Introduction
There is significant overlap in the imaging appearance and presentation of dural-based mass lesions. The differential diagnosis includes both benign lesions (such as meningioma—WHO grade I) and more aggressive, malignant lesions (such as dural-based metastasis, atypical or malignant meningioma—WHO grade II and III, and lymphoma). Also included are inflammatory pathologies, such as IgG4-related disease (RD) and granulomatous disease (e.g., sarcoid). This chapter reviews several patient case studies of common and important dural-based mass lesions utilizing a structured framework that allows the reader to generate findings and a differential diagnosis. The case outcomes are then presented, and key teaching points are reviewed. An emphasis is placed on imaging and the interpretation of central findings. Treatment considerations are mentioned for continuity of thought, but most diagnoses have dedicated chapters later in this text that cover treatment in greater detail.
Imaging of the meninges
Imaging of the meninges relies primarily on MRI, although CT can provide important information. The meninges are not well visualized normally, so conspicuity on any imaging modality should prompt close evaluation.
When evaluating dural-based lesions, it is helpful to examine not only the appearance of the lesion but also the effect the lesion is having on surrounding structures. For example, a characteristic feature of meningiomas is hyperostosis or infiltration of the adjacent calvarium. Not all meningiomas have this feature (estimated incidence ranges from 4.5–44%), but its presence should weight the differential toward a meningioma and away from other diagnoses. The characteristics of the lesion are, of course, also instructive. The presence of intralesional calcifications can be a feature of meningiomas (occurs in 20–30%). Both of these imaging findings are best appreciated on CT and illustrate why CT can be helpful in the workup for any dural-based lesion.
MRI is most helpful in evaluating for characteristic imaging features of a dural-based lesion, for the full extent of the lesion, and for the effect on the adjacent brain parenchyma. Each MRI imaging sequence provides information about the lesion, which helps rank the differential diagnosis. Although WHO grade I meningiomas are the most common extra-axial dural-based lesion, other pathologic entities such as dural-based metastasis, lymphoma, malignant meningiomas, and granulomatous diseases need to be excluded, as these can be more aggressive and need urgent treatment. Developing a differential diagnosis for a new dural-based lesion is essential, as errors in management can occur if one decides too early that a lesion is a benign meningioma (e.g., WHO grade I).
Clinical pearls for evaluating dural-based lesions
Some rules of thumb to consider when evaluating a new dural-based lesion include:
- 1.
Most are T1 iso-hypointense on MRI. If they are T1 hyperintense, consider etiologies that contain methemoglobin (subacute hemorrhage), high protein, fat, melanin, or calcium.
- 2.
Some dural-based lesions are T2 hyperintense due to high water content. Others are T2 hypointense due to their high cellularity (particularly if the tumor cells have a high nuclear to cytoplasmic ratio, such as lymphoma). Some meningiomas can be fibrous and these have lower T2 signal.
- 3.
Diffusion restriction in dural-based lesions is variable. Diffusion restriction is an evaluation of how freely water molecules can move in a given medium. If restricted diffusion is present, then consider highly cellular tumors, such as lymphoma, cellular meningiomas, or metastases.
- 4.
Enhancement is a product of disruption of the blood–brain barrier. Extra-axial lesions do not have a blood–brain barrier and most avidly enhance. Meningiomas, the most common dural-based neoplasm, typically diffusely and homogeneously enhance. They often have adjacent dural enhancement/thickening, which is referred to as a “dural tail.” Most other dural-based neoplasms also avidly enhance, so the presence of enhancement does not exclude more aggressive neoplasms. If the enhancement pattern is heterogenous, a low-grade meningioma is less likely.
- 5.
Evaluate the relationship of the dural-based lesion with the brain. To establish the lesion is truly extra-axial, look for cerebrospinal fluid (CSF) between the margins of the tumor and the adjacent brain parenchyma (also called a CSF cleft). If there is an indistinct interface between the dural-based mass and the brain or if there is a large amount of edema in the brain, there is a higher likelihood that the mass will be a higher meningioma grade or a more aggressive neoplasm.
Clinical cases
Case . A 61-year-old female presented to the ED with vague constitutional complaints. A CT head was ordered as part of a vertigo workup. She was seen by Neurology 2 weeks later for persistent vertigo and an MRI Brain was ordered.
