Download Skull Base Imaging for Radiation Oncologists

Diagnostic Imaging Findings After
Radiation Therapy for Skull Base
Region Tumors
Daniel Thomas Ginat MD, MS Department of Radiology
James M. Melotek MD
Department of Radiation Oncology
Daniel Haraf MD
Department of Radiation Oncology
EdE-57
Disclosures
None
Please email Daniel Ginat at
[email protected] with questions or
comments.
Introduction
• Radiation oncology plays an important role in the
treatment of nasopharynx and skull base carcinomas.
• Expected findings and complications will be
reviewed, including recurrent tumor and metastases,
radiation-induced necrosis, radiation-induced
neoplasms, optic neuropathy, and Eustachian tube
dysfunction.
• In addition, the role of diffusion weighted imaging
and perfusion MRI, as well as PET will be discussed.
Critical Anatomic Landmarks for
Radiation Treatment Planning
Brainstem: Sagittal T1weighted MRI shows a
squamous cell
carcinoma with skull
base invasion (*) and
epidural extension
abutting the brainstem.
Optic Nerve: Coronal fat
suppressed postcontrast T1-weighted
MRI shows a squamous
cell carcinoma in
proximity to the left
optic nerve (arrow).
Carotid Artery: Coronal
T2-weighted MRI shows
a squamous cell
carcinoma with skull
base invasion that
encases the left internal
carotid artery (arrow).
Critical Anatomic Landmarks for
Radiation Treatment Planning
• Radiation dose limits for selected
critical structures in the skull base
region:
– Brainstem: Up to 54 Gy
– Optic Apparatus: Up to 54 Gy
– Temporal Lobes: Up to 60 Gy
• In general, MRI is the best modality
for the assessment of these
structures.
Radiation therapy isodose
lines in a patient with T4
nasopharyngeal
carcinoma illustrate
planning difficulties.
Locoregional Failure versus Success
Axial fat-suppressed post-contrast T1
MRI show an mass in the right lateral
nasopharyngeal recess at the site of a
treated nasopharyngeal carcinoma
treated 10 years before.
Follow up axial fat-suppressed postcontrast T1 MRI shows development of
necrosis in the tumor following
radiation therapy.
Locoregional Failure versus Success
• Locoregional failure is the predominant pattern of
relapse following non-surgical treatment and includes
in-field and marginal recurrence patterns.
• This may relate to intrinsic radioresistance or factors
such as tumor hypoxia.
• Methods to intensify locoregional treatment include
chemotherapy, biological therapies, radiosensitizers,
altered fractionation, and dose escalation.
• Diffusion-weighted imaging, perfusion-weighted
imaging, and FDG-PET may be useful for characterizing
post-treatment status.
Diffusion Weighted Imaging
Adenoid cystic carcinoma
Before and after treatment.
Diffusion Weighted Imaging
• Water molecules within intact cell membranes of viable
tumor cells are characterized by a relatively small mean freepath length, which results in restricted diffusion and low ADC
values.
• On the other hand, tumor necrosis is characterized by
increased membrane permeability and breakdown of the cell
membrane, resulting in free diffusion and increased mean
free-path length of diffusing molecules.
• These changes result in decreased restriction and thereby
increased diffusion of water molecules in the necrotic regions.
• DWI can potentially assist in selecting the site for biopsy.
Perfusion Weighted Imaging
Treated Tumor
Versus
Viable Tumor
Enhancing tissue in the treated
left nasopharyngeal region
does not show corresponding
high blood volume, consistent
with non-viable tumor (arrows).
Enhancing mass in the
central skull base shows
corresponding high blood
volume, consistent with
viable tumor (arrows).
Perfusion Weighted Imaging
• Dynamic contrast-enhanced (DCE) MRI is a
non-invasive technique that can provide
anatomical and physiological information
about tumors.
• Areas of persistent enhancement in the
treatment bed can mimic tumor.
• The presence of low blood volume suggests
treatment effects, while elevated blood
volume suggests persistent tumor.
18FDG-PET
“True Positive” “False Positive”
Tumor Recurrence Inflammation
“False Negative”
Adenoid cystic
carcinoma
18FDG-PET
• Although very useful for staging and cases with
unknown primaries, 18FDG-PET has several
limitations, particularly in the first 3 months after
treatment.
• False positive results: Inflammation and infection
in particular can mimic tumor.
