The Mammillary Bodies: A Review of Causes of Injury in Infants and Children

Impairments in the early consolidation of spatial memories via group II mGluR agonism in the mammillary bodies

mGluR2 receptors are widely expressed in limbic brain regions associated with memory, including the hippocampal formation, retrosplenial and frontal cortices, as well as subcortical regions including the mammillary bodies. mGluR2/3 agonists have been proposed as potential therapeutics for neurological and psychiatric disorders, however, there is still little known about the role of these receptors in cognitive processes, including memory consolidation. To address this, we assessed the effect of the mGluR2/3 agonist, eglumetad, on spatial memory consolidation in both mice and rats. Using the novel place preference paradigm, we found that post-sample injections of eglumetad impaired subsequent spatial discrimination when tested 6 h later. Using the immediate early gene c-fos as a marker of neural activity, we showed that eglumetad injections reduced activity in a network of limbic brain regions including the hippocampus and mammillary bodies. To determine whether the systemic effects could be replicated with more targeted manipulations, we performed post-sample infusions of the mGluR2/3 agonist 2R,4R-APDC into the mammillary bodies. This impaired novelty discrimination on a place preference task and an object-in-place task, again highlighting the role of mGluR2/3 transmission in memory consolidation and demonstrating the crucial involvement of the mammillary bodies in post-encoding processing of spatial information.

The Limbic System in Children and Adolescents With Attention-Deficit/Hyperactivity Disorder: A Longitudinal Structural Magnetic Resonance Imaging Analysis

Background

During childhood and adolescence, attention-deficit/hyperactivity disorder (ADHD) is associated with changes in symptoms and brain structures, but the link between brain structure and function remains unclear. The limbic system, often termed the "emotional network," plays an important role in a number of neurodevelopmental disorders, yet this brain network remains largely unexplored in ADHD. Investigating the developmental trajectories of key limbic system structures during childhood and adolescence will provide novel insights into the neurobiological underpinnings of ADHD.

Methods

Structural magnetic resonance imaging data (380 scans), emotional regulation (Affective Reactivity Index), and ADHD symptom severity (Conners 3 ADHD Index) were measured at up to 3 time points between 9 and 14 years of age in a sample of children and adolescents with ADHD (n = 57) and control children (n = 109).

Results

Compared with the control group, the ADHD group had lower volume of the amygdala (left: β standardized [β_std] = -0.38; right: β_std = -0.34), hippocampus (left: β_std = -0.44; right: β_std = -0.34), cingulate gyrus (left: β_std = -0.42; right: β_std = -0.32), and orbitofrontal cortex (right: β_std = -0.33) across development (9-14 years). There were no significant group-by-age interactions in any of the limbic system structures. Exploratory analysis found a significant Conners 3 ADHD Index-by-age interaction effect on the volume of the left mammillary body (β_std = 0.17) in the ADHD group across the 3 study time points.

Conclusions

Children and adolescents with ADHD displayed lower volume and atypical development in limbic system structures. Furthermore, atypical limbic system development was associated with increased symptom severity, highlighting a potential neurobiological correlate of ADHD severity.

Do the mammillary bodies atrophy with aging? A magnetic resonance imaging study

PURPOSE

This retrospective study aimed to explore age-related atrophy of the mammillary bodies (MBs) based on their temporal change using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

The study included 30 adult outpatients who presented to the hospital and were followed for more than 100 months with annual MRIs. The bi-ventricular width (BVW), third ventricle width (TVW), and bi-mammillary dimension (BMD) were measured on axial T2-weighted imaging and analyzed.

RESULTS

The 30 patients comprised 1 in their 40s, 5 in their 50s, 6 in their 60s, 11 in their 70s, 5 in their 80s, and 2 in their 90s. The MBs were consistently detected with left-to-right symmetry. The mean BVW was 32 ± 2.2 mm on the initial (BVW1) and 32 ± 2.4 mm on the last (BVW2) MRI. The mean TVW was 7.0 ± 2.3 mm on the initial (TVW1) and 7.6 ± 2.7 mm on the last (TVW2) MRI. Furthermore, the mean BMD was 9.9 ± 1.3 mm on the initial (BMD1) and 10 ± 1.3 mm on the last (BMD2) MRI. Statistically, no age ranges had a large dimension for BVW1, BVW2, TVW1, TVW2, BMD1, or BMD2. Changes between TVW1 and TVW2 were significantly different in the patients in their 80s; changes between BMD1 and BMD2 were not different for any age range or between sexes.