Imaging findings. CT without contrast demonstrates a partially calcified ( Fig. 5.1 ), extra-axial lesion overlying the left frontal convexity ( Fig. 5.2 ) with extension into the adjacent calvarium and associated hyperostosis ( Fig. 5.1 ). The lesion is isointense to grey matter on T1 ( Fig. 5.3 ). The lesion is heterogeneous on T2 with very dark components consistent with calcification ( Fig. 5.4 ). The lesion is avidly enhancing ( Fig. 5.5 ).
Fig. 5.1
CT without contrast, bone window (3000/700).
Fig. 5.2
CT without contrast, subarachnoid hemorrhage (SAH) window (95/60).
Fig. 5.3
T1 weighted.
Fig. 5.4
T2 weighted.
Fig. 5.5
Volumetric interpolated brain examination (T1 weighted) with contrast.
Primary differential diagnosis.
- 1.
Meningioma
- 2.
Dural-based metastasis
- 1.
Other studies/testing needed or recommended. Follow-up brain MRI with and without contrast in approximately 3 months to document stability.
Referrals to consider. Neurosurgery.
Diagnosis. Incidental meningioma
Treatment considerations. Given the relatively small size of the lesion, absence of edema in the adjacent brain parenchyma, and absence of symptoms that could be attributed to the lesion, treatment should primarily involve observant monitoring with periodic imaging to evaluate for growth. Consider performing initial follow-up imaging with MRI in 3 months given that dural-based metastasis is on the differential. If the lesion is unchanged, follow-up imaging could be performed at 6–12 months and then every year to assess for growth. If there is evidence of interval growth, the patient should be referred for neurosurgical consultation.
What happened in the case presented. Patient received treatment related to probable benign positional vertigo with no specific treatment for the incidental meningioma. Serial follow-up imaging over the last 2 years has demonstrated continued stability of the lesion, making it most compatible with an incidental meningioma.
Teaching Points: Diagnosing an Incidental Lesion as Meningioma Based on Imaging Features. With incidental dural-based masses such as this one, there can be features that strongly suggest that the mass is a meningioma, such as hyperostosis and internal calcifications. However, only follow-up imaging can determine if the mass is almost certainly a benign meningioma (e.g., WHO grade I) rather than a higher-grade meningioma, dural-based metastasis, or other less common dural-based lesions, such as lymphoma or granulomatous disease. If the incidental, asymptomatic lesion is stable on follow-up imaging, it is reasonable to continue to follow the lesion with serial imaging. Alternatively, neurosurgical consultation would also be reasonable (see Chapter 10 for discussion of meningioma management).
Case . A 39-year-old male who presented to an urgent care facility with a chief complaint of a 1-week history of left leg tremors lasting 3–4 minutes, which progressed to numbness the night before. A CT and subsequent MRI were obtained.
Imaging findings. CT with contrast demonstrates a partially calcified ( Fig. 5.6 ), avidly enhancing, extra-axial lesion overlying the right parietal lobe ( Fig. 5.7 ) with extension into the adjacent calvarium and associated hyperostosis ( Fig. 5.6 ). The lesion is iso-hypointense to grey matter on T1 ( Fig. 5.8 ), heterogenous on T2 ( Fig. 5.9 ), and diffusely enhancing with an adjacent enhancing dural tail (arrow) ( Figs 5.10 and 5.11 ).
Fig. 5.6
CT with contrast, bone window (3000/700).
Fig. 5.7
CT with contrast, SAH window (95/60).
Fig. 5.8
T1 weighted.
Fig. 5.9
T2 weighted.
Fig. 5.10
T1 weighted with contrast.
Fig. 5.11
T1 weighted with contrast (coronal).
Differential diagnosis.
- 1.
Meningioma
- 2.
Hemangiopericytoma
- 3.
Dural metastasis
- 1.
Other studies/testing needed or recommended. None.
Referrals to consider.
- 1.
Neurosurgery
- 2.
Potentially radiation Oncology after neurosurgical resection (depending on WHO grade of tumor)
- 1.