• False negative results: Small tumors may have
inconspicuous hypermetabolism and certain
tumors, such as adenoid cystic carcinoma and
highly necrotic tumors, may have inherently low
metabolic activity.
Perineural Tumor Spread
The patient has a history of right submandibular adenoid cystic carcinoma.
Axial CT shows widening of the right foramen ovale (arrow). Axial and
coronal fat-suppressed post-contrast MR images show expansion and
enhancement of the right trigeminal nerve (arrows).
Perineural Tumor Spread
• Can be a manifestation of out-of-field treatment
failure.
• Adenoid cystic carcinoma has a strong tendency for
perineural tumor spread at presentation, but is most
commonly encountered with cutaneous squamous
cell carcinomas.
• The facial and trigeminal nerves are most commonly
involved.
• Imaging findings: thickened nerves with abnormal
enhancement, foraminal widening, and obliteration
of surrounding fat.
Leptomeningeal Carcinomatosis
The patient has a history of small cell neuroendocrine carcinoma of the
nasopharynx with extension into the skull base, treated with
cisplatin/etoposide and concurrent radiotherapy. Axial post-contrast T1weighted MR images show scattered areas of leptomeningeal enhancement,
including along the cranial nerves.
Leptomeningeal Carcinomatosis
• Rare form of metastatic disease that can manifest
even after treatment of certain head and neck
carcinomas, such as those of neuroendocrine
origin.
• May be overlooked or inapparent on routine posttreatment head and neck CTs.
• Entire neuraxis MRI with contrast and
cerebrospinal fluid analysis is necessary for
diagnosis.
• Portends a poor prognosis.
Radiation-Induced Neoplasms
The patient has a history of right maxillary sinus squamous cell carcinoma in
treated with radiation therapy (61.2 gray in 1.9 gray fractions) 20 years earlier
and presents with right vision loss. MRI depicts an enhancing right skull base
mass (arrows), including within the cavernous sinus and optic canal. The tumor
proved to be a spindle cell sarcoma.
Radiation-Induced Neoplasms
• Radiation-induced tumors most commonly arise at
the margins of the radiation field, where the dose is
not high enough to decimate tissues, but high
enough to be carcinogenic.
• The most common types of neoplasms include soft
tissue sarcomas, squamous cell carcinomas, and
salivary gland tumors.
• The development of radiation-induced neoplasms is
delayed, with a mean duration from radiotherapy
until the diagnosis of cancer is 13 years; therefore,
long-term follow up is warranted.
Dural Reaction
Axial and coronal post-contrast fat-suppressed T1-weigheted MR images show an
esthesioneuroblastoma with orbital and epidural extension. There is also diffuse mild
right cerebral convexity dural thickening and enhancement (arrows).
Dural Reaction
• Should not be confused with actual neoplastic
involvement and lead to an unnecessarily high
radiation field.
• “Dural tail” presumed to represent hypervascular
tumor reaction.
• Criteria:
– Should be identified on two successive sections through
the tumor.
– Should taper smoothly away from the tumor.
– Must enhance more than the tumor itself.
Skull Base Remineralization
Initial scan
Axial CT image shows extensive
skull base erosions associated
with a nasopharyngeal
carcinoma.
One year later
Follow up axial CT image shows
near-anatomical
remineralization of the
previously affected skull base.
Skull Base Remineralization
• After radiation for nasopharyngeal carcinoma, 23%
have sclerosis or bony regeneration in the skull base
• Sclerosis in 28% of these transforms into
osteoporosis 1 to 5 years afterwards.
• The appearance of osteolytic changes in the skull
base during follow-up of patients with
nasopharyngeal carcinoma who had normal skull
base morphology before treatment is associated with
tumor recurrence.
Skull Base Osteomyelitis
The patient has a history of nasopharyngeal
carcinoma treated with radiation. The MR
images show edema and enhancement in the
bone marrow of the central skull base with
relatively elevated diffusivity.
Skull Base Osteomyelitis
• Patients with head and neck carcinomas may be
prone to infections at the treatment sites.
• The signal characteristics, enhancement, and an
infiltrating pattern can be indistinguishable from
neoplastic processes on MRI.
• Diffusion-weighted MRI ADC values of skull base
osteomyelitis are often significantly higher than
with nasopharyngeal carcinoma and lymphoma.
Osteonecrosis
The patient has a history of recurrent nasopharyngeal carcinoma treated with
chemoradiation. The patient also required dental extractions , which where complicated by
osteoradionecrosis of the right mandible. Axial and coronal CT images show an irregular
lytic process in the right mandible adjacent to the extraction sites (arrows).
