|Year : 2018 | Volume
| Issue : 2 | Page : 163-166
Cystic brain lesions: Guess the mess
Anurag Gupta, Vanita Noronha, Kumar Prabhash, Amit Joshi, Vijay Patil, Abhishek Mahajan
Department of Medical Oncology and Radiodiagnosis, Tata Memorial Hospital, Mumbai, Maharashtra, India
|Date of Web Publication||17-May-2019|
Department of Medical Oncology and Radiodiagnosis, Tata Memorial Hospital, Dr. E. Borges Road, Parel, Mumbai - 400 012, Maharashtra
Source of Support: None, Conflict of Interest: None
A 67-year-old male patient, who is a known case of squamous cell carcinoma of esophagus received neoadjuvant chemotherapy (NACT). However, post 3 cycles of NACT, he had a fall. Computed tomography brain was performed which revealed a well-defined ring-enhancing lesion in the right cerebellar hemisphere. In the given clinical scenario, diagnosis of brain metastasis was made, and the patient received whole-brain radiation therapy. However, the patient deteriorated further and magnetic resonance imaging was performed. What is the diagnosis?
Keywords: Brain abscess, brain metastases, diffusion-weighted imaging, magnetic resonance, neoplasia
|How to cite this article:|
Gupta A, Noronha V, Prabhash K, Joshi A, Patil V, Mahajan A. Cystic brain lesions: Guess the mess. Cancer Res Stat Treat 2018;1:163-6
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given his/her consent for his/her images and other clinical information to be reported in the journal. The patient understands that his/her name and other identifying information will not be published and due efforts will be made to conceal his/her identity, but that anonymity cannot be guaranteed.
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Conflicts of interest
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| Introduction|| |
Cystic brain lesions/ring-enhancing lesions in the brain often pose a diagnostic dilemma due to multiple differentials and each have a varying line of management. In a known primary malignancy, brain metastasis is the most common cause and also a poor prognostic indicator as it significantly decreases life expectancy and changes the intent of therapy. The optimal management of cystic brain lesions requires a multidisciplinary approach tailored for each individual patient; therapeutic options include surgery or radiation in the form of whole-brain radiation therapy or stereotactic radiosurgery. However, it is crucial to rule out other causes of ring-enhancing lesions on imaging such as brain abscess, neurocysticercosis, tuberculoma, sarcoidosis, and a primary in the brain itself., Brain abscess is one of the important causes as it is a neurosurgical emergency. Different modalities of treatment are available including craniotomy, burr hole aspiration, stereotactic aspiration, and non-surgical options. Surgery is indicated to relieve intracranial mass effect and simultaneously provide or confirm the neuropathological diagnosis with low mortality and morbidity rates.
| Brain Abscess|| |
It is a collection of pus and necrotic inflammatory cells with microbes which are contained by the human immune system. It can be due to hematogenous spread (endocarditis, paradoxical embolus, pulmonary tuberculosis, etc.) or local spread (from sinuses, dental abscess, neurosurgery, etc.), especially in a person who is immunosuppressed. Brain abscess and metastases have a similar presentation presenting with severe headache, nausea, altered sensorium, focal neurological deficit, seizures, and signs of raised intracranial tension. Even laboratory markers such as erythrocyte sedimentation rate and white blood cell counts are often unreliable. To reach at early diagnosis of brain metastases is a crucial task for proper management.
Diagnostic workup includes computed tomography (CT) or magnetic resonance imaging (MRI). Brain CT imaging continues to have a role in brain abscess imaging, particularly as a screening examination for patients with acute neurologic deficits. Even non-enhanced CT can detect neurosurgical emergencies that require immediate intervention. However, CT is less sensitive as compared to MRI in detection and further characterization of ring-enhancing brain lesions.
