Ectopic cerebellar tissue of the posterior cranial fossa: diffusion tensor tractography and MR spectroscopy findings

Methodological considerations on diffusion MRI tractography in infants aged 0-2 years: a scoping review

Diffusion MRI (dMRI) enables studying the complex architectural organization of the brain's white matter (WM) through virtual reconstruction of WM fiber tracts (tractography). Despite the anticipated clinical importance of applying tractography to study structural connectivity and tract development during the critical period of rapid infant brain maturation, detailed descriptions on how to approach tractography in young infants are limited. Over the past two decades, tractography from infant dMRI has mainly been applied in research settings and focused on diffusion tensor imaging (DTI). Only few studies used techniques superior to DTI in terms of disentangling information on the brain's organizational complexity, including crossing fibers. While more advanced techniques may enhance our understanding of the intricate processes of normal and abnormal brain development and extensive knowledge has been gained from application on adult scans, their applicability in infants has remained underexplored. This may partially be due to the higher technical requirements versus the need to limit scan time in young infants. We review various previously described methodological practices for tractography in the infant brain (0-2 years-of-age) and provide recommendations to optimize advanced tractography approaches to enable more accurate reconstructions of the brain WM's complexity. IMPACT: Diffusion tensor imaging is the technique most frequently used for fiber tracking in the developing infant brain but is limited in capability to disentangle the complex white matter organization. Advanced tractography techniques allow for reconstruction of crossing fiber bundles to better reflect the brain's complex organization. Yet, they pose practical and technical challenges in the fast developing young infant's brain. Methods on how to approach advanced tractography in the young infant's brain have hardly been described. Based on a literature review, recommendations are provided to optimize tractography for the developing infant brain, aiming to advance early diagnosis and neuroprotective strategies.

Neuroimaging Features of Ectopic Cerebellar Tissue: A Case Series Study of a Rare Entity

Ectopic cerebellar tissue is a rare entity likely secondary to multiple, interacting, developmental errors during embryogenesis. Multiple sites of ectopic cerebellar tissue have been reported, including extracranial locations; however, an intracranial location is most common. We report on the MR imaging findings of a multi-institutional series of 7 ectopic cerebellar tissue cases (2 males, 4 females, 1 fetal) ranging from 22 weeks 5 days' gestational age to 18 years of age. All cases of ectopic cerebellar tissue were diagnosed incidentally, while imaging was performed for other causes. Ectopic cerebellar tissue was infratentorial in 6/7 patients and supratentorial in 1/7 patients. All infratentorial ectopic cerebellar tissue was connected with the brain stem or cerebellum. MR imaging signal intensity was identical to the cerebellar gray and white matter signal intensity on all MR imaging sequences in all cases. Ectopic cerebellar tissue should be considered in the differential diagnoses of extra-axial masses with signal characteristics similar to those of the cerebellum. Surgical biopsy or resection is rarely necessary, and in most cases, MR imaging is diagnostic.

Developmentally anomalous cerebellar encephalocele arising within the cerebellopontine angle and extending into the adjacent skull base in a pediatric patient

Lesions of the cerebellopontine angle (CPA) in young children are rare, with the most common being arachnoid cysts and epidermoid inclusion cysts. The authors report a case of an encephalocele containing heterotopic cerebellar tissue arising from the right middle cerebellar peduncle and filling the right internal acoustic canal in a 2-year-old female patient. Her initial presentation included a focal left 6th nerve palsy. Magnetic resonance imaging was suggestive of a high-grade tumor of the right CPA. The lesion was removed via a retrosigmoid approach, and histopathologic analysis revealed heterotopic atrophic cerebellar tissue. This report is the first description of a heterotopic cerebellar encephalocele within the CPA and temporal skull base of a pediatric patient.

Ectopic Cerebellar Tissue in the Occipital Bone: A Case Report

Ectopic cerebellar tissue has only been described in isolated case reports, with only two reported cases in adult patients. We report the case of a 63-year-old woman with progressive, medically refractory headaches. A scan showed an intraosseous lesion of the midline occipital bone. Surgical resection of the soft tissue lesion was undertaken. Her headaches ceased postoperatively. Histopathological analysis revealed cerebellar cortical tissue with a surrounding meningothelial cell layer, characteristic of cerebellar ectopia. This is the second reported case of an intraosseous location of this lesion, and only the third case described in an adult patient. Our findings illustrate a rare cause of headaches and support the therapeutic roles of surgical treatment for this extremely rare condition.

Intraventricular Ectopic Cerebellum

BACKGROUND

Cerebellar ectopy is a rare finding, with few cases previously reported. Intraventricular localized cerebellar ectopy was described in only 1 case within the fourth ventricle.

CASE DESCRIPTION

A 9-year-old girl suffered for 2 years from bilateral frontoparietal headaches, sometimes accompanied by vomiting and photophobia. Magnetic resonance imaging demonstrated an oval-shaped lesion within the left lateral ventricle, characterized by well-defined margins without a clear cleavage plane from the adjacent choroid plexus. The mass presented an intermediate signal on T1- and T2-weighted sequences, similar to gray matter, and reduced ADC values on ADC maps compared with white matter, with no enhancement after gadolinium-based contrast injection. After resection, macroscopic examination revealed an organoid structure with leptomeningeal lining and a clear-cut cortex and white matter components. Histology demonstrated normal cerebellum with a double-layered cortex and normal underlying white matter. The cerebellar ectopy was focally covered by bundles of capillary vascular structures covered by a monostratified ependymal cell lining, consistent with choroid plexus.

CONCLUSIONS

We describe, for the first time to our knowledge, the case of a child with ectopic cerebellar tissue harboring the supratentorial ventricular system. Plausible etiologic mechanism consists in the herniation of the cerebellar germinal tissue into the ventricular system through the ependyma, allowing cell migration to the supratentorial compartment, followed by maturation into the normal cerebellum.

Ectopic cerebellar tissue in the occipital bone: a case report

BACKGROUND

Ectopic cerebellar tissue located distantly from the normal cerebellum is very rare, and its pathophysiology remains to be elucidated.

CASE PRESENTATION

We report an extremely rare case of intraosseous ectopic cerebellum detected incidentally at suboccipital craniotomy in a 46-year-old Japanese woman with hemifacial spasm. She had a small bone defect in the occipital bone, which contained a tiny area of soft tissue surrounded by cerebrospinal fluid connecting to the normal subarachnoid space through a dural opening. Histopathology demonstrated cerebellar cortex tissue consisting of molecular and granular cell layers.

CONCLUSIONS

This is the first report of glioneuronal ectopia within the skull bone separated from normal brain tissue, and it is important to distinguish this entity from other osteolytic lesions.