Osteonecrosis
• Most commonly involves the mandible, particularly
following dental extractions, and may be
pharmaceutical and/or radiation induced.
• Appears as a lytic process sometimes associated with
pathological fracture, soft tissue swelling,
enhancement, and hypermetabolism on FDG-PET,
which can mimic tumor.
• Biopsy can exacerbate the patient symptoms.
Nasopharyngeal Necrosis and Carotid
Blow Out Syndrome
The patient has a history of right nasopharyngeal carcinoma. The
pretreatment contrast-enhanced CT image shows an enhancing mass in
the right nasopharynx with extension into adjacent spaces. The patient
subsequently developed hemoptysis and CT shows hemorrhage in the
treatment bed (arrow). Follow up CT image shows a large defect at the
site of the tumor due to extensive soft tissue necrosis.
Nasopharyngeal Necrosis and Carotid
Blow Out Syndrome
• Late complication of radiation therapy for
nasopharyngeal carcinoma.
• Imaging can show edematous soft tissues that can
slough and then lead to soft tissue deficiencies.
• Carotid blow-out refers to rupture of the carotid
artery and its branches and is predisposed by vessel
exposure from tumor.
• Angiography may demonstrate pseudoaneurysm
formation or even frank contrast extravasation,
often associated with deficient soft tissue.
Temporal Lobe Necrosis
2 years later
History of right nasopharyngeal lymphoepithelioma.
The initial axial T2-weighted MRI shows a
hypointense mass in the right nasopharynx. Follow up
brain FLAIR and post-contrast T1-weighted MR
images show extensive anterior right temporal lobe
edema and ring-enhancement.
Temporal Lobe Necrosis
• Debilitating late complication of radiation therapy for
nasopharyngeal cancer.
• The location and timing are highly suggestive of brain
necrosis.
• However, ring enhancement and edema can mimic
neoplasm.
• Associated hemorrhage is occasionally observed as
well.
• PET and MR perfusion can help differentiate necrosis
from tumor if otherwise uncertain, whereby there is
decreased metabolic activity and hypoperfusion.
Optic Neuropathy
The patient was treated
with radiation for adenoid
cystic carcinoma invading
the left cavernous sinus
(encircled). The left optic
nerve was normal initially.
The patient subsequently
developed left visual acuity
deficits. MRI demonstrated
hyperintensity of the left
optic nerve without
significant enlargement
(arrow).
2 years later
Optic Neuropathy
• Radiation optic neuropathy causes rapid
deterioration over days to weeks.
• Likely result from vascular endothelial injury
and related to total dose and daily
fractionation size.
• The affected nerve may display diffuse T2
hyperintensity and/or focal enhancement and
remain normal in size or become slightly
enlarged.
Eustachian Tube Dysfunction
The patient has a history
of left nasopharyngeal
carcinoma treated with
radiation and presented
with post-treatment left
hearing loss. Axial T2weighted MRI shows
effusions within the left
mastoid air cells, middle
ear, and part of the
Eustachian tube (arrow).
Eustachian Tube Dysfunction
• Eustachian tube edema and secretory otitis media
are the main cause of conductive hearing loss in
early stages and is mostly reversible.
• Tumor regression following radiotherapy is the
main factor leading to improvement in Eustachian
tube function, but scarring can lead to persistent
dysfunction after treatment.
• On imaging, fluid within the involved mastoid air
cells, middle ear, and a portion of the Eustachian
tube is commonly observed.
Selected References
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Complications of radiation therapy for head and neck cancers. The
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• Oksuz DC, Prestwich RJ, Carey B, Wilson S, Senocak MS, Choudhury A,
Dyker K, Coyle C, Sen M. Recurrence patterns of locally advanced head
and neck squamous cell carcinoma after 3D conformal (chemo)radiotherapy. Radiat Oncol. 2011 May 24;6:54.
• Saito N, Nadgir RN, Nakahira M, Takahashi M, Uchino A, Kimura F,
Truong MT, Sakai O. Posttreatment CT and MR imaging in head and
neck cancer: what the radiologist needs to know. Radiographics. 2012
Sep-Oct;32(5):1261-82; discussion 1282-4.
• Offiah C, Hall E. Post-treatment imaging appearances in head and neck
cancer patients. Clin Radiol. 2011 Jan;66(1):13-24.