Temporal lesions

Elna-Marie Larsson, Feb 2005

COMMON TUMOURS AND TUMOURLIKE LESIONS IN THE MIDDLE CRANIAL FOSSA

Arachnoid cyst:

  • Intra-arachnoid CSF-filled sac that does not communicate with ventricular system.
  • 50 – 60% located in middle cranial fossa.
  • CT: CSF density, may expand, thin or remodel adjacent skullbone.
  • MRI: Isointense with CSF on T1 and T2, as well as on FLAIR (compare epidermoid cyst with lack of signal suppression on FLAIR).
  • No enhancement.
  • Adjacent temporal lobe may be hypoplastic

Glioblastoma multiforme:

  • WHO grade 4
  • Most common locations are frontal, temporal and parietal lobes.
  • CT and MRI: Irregular contrast enhancement surrounding central necrosis, hemorrhagic portions are not uncommon, peritumoural vasogenic oedema.

Primary CNS lymphoma:

  • Most common in frontal and parietal lobes, often growth along ventricles including temporal horns of lateral ventricles.
  • CT and MRI: Often strongly homogeneously enhancing tumour with mild surrounding oedema, in immunocompromised patients peripheral enhancement with central necrosis may be seen.

Ganglioglioma:

  • WHO grade 1 or 2
  • Most common in superficial hemispheres and temporal lobes.
  • Most common neoplasm causing chronic temporal lobe epilepsy.
  • Well differentiated, slowly growing neuroepithelial tumour.
  • CT and MRI: Often partially cystic, enhancement is seen in approximately 50% (solid, rim or nodular enhancement), calcification common (35 – 50%), superficial lesion may expand cortex and remodel bone, cortical dysplasia may be associated.

DNET (Dysembryoplastic neuroepithelial tumour):

  • WHO grade 1
  • Temporal lobe (often amygdala – hippocampus) most common location.
  • Benign, focal, intracortical mass superimposed on background of cortical dysplasia.
  • Intracortical mass scallops inner table of skull and “points” towards ventricle.
  • CT: Wedge-shaped low density lesion, sometimes difficult to detect, calcification in 20 %, usually non-enhancing.
  • MRI: Pseudocystic multinodular, hypointense on T1, hyperintense on T2, no peritumoural oedema. May have mixed signal with bright rim on FLAIR.

Pleomorphic xantoastrocytoma:

  • WHO grade 2
  • Temporal lobe most common location.
  • Usually benign, found almost exclusively in young adults, often long-standing temporal lobe epilepsy.
  • Peripherally located mass often involving cortex and meninges.
  • CT and MRI: Cystic/solid tumour, moderate/strong enhancement, enhancing nodule often adjacent to to surface of brain, enhancement of adjacent meninges (dural tail) common.

Low grade diffuse astrocytoma:

  • WHO grade 2.
  • Located in temporal lobes in 1/3 of cases.
  • CT: Ill-defined homogeneous hypodense/isodense tumour, calcification in 20%, usually no enhancement.
  • MRI: Hypointense on T1 and homogeneously hyperintense on T2, may appear circumscribed but often infiltrates adjacent brain, may expand adjacent cortex.

Limbic encephalitis:

  • Paraneoplastic syndrome (remote neurological effect of cancer associated with extra-CNS tumour), most often associated with small cell lung carcinoma.
  • CT normal in most cases.
  • MRI: Hyperintensity on T2 and hypointense on T1 in mesial temporal lobes (hippocampus, amygdala), can also be seen in whole limbic system, may have minimal mass effect, patchy enhancement common.

Literature Metastases and Temporal lesions

Elna-Marie Larsson, Feb 2005

Osborn AG et al: Diagnostic Imaging: Brain
W.B. Saunders Company, 2004

ISBN: 0721629059

Osborn AG: Pocket Radiologist: Brain. Top 100 Diagnoses.
Saunders, 2002

Grossman RI, DM Yousem: Neuroradiology: The Requisites (Requisites in Radiology)
C.V. Mosby; 2nd ed., 2003
ISBN: 032300508X

Metastases

Elna-Marie Larsson, Feb 2005

INTRACRANIAL METASTASES

Facts:

Metastases account for up to 50% of all brain tumours and are found at autopsy in 25% of patients with systemic cancer.

The primary tumours that most commonly spread to the brain parenchyma are lung cancer, breast carcinoma, melanoma, renal carcinoma and gastrointestinal tumours. In 10% the primary tumour is unknown. 50% have a solitary metastasis, 20% have two and 30% have three or more lesions. Haemorrhagic metastases are more common in renal carcinoma, melanoma, thyreoid and breast carcinoma, as well as choriocarcinoma. Cystic or calcified metastases favor lung, breast and gastrointestinal primary sites.

Hematogeneous spread is common for metastases in the brain parenchyma. Direct tumour extension can occur from the calvarium to the dura, e.g. in prostatic carcinoma, directly through the skull-base, via foramina and fissures, e.g. in nasopharyngeal carcinoma or via perineural or perivascular tumour growth. Metastatic spread within the brain from a primary CNS-neoplasm, most often glioblastoma multiforme, also occurs. Tumours with CSF-seeding are listed in the table below.

Tumours with CSF seeding

CNS primary / Non CNS primary
Adults:
Glioblastoma multiforme
Oligodendroglioma
Lymphoma
Children:
Choroid plexus papilloma
Ependymoma (blastoma = PNET)
Malignant astrocytoma
Medulloblastoma (PNET)
Pineal region tumours
Retinoblastoma / Adults:
Breast
Gastrointestinal
Genitourinary
Leukemia
Lung
Lymphoma
Melanoma
Children:
Neuroblastoma
Leukemia
Lymphoma

Imaging findings:

  • Relatively well defined tumours with enhancement and moderate – extensive surrounding oedema, some metastases are small without oedema.
  • Characteristic location is the gray/white matter interface.
  • Punctuate, solid or ring-enhancement.
  • CT: iso- or hypodense mass.
  • MRI: iso-/hypointense on T1, hyperintense on T2, haemorrhagic lesions and melanotic melanoma may be hyperintense on T1.
  • Dural metastases may be seen as extension from adjacent bone metastases or isolated to the dura (hematogeneously disseminated), focal contrast enhancing mass is more common than diffuse meningeal thickening with enhancement.
  • Subarachnoid (CSF) seeding is seen as tiny nodules of implanted tumours along the meninges and/or diffuse meningeal enhancement. Enhancement may also be seen along the cranial nerves. MR is much more sensitive than CT. Secondary hydrocephalus may be present.
  • Metastases may sometimes be seen as pineal, pituitary or choroid plexus mass.

Imaging recommendations:

  • Contrast-enhanced MRI has higher sensitivity than contrast-enhanced CT.
  • Double or triple contrast dose MRI increases sensitivity and may be valuable for assessment of operability of solitary metastases (detection of multiple metastses may cancel surgery).
  • Contrast-enhanced MRI is the modality of choice for detection of dural metastases and subarachnoid seeding.

Differential diagnosis:

  • Abscess.
  • Other inflammatory lesions, including demyelinating disease.
  • Primary neoplasm, e.g. glioblastoma multiforme.
  • Resolving hematoma.

SPINAL INTRADURAL METASTASES

  • Intramedullary metastases are rare.
  • MRI with contrast-enhancement is imaging modality of choice.
  • Intramedullary metastasis: well marginated contrast-enhancing focal lesion, may have surrounding oedema.
  • CSF seeding: intradural enhancement (often nodular) including spinal cord surface and cauda equina.