Petrous Apex Lesion

Petrous Apex Lesion
Logan A. McLean, MD & H. Ric Harnsberger, MD
DIFFERENTIAL DIAGNOSIS
Common
  • Asymmetric Marrow, Petrous Apex
  • Trapped Fluid, Petrous Apex
  • Cholesterol Granuloma, Petrous Apex
  • Primary or Metastatic Disease
Less Common
  • Cephalocele, Petrous Apex
  • Meningioma, T-Bone
  • Fibrous Dysplasia, T-Bone
  • Schwannoma, Trigeminal, Skull Base
  • Cholesteatoma, Petrous Apex
  • Chondrosarcoma, Skull Base
  • Langerhans Histiocytosis, Skull Base
  • Apical Petrositis
  • Mucocele, Petrous Apex
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
  • Best imaging tool
    • CT and MR are complementary
      • Bone CT to evaluate petrous apex (PA) “bony” expansion or destruction
      • MR for lesion tissue analysis; characteristic signal per diagnosis
  • Beware confusing high T1 MR signal in trapped fluid with PA cholesterol granuloma
    • When protein content is high, T1 signal may be high
    • In absence of bony expansion on CT, lesion should be considered trapped fluid
Helpful Clues for Common Diagnoses
  • Asymmetric Marrow, Petrous Apex
    • Asymmetric pneumatization makes contralateral fatty marrow conspicuous
    • CT findings
      • Nonexpansile fat density PA
    • MR findings
      • High T1 normal fatty marrow
  • Trapped Fluid, Petrous Apex
    • Remote otomastoiditis leaves behind PA air cell fluid of variable protein content
    • CT findings
      • Opacified air cells, trabeculae present
    • MR findings
      • Low T1, high T2 signal
  • Cholesterol Granuloma, Petrous Apex
    • Chronic otitis media; pneumatized PA with recurrent hemorrhage
    • CT findings
      • Smooth, expansile margins
      • Larger lesions affect clivus, jugular tubercle, ICA
    • MR findings
      • High T1 and T2 signal in expanded PA
  • Primary or Metastatic Disease
    • Rhabdomyosarcoma (primary or mets), neuroblastoma
    • Metastasis occurs late in the disease process
      • Dx of primary disease is usually known
    • Radiographic appearance is variable
Helpful Clues for Less Common Diagnoses
  • Cephalocele, Petrous Apex
    • Incidental PA lesion where Meckel cave appears herniated into subjacent PA
    • CT findings
      • Expansile ovoid lesion
    • MR findings
      • Low T1, high T2 “pseudopod” from Meckel cave to PA; nonenhancing
  • Meningioma, T-Bone
    • CT findings
      • Permeative
      • Sclerotic or hyperostotic bony changes
    • MR findings
      • Dural-based mass invades PA with avid contrast-enhancement, dural tail
  • Fibrous Dysplasia, T-Bone
    • Bone disorder of younger women (< 30 years) with progressive replacement of normal marrow by mixture of fibrous tissue and disorganized trabeculae
      • Active phase: Cystic
      • Least active/burned out: Sclerotic
    • CT findings
      • Expansile bone lesion with mixed ground-glass/sclerotic and cystic components sparing otic capsule
    • MR findings
      • Low T1 and T2 signal, foci of enhancement common
  • Schwannoma, Trigeminal, Skull Base
    • Larger trigeminal nerve schwannoma involves preganglionic segment as it passes into Meckel cave
    • CT findings
      • Smooth PA remodeling of inferior porus trigeminus margin
    • MR findings
      • Homogeneously enhancing tubular mass
      • Intramural cysts when large
  • Cholesteatoma, Petrous Apex
    • Congenital or acquired PA cholesteatoma
    • CT findings
      • Smooth, expansile, low-density lesion
    • MR findings
      • Low T1, high T2
      • Nonenhancing PA lesion with restricted diffusion on DWI
  • Chondrosarcoma, Skull Base
    • Originates from petrooccipital fissure
    • CT findings
      • Characteristic chondroid matrix in 50%, invasive bony changes
    • MR findings
      • T2 high signal, mixed enhancement
  • Langerhans Histiocytosis, Skull Base
    • Langerhans histiocytes proliferation forming lytic sites in skull and skull base
    • Peds
      • Onset at 1 year; multifocal < 5 years
    • CT findings
      • Lytic lesion with beveled margins
    • MR findings
      • Avidly enhancing soft tissue mass
  • Apical Petrositis
    • Fever, retroorbital pain, diplopia, otorrhea
    • CT findings
      • Bony destructive changes
    • MR findings
      • Enhancing thick dura, PA pus does not enhance
  • Mucocele, Petrous Apex
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Aug 10, 2016 | Posted by in PEDIATRICS | Comments Off on Petrous Apex Lesion

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