What is microbial dormancy?

Life can be stressful. One way to deal with stress is to simply wait it out. Microbes do this by entering a state of reduced activity and increased resistance commonly called 'dormancy'. But what is dormancy? Different scientific disciplines emphasize distinct traits and phenotypic ranges in defining dormancy for their microbial species and system-specific questions of interest. Here, we propose a unified definition of microbial dormancy, using a broad framework to place earlier discipline-specific definitions in a new context. We then discuss how this new definition and framework may improve our ability to investigate dormancy using multi-omics tools. Finally, we leverage our framework to discuss the diversity of genomic mechanisms for dormancy in an extreme environment that challenges easy definitions - the permafrost.

Building a queer- and trans-inclusive microbiology conference

Microbiology conferences can be powerful places to build collaborations and exchange ideas, but for queer and transgender (trans) scientists, they can also become sources of alienation and isolation. Many conference organizers would like to create welcoming and inclusive events but feel ill-equipped to make this vision a reality, and a historical lack of representation of queer and trans folks in microbiology means we rarely occupy these key leadership roles ourselves. Looking more broadly, queer and trans scientists are systematically marginalized across scientific fields, leading to disparities in career outcomes, professional networks, and opportunities, as well as the loss of unique scientific perspectives at all levels. For queer and trans folks with multiple, intersecting, marginalized identities, these barriers often become even more severe. Here, we draw from our experiences as early-career microbiologists to provide concrete, practical advice to help conference organizers across research communities design inclusive, safe, and welcoming conferences, where queer and trans scientists can flourish.

Symbiotic UCYN-A strains co-occurred with El Niño, relaxed upwelling, and varied eukaryotes over 10 years off Southern California

Biological nitrogen fixation, the conversion of N2 gas into a bioavailable form, is vital to sustaining marine primary production. Studies have shifted beyond traditionally studied tropical diazotrophs. Candidatus Atelocyanobacterium thalassa (or UCYN-A) has emerged as a focal point due to its streamlined metabolism, intimate partnership with a haptophyte host, and broad distribution. Here, we explore the environmental parameters that govern UCYN-A's presence at the San Pedro Ocean Time-series (SPOT), its host specificity, and statistically significant interactions with non-host eukaryotes from 2008-2018. 16S and 18S rRNA gene sequences were amplified by "universal primers" from monthly samples and resolved into Amplicon Sequence Variants, allowing us to observe multiple UCYN-A symbioses. UCYN-A1 relative abundances increased following the 2015-2016 El Niño event. This "open ocean ecotype" was present when coastal upwelling declined, and Ekman transport brought tropical waters into the region. Network analyses reveal all strains of UCYN-A co-occur with dinoflagellates including Lepidodinium, a potential predator, and parasitic Syndiniales. UCYN-A2 appeared to pair with multiple hosts and was not tightly coupled to its predominant host, while UCYN-A1 maintained a strong host-symbiont relationship. These biological relationships are particularly important to study in the context of climate change, which will alter UCYN-A distribution at regional and global scales.

Size-fractionated microbiome observed during an eight-month long sampling in Jiaozhou Bay and the Yellow Sea

Jiaozhou Bay is a typical semi-enclosed bay with a temperate climate imposed by strong anthropogenic influence. To investigate microbial biodiversity and ecosystem services in this highly dynamic coastal environment, we conducted a monthly microbial survey spanning eight months at two stations in the bay and the open Yellow Sea starting in April 2015. This report provides a comprehensive inventory of amplicon sequences and environmental microbial genomes from this survey. In total, 2,543 amplicon sequence variants were obtained with monthly relative abundance profiles in three size fractions (>2.7 μm, 2.7-0.7 μm, and 0.7-0.22 μm). Shotgun metagenomes yielded 915 high-quality metagenome-assembled genomes with ≥50% completeness and ≤5% contamination. These environmental genomes comprise 27 bacterial and 5 archaeal phyla. We expect this comprehensive dataset will facilitate a better understanding of coastal microbial ecology.

