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Parapharyngeal Space Benign Mixed Tumor


KEY FACTS

Terminology

  • Parapharyngeal space benign mixed tumor (PPS-BMT): BMT is primarily in PPS, not extension of deep lobe parotid BMT into PPS

Imaging

  • Rounded, well-defined ovoid lesion within PPS fat

    • Distinct from parotid deep lobe

  • CECT findings

    • Heterogeneous, moderately enhancing PPS mass

  • MR findings

    • Fat plane between deep lobe parotid & PPS-BMT

    • T1 C+ MR: Uniform enhancement when small

      • –

        Heterogeneous enhancement when large

    • T2 MR: Marked T2 hyperintensity similar to CSF

Top Differential Diagnoses

  • BMT of parotid deep lobe

  • Pterygoid venous plexus asymmetry

  • Neurogenic tumor in PPS

Pathology

  • Rare lesion; much more common than parotid deep lobe BMT

  • Benign tumor arising in aberrant salivary gland rests in PPS

  • Solid but often heterogeneous with hemorrhage, cystic degeneration, or necrosis

  • Occasional ossific or calcific degeneration

Clinical Issues

  • Most asymptomatic, or minimally so, because of deep location and slow growth

  • Small lesion usually incidental imaging finding

  • Surgery: Typically cervical-parotid approach, occasionally with mandibulotomy

    • Resection without violation of tumor capsule is critical to prevent recurrence, often multifocal

    • ± total parotidectomy with facial nerve preservation

Axial CECT demonstrates a well-defined, benign mixed tumor (BMT)
within the left parapharyngeal space. The lesion is completely surrounded by parapharyngeal space (PPS) fat separating it from pharyngeal mucosal space medially
, parotid deep lobe laterally
, and carotid space posteriorly
.

Axial T1WI MR reveals a well-defined PPS BMT within the right deep face
, completely surrounded by parapharyngeal fat. Note the mass is separated from the deep parotid by PPS fat
.

Coronal T1WI MR shows a well-defined BMT
to be surrounded by high-signal parapharyngeal fat. The mass is too small to have mass effect on adjacent tissues and was incidentally found on brain MR. There is normal PPS fat
on the left.

Axial T2WI FS MR shows homogeneous hyperintensity of a slightly lobulated PPS BMT
. Hyperintensity similar to CSF is typically seen with BMTs, although postcontrast images confirm it to be a solid mass (not shown).

TERMINOLOGY

Abbreviations

  • Parapharyngeal space, benign mixed tumor (PPS-BMT)

Synonyms

  • Pleomorphic adenoma of PPS

Definitions

  • Benign tumor arising from aberrant minor salivary gland rests in PPS

  • Surgeons often describe lesions as "parapharyngeal," whether arising in PPS proper, parotid deep lobe, pharyngeal mucosal space or masticator space

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