + ↑ FLAIR hyperintensity in treated malignant glioma at 3-4 months after XRT completion

  • T2/FLAIR: Increased hyperintensity with mass effect

  • DWI: Higher ADC values in PsP compared with tumor

  • DSC MR

    • Lower mean rCBV values in PsP compared with tumor

  • DCE MR

    • Mean K trans (volume transfer constant) is lower in PsP compared with true progression

  • MRS: No significant elevation of choline in PsP

  • Best imaging: Contrast-enhanced MR, DWI, ± MRS, MRP

  • Follow-up studies may be necessary to make accurate diagnosis of PsP

  • Knowing clinical history and timing of therapy is key to accurate brain tumor imaging

Top Differential Diagnoses

  • Recurrent malignant glioma

  • Radiation necrosis

Clinical Issues

  • Current standard of care for malignant gliomas is surgical resection followed by concurrent XRT and chemotherapy with temozolomide (Temodar)

    • PsP occurs in ~ 35-50% of patients

  • PsP is self-limited, enhancing lesions resolve without new treatment

  • PsP has been associated with improved survival

  • Important to recognize that not all new enhancement in patient with treated glioblastoma is progressive tumor

Axial T1 C+ MR in a 48-year-old man treated with radiation therapy and Temodar for 3 months for his malignant glioma shows new enhancement
in the frontal lobes bilaterally. His initial postoperative MR study showed no enhancement. He was clinically doing well.

Axial T1 C+ MR in the same patient 4 weeks later shows a marked decrease in the enhancement
without a change in therapy. Imaging findings are related to pseudoprogression, not true progression, likely related to an inflammatory response.

Axial T1 C+ MR in a 62-year-old woman with a multifocal glioblastoma treated with Temodar and radiation therapy shows new enhancement
in the hemispheres on her 4-month scan, concerning for progressive tumor.

Axial T1 C+ MR in the same patient 8 weeks later with no therapy change shows a marked decrease in the enhancing lesions
. The new enhancement was related to pseudoprogression, which is associated with an increased survival.

TERMINOLOGY

Abbreviations

  • Pseudoprogression (PsP)

Synonyms

  • Treatment-related enhancement

  • Treatment-related changes

Definitions

  • Treatment-related increase in contrast enhancement mimicking tumor progression

    • Classically described after treatment with chemoradiation (temozolomide with radiation therapy)

  • Typically occurs within 3-6 months after conclusion of radiotherapy (XRT)

  • Self-limited, enhancing lesions resolve without new treatment

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