Diagnosis. Meningioma (atypical, grade II)
Treatment considerations. Treatment of large meningiomas, particularly those that are symptomatic and demonstrating more aggressive features, is primarily surgical excision with follow-up imaging to monitor for recurrence. If surgical pathology indicates a high-grade tumor, adjuvant external beam radiation should be considered.
What happened in the case presented. Patient underwent right parietal craniotomy and gross-total resection of the meningioma, which he tolerated without complication. Pathology confirmed an anaplastic meningioma (WHO grade II), and the patient was referred to radiation oncology for external beam radiation. At 3-year follow-up, patient has memory and concentration problems, but no evidence of disease recurrence.
Teaching Points: Imaging Features Suggestive of a Higher-Grade Meningioma. As discussed in the previous case, differentiating meningiomas from other dural-based pathology on the initial imaging study can be challenging. The presence of hyperostosis of the adjacent calvarium or intralesional calcifications favor meningiomas. Although this case ultimately turned out to be an anaplastic meningioma, it is not possible to reliably differentiate WHO grade I–III by imaging alone. Invasion of the mass into the adjacent brain is concerning for a higher-grade meningioma (grade II or III), dural-based metastasis, or hemangiopericytoma.
Case . A 45-year-old female presents with 1-year history of progressive painless right-sided vision loss. She also describes some transient symptoms involving the right side of her face and neck.
Imaging findings. Soft tissue mass centered in the right posterolateral orbit extending through the superior orbital fissure into the right cavernous sinus and along the dural margin of the right middle cranial fossa. The lesion is T1 isointense ( Fig. 5.12 ), relatively isointense to grey matter on T2 ( Fig. 5.13 ), and avidly enhances ( Fig. 5.14 ). On CT, there is asymmetric sclerosis and expanded appearance of the right sphenoid bone ( Fig. 5.15 ).
Fig. 5.12
T1 weighted.
Fig. 5.13
T2 weighted.
Fig. 5.14
T1 weighted with contrast.
Fig. 5.15
CT without contrast, bone window (3890/800).
Differential diagnosis.
- 1.
Meningioma
- 2.
IgG4-RD
- 3.
Idiopathic orbital inflammation (Tolosa Hunt)
- 4.
Orbital sarcoidosis
- 5.
Orbital lymphoma
- 6.
Orbital metastasis
- 7.
Perineural spread of head and neck squamous cell carcinoma
- 1.
Referrals to consider.
- 1.
Ophthalmology
- 2.
Neurosurgery
- 3.
Potentially Radiation Oncology if the lesion is likely a meningioma or metastasis
- 1.
Diagnosis. Meningioma
Treatment considerations. An inflammatory etiology (IgG4-RD or idiopathic orbital inflammation—“pseudotumor”) is usually treated with steroid therapy. However, idiopathic orbital pseudotumor typically presents with orbital pain, and IgG4- RD typically presents with headache. Serum IgG4 can be elevated in patients with IgG4-RD but is nonspecific. In this case of painless orbital symptoms, biopsy/excision should be considered as orbital lymphoma can initially improve on steroid therapy and be difficult to detect on delayed biopsy after steroid treatment. Pathology can be determined with a targeted biopsy or at the time of surgical resection/debulking. The intracranial portion will likely be treated with adjuvant therapy due to difficulty with surgical resection of a lesion involving the cavernous sinus. Sarcoid can also involve the orbit. This possible diagnosis should be considered in the appropriate patient population. The presence of sclerosis and expansion of the adjacent sphenoid wing (hyperostosis) strongly favors a meningioma over the other entities in the differential for this case.
What happened in the case presented. Laboratory workup was negative for inflammatory markers. Given the progressive nature of her symptoms, surgical debulking of the intraorbital portion of the mass, followed by gamma knife therapy of the intracranial portion was recommended. The lesion was confirmed to be a meningioma (WHO grade I) at resection.
Teaching Points: Differentiating Skull-Based Meningioma From Orbital Inflammatory Lesion. The presence of adjacent sclerosis of the sphenoid bone (hyperostosis) is more suggestive of a meningioma rather than other orbital neoplasms such as lymphoma. Lack of orbital pain is also more consistent with a neoplasm rather than inflammation.
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