NetGAM: Using generalized additive models to improve the predictive power of ecological network analyses constructed using time-series data

Ecological network analyses are used to identify potential biotic interactions between microorganisms from species abundance data. These analyses are often carried out using time-series data; however, time-series networks have unique statistical challenges. Time-dependent species abundance data can lead to species co-occurrence patterns that are not a result of direct, biotic associations and may therefore result in inaccurate network predictions. Here, we describe a generalize additive model (GAM)-based data transformation that removes time-series signals from species abundance data prior to running network analyses. Validation of the transformation was carried out by generating mock, time-series datasets, with an underlying covariance structure, running network analyses on these datasets with and without our GAM transformation, and comparing the network outputs to the known covariance structure of the simulated data. The results revealed that seasonal abundance patterns substantially decreased the accuracy of the inferred networks. In addition, the GAM transformation increased the predictive power (F1 score) of inferred ecological networks on average and improved the ability of network inference methods to capture important features of network structure. This study underscores the importance of considering temporal features when carrying out network analyses and describes a simple, effective tool that can be used to improve results.

Exploring the functional composition of the human microbiome using a hand-curated microbial trait database

BACKGROUND

Even when microbial communities vary wildly in their taxonomic composition, their functional composition is often surprisingly stable. This suggests that a functional perspective could provide much deeper insight into the principles governing microbiome assembly. Much work to date analyzing the functional composition of microbial communities, however, relies heavily on inference from genomic features. Unfortunately, output from these methods can be hard to interpret and often suffers from relatively high error rates.

RESULTS

We built and analyzed a domain-specific microbial trait database from known microbe-trait pairs recorded in the literature to better understand the functional composition of the human microbiome. Using a combination of phylogentically conscious machine learning tools and a network science approach, we were able to link particular traits to areas of the human body, discover traits that determine the range of body areas a microbe can inhabit, and uncover drivers of metabolic breadth.

CONCLUSIONS

Domain-specific trait databases are an effective compromise between noisy methods to infer complex traits from genomic data and exhaustive, expensive attempts at database curation from the literature that do not focus on any one subset of taxa. They provide an accurate account of microbial traits and, by limiting the number of taxa considered, are feasible to build within a reasonable time-frame. We present a database specific for the human microbiome, in the hopes that this will prove useful for research into the functional composition of human-associated microbial communities.

NCBI's Virus Discovery Codeathon: Building "FIVE" -The Federated Index of Viral Experiments API Index

Viruses represent important test cases for data federation due to their genome size and the rapid increase in sequence data in publicly available databases. However, some consequences of previously decentralized (unfederated) data are lack of consensus or comparisons between feature annotations. Unifying or displaying alternative annotations should be a priority both for communities with robust entry representation and for nascent communities with burgeoning data sources. To this end, during this three-day continuation of the Virus Hunting Toolkit codeathon series (VHT-2), a new integrated and federated viral index was elaborated. This Federated Index of Viral Experiments (FIVE) integrates pre-existing and novel functional and taxonomy annotations and virus–host pairings. Variability in the context of viral genomic diversity is often overlooked in virus databases. As a proof-of-concept, FIVE was the first attempt to include viral genome variation for HIV, the most well-studied human pathogen, through viral genome diversity graphs. As per the publication of this manuscript, FIVE is the first implementation of a virus-specific federated index of such scope. FIVE is coded in BigQuery for optimal access of large quantities of data and is publicly accessible. Many projects of database or index federation fail to provide easier alternatives to access or query information. To this end, a Python API query system was developed to enhance the accessibility of FIVE.

Linking high GC content to the repair of double strand breaks in prokaryotic genomes

Genomic GC content varies widely among microbes for reasons unknown. While mutation bias partially explains this variation, prokaryotes near-universally have a higher GC content than predicted solely by this bias. Debate surrounds the relative importance of the remaining explanations of selection versus biased gene conversion favoring GC alleles. Some environments (e.g. soils) are associated with a high genomic GC content of their inhabitants, which implies that either high GC content is a selective adaptation to particular habitats, or that certain habitats favor increased rates of gene conversion. Here, we report a novel association between the presence of the non-homologous end joining DNA double-strand break repair pathway and GC content; this observation suggests that DNA damage may be a fundamental driver of GC content, leading in part to the many environmental patterns observed to-date. We discuss potential mechanisms accounting for the observed association, and provide preliminary evidence that sites experiencing higher rates of double-strand breaks are under selection for increased GC content relative to the genomic background.

The overall nucleotide composition of an organism’s genome varies greatly between species. Previous work has identified certain environmental factors (e.g., oxygen availability) associated with the relative number of GC bases as opposed to AT bases in the genomes of species. Many of these environments that are associated with high GC content are also associated with relatively high rates of DNA damage. We show that organisms possessing the non-homologous end-joining DNA repair pathway, which is one mechanism to repair DNA double-strand breaks, have an elevated GC content relative to expectation. We also show that certain sites on the genome that are particularly susceptible to double strand breaks have an elevated GC content. This leads us to suggest that an important underlying driver of variability in nucleotide composition across environments is the rate of DNA damage (specifically double-strand breaks) to which an organism living in each environment is exposed.