CONCLUSIONS

Aging alone does not seem to promote MB atrophy. In healthy brains, the MBs may be stationary structures throughout life.

Clinical characteristics and risk factors for bilateral lateral geniculate body pathology: a systematic review of the literature

BACKGROUND

Case presentation of acute onset bilateral painless vision loss caused by bilateral infarction of the lateral geniculate bodies (LGB) and a systematic review of the literature.

METHODS

A descriptive case report is presented on a 17-year-old female diagnosed with acute pancreatitis who developed acute onset bilateral painless vision loss. A systematic literature review of cases with bilateral LGB lesions was conducted across three electronic databases (PubMed/PubMed Central/MEDLINE, Scopus, and ScienceDirect). The review was conducted in concordance with PRISMA guidelines and prospectively registered on PROSPERO (CRD42022362491).

RESULTS

The reported 17-year-old female was found to have MRI findings consistent with bilateral hemorrhagic infarction of the LGB and Purtscher-like retinopathy. A systematic literature review of bilateral LGB infarction yielded 23 records for analysis. 19/23 (82.6%) of reported cases occurred in women. Bilateral vision loss was noted in all cases. The average reported age was 27 years old with a range from 2-50. Gastrointestinal pathology (e.g., pancreatitis, gastroenteritis) was present in 8/23 (34.7%) of cases. 8/23 (34.7%) cases had neuroimaging or pathological evidence of hemorrhagic transformation of the infarct. Most cases experienced partial recovery of visual loss; only one case (4.7%) had complete visual recovery. 9/23 (39.1%) cases were reported from the United States and 4/23 (17.3%) from India.

CONCLUSIONS

Bilateral LGB lesion is a rare cause of vision loss, typically caused by systemic diseases and with female preponderance. Purported pathophysiology relates to increased vulnerability of the LGB to ischemic and metabolic stress.

A 47-Year-Old Woman with Confusion and Weakness

A 47-Year-Old Woman with Confusion and WeaknessA 47-year-old woman with metastatic breast cancer presents with 3 months of confusion, memory loss, and lower-extremity weakness. How do you approach the evaluation, and what is the differential diagnosis?

A review of brain regions and associated post-concussion symptoms

The human brain is an exceptionally complex organ that is comprised of billions of neurons. Therefore, when a traumatic event such as a concussion occurs, somatic, cognitive, behavioral, and sleep impairments are the common outcome. Each concussion is unique in the sense that the magnitude of biomechanical forces and the direction, rotation, and source of those forces are different for each concussive event. This helps to explain the unpredictable nature of post-concussion symptoms that can arise and resolve. The purpose of this narrative review is to connect the anatomical location, healthy function, and associated post-concussion symptoms of some major cerebral gray and white matter brain regions and the cerebellum. As a non-exhaustive description of post-concussion symptoms nor comprehensive inclusion of all brain regions, we have aimed to amalgamate the research performed for specific brain regions into a single article to clarify and enhance clinical and research concussion assessment. The current status of concussion diagnosis is highly subjective and primarily based on self-report of symptoms, so this review may be able to provide a connection between brain anatomy and the clinical presentation of concussions to enhance medical imaging assessments. By explaining anatomical relevance in terms of clinical concussion symptom presentation, an increased understanding of concussions may also be achieved to improve concussion recognition and diagnosis.

Reduced mammillary body volume in individuals with a schizophrenia diagnosis: an analysis of the COBRE data set

While the frontal cortices and medial temporal lobe are well associated with schizophrenia, the involvement of wider limbic areas is less clear. The mammillary bodies are important for both complex memory formation and anxiety and are implicated in several neurological disorders that present with memory impairments. However, little is known about their role in schizophrenia. Post-mortem studies have reported a loss of neurons in the mammillary bodies but there are also reports of increased mammillary body volume. The findings from in vivo MRI studies have also been mixed, but studies have typically only involved small sample sizes. To address this, we acquired mammillary body volumes from the open-source COBRE dataset, where we were able to manually measure the mammillary bodies in 72 individuals with a schizophrenia diagnosis and 74 controls. Participant age ranged from 18 to 65. We found the mammillary bodies to be smaller in the patient group, across both hemispheres, after accounting for the effects of total brain volume and gender. Hippocampal volumes, but not subiculum or total grey matter volumes, were also significantly lower in patients. Given the importance of the mammillary bodies for both memory and anxiety, this atrophy could contribute to the symptomology in schizophrenia.

