Evaluation of a ring enhancing lesion

Short answer

The lesion is probably in the left temporal lobe of the brain. The clinical picture suggests a primary central nervous system (CNS) tumor or brain abscess.

Discussion

Given that the physical examination found no relevant findings except for a right homonymous hemianopsia, it is reasonable to suspect a lesion in the left optic tract. The two week history of forgetfulness and headaches, although not specific, suggests that the lesion affects the temporal lobe of the brain and not the eye itself. The lesion is probably small because the patient has no symptoms of raised intracranial pressure (such as Cushing’s triad of hypertension, bradycardia, and bradypnea) and she is alert and oriented to person, location, and time. The symptoms suggest that the lesion is rapidly growing, but ischemic or hemorrhagic small vessel disease is unlikely because of the lack of acute onset findings. Both a primary CNS tumor and a brain abscess can lead to progressive loss of function within two weeks; however, the normal white cell count and C reactive protein concentration make a brain abscess less likely, although it cannot be excluded.

At this point an MRI is warranted. An emergency MRI is not needed because there are no symptoms of a high intracranial pressure lesion; however imaging should be scheduled within a few days because the symptoms have progressed over a short timeframe.

Short answer

Primary CNS tumor.

Discussion

Given the clinical picture and an MRI showing a single ring enhancing lesion with irregular borders (fig 1A⇓), the working diagnosis is that of a primary CNS tumor, followed by a brain abscess. It is important to understand the importance of the findings on MRI. Owing to breakdown in the blood-brain barrier, fluid has leaked into the lesion, giving a characteristic ring shaped appearance. Necrosis would be expected in the center of a primary CNS tumor, with no enhancement being seen inside the ring. A brain abscess would also not be expected to show enhancement inside the ring because of the large collection of pus. More radiological clues are therefore needed to narrow down the differential diagnosis.

Fig 1 Magnetic resonance imaging of the brain. (A) Axial T1 post-gadolinium image; (B) axial T2 post-gadolinium image; (C) axial diffusion weighted image

• Download figure
• Open in new tab
• Download powerpoint

High grade primary brain tumors tend to present radiologically as a mixed solid and cystic single lesion with an irregularly shaped border, similar to that seen here, whereas brain abscesses present as a more well formed ring devoid of solid components. The T2 weighted image (fig 1B) can be used to assess the degree of edema around the lesion. Tumors contain only a small to moderate amount of edema, as seen here, whereas abscesses tend to contain a greater amount of edema. Furthermore, the diffusion weighted image (fig 1C) highlights another important diagnostic clue: the signal intensity is relatively low, which suggests that the lesion is unlikely to be an abscess. CNS tumors contain watery, straw colored fluid which allows for relatively unrestricted diffusion and thus a low signal intensity; conversely, the thick collection of pus in an abscess impedes diffusion and allows for a high signal intensity.1 Thus, this lesion is probably neoplastic, although a tissue sample is needed to confirm the diagnosis.

The tumor could be a lymphoma, a metastasis, or primary in nature. Lymphomas classically present in the periventricular regions as uniformly enhancing solid lesions on MRI, making this is a less likely diagnosis. Brain metastases, although more common than primary CNS tumors, usually present as multiple lesions rather than single lesions, making metastasis a less likely diagnosis. The lesion is therefore likely to be a primary CNS tumor—specifically, a high grade glioblastoma because the necrotic center suggests poorly differentiated tissue that has outgrown its blood supply.

Short answer

Maximal safe resection or a biopsy if this is not possible.

Discussion

Because clinical and radiographic evidence suggests that the lesion is a malignant tumor, surgical resection or biopsy of the lesion is needed to obtain a diagnosis and improve prognosis. The initial management should include high dose corticosteroids to reduce the associated edema, which should also improve the symptoms. Steroids will probably cause leukocytosis, but this would not be suggestive of an abscess in the absence of other clinical or radiological findings. Surgery is used to obtain a diagnosis (through histological examination), reduce symptoms caused by the mass effect, prolong survival, and maintain or improve quality of life.2 Maximal safe resection is the mainstay of treatment of glioblastoma and, along with age, is an important prognostic factor.3 4 Depending on the proximity of the lesion to eloquent brain, the patient’s age, the degree of invasion, and the patient’s functionality, maximal resection of the lesion may not be possible and may even be detrimental; in these cases a biopsy may be the most appropriate option. An important prognostic factor is the Karnofsky performance scale score, which grades patients on the basis of functional impairment; patients with serious impairment (score <50) show benefit in terms of increased survival after resection.5

Patients with newly diagnosed and confirmed glioblastoma routinely receive both radiotherapy and temozolomide chemotherapy after maximal safe surgical resection in an attempt to improve quality of life and survival.6 Carmustine implants have also been used as a local chemotherapy option, but their high complication rate and marginal increase in survival mean that their benefit is doubtful.7 Overall survival remains less than 10% at five years,8 partly because of the aggressive nature of these tumors and their pervasiveness, which makes them difficult to fully resect. In elderly patients with multiple comorbidities it is therefore reasonable to discuss the option of using no treatment at all.

Short answer

A glial tumor showing features of atypia, endothelial proliferation, mitosis, and necrosis.

Discussion

Glioblastoma multiforme is also known as a grade IV astrocytoma and is one of the most common and lethal primary CNS tumors.9 It is definitively diagnosed with a tissue sample usually obtained during maximal safe resection. The World Health Organization grading scale classifies tumors according to the histological features of atypia, endothelial proliferation, mitosis, and necrosis. Grade IV tumors require at least three of the four features, with lower grade astrocytomas having fewer features and being less aggressive. A handful of tumor markers have also been shown to help predict the prognosis of these tumors. A mutation in the tumor marker isocitrate dehydrogenase 1 (IDH1) gene is seen in 12% of these tumors, and the presence of this mutation correlates with improved survival (median survival of 31 months in patients with mutated IDH1 v 14 months in patients with wild-type IDH1).9 10 Methylation of the O6-methylguanine DNA methyltransferase (MGMT) promoter, which occurs in 30-40% of glioblastomas, predicts the response to temozolomide therapy. Decreased expression of this gene secondary to promoter methylation has been suggested to allow temozolomide greater functionality as an alkylating agent—one study found that progression-free survival six months after temozolomide therapy was less than 7% in patients without MGMT methylation and 39.7% in patients with MGMT promoter methylation.11