PMC9805647_01
Axial (left), coronal (middle), and sagittal (right) CT scans on admission showing an area of low attenuation with a central hyperattenuating focus in the left frontal lobe causing mass effect on the frontal horn of the left lateral ventricle and rightward 2 mm midline shift.
SNI-13-591-g001.jpg
PMC9805647_01_SNI-13-591-g001.jpg
F1
A head CT demonstrated a hyperattenuating focus in the left insular region surrounded by an area of low attenuation, suggestive of vasogenic edema [Figure 1].
Serial brain magnetic resonance imaging (MRI) scans performed throughout the patient's hospital course: (a) on admission to MGH showing left insular mass with irregularly marginated peripheral enhancement with central necrotic and hemorrhagic foci causing mass effect and a 2 mm midline shift to the right. Fluid-attenuated inversion recovery (FLAIR) imaging demonstrates surrounding edema and diffusion-weighted imaging (DWI) demonstrates restricted diffusion in the center of the lesion. (b) Following acute clinical decline before first surgery revealed an interval increase in the left insular lesion with more well-defined peripheral enhancement. Mass effect has progressed causing increased rightward midline shift. FLAIR imaging shows increased peripheral edema. (c) Postoperative demonstrating a mildly decreased size in the lesion. There is a loculated rim-enhancing component along the superolateral margin of the resection cavity and a focus of apparent discontinuous rim enhancement along the inferolateral posterior aspect of this loculation. (d) Surveillance MRI on post operative day 7 shows an expansion of the previously partially collapsed appearance of the abscess cavity walls. Extensive FLAIR hyperintensity with mass effect surrounding the abscess cavity has increased causing increased extracranial herniation and left to right midline shift. The images show T1 postcontrast axial (labeled as 1), sagittal (labeled as 2), and coronal (labeled as 3); axial FLAIR (labeled as 4); and axial DWI (labeled as 5).
SNI-13-591-g002.jpg
PMC9805647_01_SNI-13-591-g002.jpg
F2
T1 hypointensity, heterogeneous T2 hyperintensity, and irregular peripheral enhancement [Figure 2a]. The treatment team felt that the radiographic images were most consistent with a malignant etiology. Her cerebral edema had also significantly worsened, causing a 2 mm midline shift to the right and mass effect on the left lateral ventricle and basal ganglia [Figure 2b]. A loculated rim-enhancing component along the superolateral margin of the dominant abscess cavity seen on postoperative MRI was suspicious for residual abscess [Figure 2c]. After 1 week of antibiotics, a surveillance brain MRI on POD 7 showed a likely recurrence of the abscess with rightward midline shift progression, worsening parenchymal herniation through the craniectomy defect, and subfalcine and uncal herniation [Figure 2d].
Hematoxylin and eosin-stained images show abscess with capsule (a), regions of necrosis (b), regions with early capsule formation (c), and granulation tissue with neutrophilic infiltrate (d). Scale bars denote 500 um (a), 200 um (b and c), and 100 um (d).
SNI-13-591-g003.jpg
PMC9805647_01_SNI-13-591-g003.jpg
F3
Histologic examination showed portions of brain with abundant necrosis and a dense neutrophilic infiltrate, consistent with abscess and excluding a superimposed underlying malignancy [Figures 3a and b]. Surrounding the necrotic regions were areas of granulation tissue and granulation-type tissue indicative of early formation of a capsule [Figures 3c and d].
(a) Postsurgical changes from left-sided craniectomy with extensive edema of brain parenchyma causing herniation of the left cerebral hemisphere through the craniectomy defect, minimal rightward midline shift, and effacement of the left lateral ventricle. (b) A follow-up scan 2 months after discharge shows improving cerebral edema and no abnormal enhancement to suggest persistent or recurrent abscess. T1 postcontrast axial, sagittal, and coronal (c), axial fluid-attenuated inversion recovery (d), and axial diffusion-weighted imaging (e) sequences from her most recent follow-up MRI taken 3 months after discharge shows substantially decreased brain herniation and swelling of the left cerebral hemisphere with residual enhancement within the insula and mild residual FLAIR hyperintensity involving the left frontal lobe, insula, and left temporal lobe.
SNI-13-591-g004.jpg
PMC9805647_01_SNI-13-591-g004.jpg
F4
One week after surgery, head CT revealed a re-expansion of the previously collapsed abscess cavity, significant edema with mass effect, and a subcutaneous hematoma [Figure 4a]. A 2-month follow-up head CT demonstrated improving cerebral edema and no evidence of a persistent or recurrent abscess [Figure 4b]. Her most recent follow-up MRI showed substantially decreased brain herniation and edema [Figures 4c-e].