Mammillary body and hypothalamic volumes in mood disorders

We have previously reported an in vivo enlargement of the left hypothalamus in mood disorders using 7 T magnetic resonance imaging. The aim of this follow-up study was to find out whether the hypothalamic volume difference may be located in the mammillary bodies (MB) rather than being widespread across the hypothalamus. We developed and evaluated a detailed segmentation algorithm that allowed a reliable segmentation of the MBs, and applied it to 20 unmedicated (MDDu) and 20 medicated patients with major depressive disorder, 21 medicated patients with bipolar disorder, and 23 controls. 20 out of 23 healthy controls were matched to the MDDu. We tested for group differences in MB and hypothalamus without MB (HTh) volumes using analyses of covariance. Associations between both volumes of interest were analysed using bivariate and partial correlations. In contrast to postmortem findings, we found no statistically significant differences of the MB volumes between the study groups. Left HTh volumes differed significantly across the study groups after correction for intracranial volume (ICV) and for ICV and sex. Our result of an HTh enlargement in mood disorders was confirmed by a paired t-test between the matched pairs of MDDu and healthy controls using the native MB and HTh volumes. In the whole sample, MB volumes correlated significantly with the ipsilateral HTh volumes. Our results indicate a structural relationship between both volumes, and that our previous in vivo finding of a hypothalamus enlargement does not extend to the MB, but is limited to the HTh. The enlargement is more likely related to the dysregulation of the HPA axis than to cognitive dysfunctions accompanying mood disorders.

Delineation of intermammillary relationships using magnetic resonance imaging

PURPOSE

No study has investigated intermammillary relationships using neuroimaging modalities. This study aimed to explore them using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

We enrolled 72 patients who underwent conventional MRI examinations, followed by constructive interference steady-state sequence in the coronal plane. The intermammillary distances (IMDs) were measured at the uppermost level of the intermammillary gap (IMD_upp) and the lowest level (IMD_low) of the mammillary bodies (MBs).

RESULTS

MBs with varying morphologies were consistently delineated. The appearance of both MBs could be classified into four patterns based on the size and relative levels, with the symmetrical type being the most common. Intermammillary relationships exhibited five patterns. In 69%, the IMD_upp was discernible and measured 0.7 ± 0.4 mm, while it was not discernible in 31% due to the presence of intermammillary connection and adhesion. The age distribution did not differ between populations with and without discernible IMD_upp. The IMD_low was measured 4.4 ± 0.9 mm. Although the IMD_low was not significantly different between both sexes; it was longer in subjects in their 70s.

CONCLUSIONS

Intermammillary relationships show variable morphologies with gaps formed between both MBs. The IMD_low may become more evident in association with age-related increase in the width of the third ventricle and atrophy of the MBs.

Normative mammillary body volumes: From the neonatal period to young adult

The mammillary bodies may be small, but they have an important role in encoding complex memories. Mammillary body pathology often occurs following thiamine deficiency but there is increasing evidence that the mammillary bodies are also compromised in other neurological conditions and in younger ages groups. For example, the mammillary bodies are frequently affected in neonates with hypoxic-ischemic encephalopathy. At present, there is no normative data for the mammillary bodies in younger groups making it difficult to identify abnormalities in neurological disorders. To address this, the present study set out to develop a normative dataset for neonates and for children to young adult. A further aim was to determine whether there were laterality or sex differences in mammillary body volumes. Mammillary body volumes were obtained from MRI scans from 506 participants across two datasets. Measures for neonates were acquired from the Developing Human Connectome Project database (156 male; 100 female); volumes for individuals aged 6-24 were acquired from the NICHE database (166 males; 84 females). Volume measurements were acquired using a semi-automated multi-atlas segmentation approach. Mammillary body volumes increased up to approximately 15 years-of-age. The left mammillary body was marginally, but significantly, larger than the right in the neonates with a similar pattern in older children/young adults. In neonates, the mammillary bodies in males were slightly bigger than females but no sex differences were present in older children/young adults. Given the increasing presentation of mammillary body pathology in neonates and children, these normative data will enable better assessment of the mammillary bodies in healthy and at-risk populations.