Classical appearance of brain abscess on CT/MRI is of a well-marginated, rim-enhancing lesion with extensive edema [Figure 1]. However, metastases also have similar appearance on both CT as well as routine MRI sequences [Figure 2]. Here, diffusion-weighted imaging (DWI) comes to the rescue as it is useful in differentiating between an abscess and a necrotic neoplasm [Figure 3]. DWI is based on the principle of “ Brownian motion More Details” which states that water protons have a tendency to diffuse randomly in space. It is based upon Stejskal–Tanner sequence, which consists of a spin-echo sequence with diffusion gradients applied before and after 180° pulse. The magnitude of diffusion weighting is denoted by the “b value” or apparent diffusion coefficient (ADC). ADC value demonstrates cellularity and is inversely proportional to the amount of restricted diffusion. Pus in an abscess cavity is a viscous fluid of inflammatory cells, necrotic tissue, bacteria, and proteins. This viscous fluid grossly restricts the motion of water molecules, accounting for restricted diffusion in contrast with necrotic portion of a tumor. The ADC ratios for all pyogenic abscesses in a report varied from 0.45 to 0.8 and cystic necrotic tumor typically had higher values. Perfusion studies also play a role in differentiation as cystic metastases tend to show higher relative cerebral blood volume (rCBV) values than abscess. The rCBV ratio calculated (mean ± standard deviation) for high-grade gliomas, metastases, and abscess were 5.51 ± 2.08, 4.58 ± 2.19, and 0.76 ± 0.12, respectively. Hence, MRI with DWI, spectroscopy, and perfusion imaging should be used for evaluation of solitary brain lesion.
|Figure 1: Axial computed tomography brain plain (a) and contrast (b) showing hypodense necrotic lesion with peripheral rim enhancement and disproportionate edema|
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|Figure 2: Conventional axial magnetic resonance imaging sequences (a-c) represent T1, T2, T2 fluid-attenuated inversion-recovery sequences showing a T1 hypointense, T2 hyperintense lesion with hypointense rim. Fluid-attenuated inversion-recovery delineates disproportionate edema. (d and e) Represent gradient-recalled echo and susceptibility-weighted imaging which demonstrate no evidence of hemorrhage/calcification. (f) Centrally necrotic core with peripheral contrast rim enhancement with similar satellite lesion on postcontrast sequence|
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|Figure 3: (a and b) Intense restricted diffusion and low apparent diffusion coefficient values on diffusion-weighted images. (c) Lipid lactate peaks without rise in choline|
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Fluorodeoxyglucose-positron-emission tomography (FDG-PET) is a useful method for the study of glucose metabolism; however, due to overall high basal brain activity, it has low sensitivity. Hence, FDG-PET/CT is not an ideal investigation of choice in diagnosis of brain metastases. Abscesses with hemorrhage are a diagnostic challenge on conventional MRI as hemorrhagic component shows restriction on DWI and here, PET is helpful in differentiating abscess from other lesions.
| Differential Diagnosis of Ring-Enhancing Lesions|| |
Radiologically, ring-enhancing brain lesions have a variety of differential diagnoses that includes: cerebral abscess, tuberculoma, neurocysticercosis, metastasis, glioblastoma, subacute infarct/hemorrhage/contusion, demyelination (incomplete ring), tumefactive demyelinating lesion (incomplete ring), radiation necrosis, postoperative change, lymphoma – in an immunocompromised patient, leukemia, and thrombozed aneurysm. Salient differentiating features between brain abscess and metastases are described in [Figure 4].
|Figure 4: Key differences between cystic metastases and abscess. CT: computed tomography scans, DWI: diffusion weighted imaging, Perfusion: perfusion imaging, PET: Fluorodeoxyglucose-positron-emission tomography|
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Based on the following imaging characteristics, one can narrow down the differential diagnosis:
- Number of lesions – Multiple similar-sized rounded lesions at gray-white matter junction favors metastases or abscesses, irregular mass with adjacent secondary lesions embedded in the same region of 'edema' favors glioblastoma, and small (<1–2 cm) lesions with thin walls, especially if other calcific foci are present, suggest neurocysticercosis
- Enhancing wall – Thick and nodular is commonly seen in neoplasm, thin and regular in abscesses, incomplete ring often opened toward the cortex is a characteristic finding in demyelination, and T2 dark (hypointense)/intermediate signal capsule favors abscess (tuberculoma)
- Perilesional edema – Extensive edema relative to lesion size favors abscess and metastasis
- Typical primary brain tumors are usually more heterogeneous and show hyperperfusion and elevated choline and lactate levels with low-NAA levels and variable amount of restriction. However, in abscess, elevation of a succinate peak is relatively specific, but not present in all abscesses; high lactate, acetate, alanine, valine, leucine, and isoleucine levels peak may be present; choline/creatine and NAA peaks are reduced.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]