Trait-based analysis of the human skin microbiome

BACKGROUND

The past decade of microbiome research has concentrated on cataloging the diversity of taxa in different environments. The next decade is poised to focus on microbial traits and function. Most existing methods for doing this perform pathway analysis using reference databases. This has both benefits and drawbacks. Function can go undetected if reference databases are coarse-grained or incomplete. Likewise, detection of a pathway does not guarantee expression of the associated function. Finally, function cannot be connected to specific microbial constituents, making it difficult to ascertain the types of organisms exhibiting particular traits-something that is important for understanding microbial success in specific environments. A complementary approach to pathway analysis is to use the wealth of microbial trait information collected over years of lab-based, culture experiments.

METHODS

Here, we use journal articles and Bergey's Manual of Systematic Bacteriology to develop a trait-based database for 971 human skin bacterial taxa. We then use this database to examine functional traits that are over/underrepresented among skin taxa. Specifically, we focus on three trait classes-binary, categorical, and quantitative-and compare trait values among skin taxa and microbial taxa more broadly. We compare binary traits using a Chi-square test, categorical traits using randomization trials, and quantitative traits using a nonparametric relative effects test based on global rankings using Tukey contrasts.

RESULTS

We find a number of traits that are over/underrepresented within the human skin microbiome. For example, spore formation, acid phosphatase, alkaline phosphatase, pigment production, catalase, and oxidase are all less common among skin taxa. As well, skin bacteria are less likely to be aerobic, favoring, instead, a facultative strategy. They are also less likely to exhibit gliding motility, less likely to be spirillum or rod-shaped, and less likely to grow in chains. Finally, skin bacteria have more difficulty at high pH, prefer warmer temperatures, and are much less resilient to hypotonic conditions.

CONCLUSIONS

Our analysis shows how an approach that relies on information from culture experiments can both support findings from pathway analysis, and also generate new insights into the structuring principles of microbial communities.

Imaging findings of bisphosphonate-associated osteonecrosis of the jaws

BACKGROUND AND PURPOSE

Bisphosphonates are drugs that decrease bone turnover by inhibiting osteoclast activity. An association between the use of bisphosphonates and osteonecrosis of the maxilla and mandible has recently been described. This study describes the imaging findings of bisphosphonate-associated osteonecrosis of the jaws.

MATERIALS AND METHODS

This is a retrospective series of 15 clinically diagnosed patients, identified at 3 centers. Eleven patients were women, of whom 6 had breast cancer, 3 had osteoporosis, and 2 had multiple myeloma. Of the 4 male patients, 2 had prostate cancer, 1 had multiple myeloma, and 1 had osteoporosis. The age range of the patients was 52-85 years (average, 68 years). The mandible was the clinical site of involvement in 11 patients, and the maxilla was involved in 4 patients. Imaging consisted of orthopantomograms in 14 patients, CT scans in 5 patients, and radionuclide bone scan in 1 patient. Nine patients had sequential imaging. Two radiologists reviewed the images.

RESULTS

All of the patients had a degree of osseous sclerosis, most commonly involving the alveolar margin, but lamina dura thickening and full-thickness sclerosis were also observed. The sclerotic change encroached on the mandibular canal in 3 patients. Less commonly encountered findings included poorly healing or nonhealing extraction sockets, periapical lucencies, widening of the periodontal ligament space, osteolysis, sequestra, oroantral fistula, soft tissue thickening, and periosteal new bone formation.

CONCLUSIONS

The most common finding in bisphosphonate-associated osteonecrosis was osseous sclerosis. This varied from subtle thickening of the lamina dura and alveolar crest to attenuated osteopetrosis-like sclerosis.

MRI detection of cervical metastasis from differentiated thyroid carcinoma

BACKGROUND

With the advent of the use of serum thyroglobulin as a marker for the recurrence of well-differentiated thyroid cancer (WDTC) after total thyroidectomy, clinicians are increasingly faced with the diagnostic dilemma of detecting the site of recurrence in thyroglobulin-positive patients with normal clinical examinations. The high protein content of this thyroglobulin may make it specifically detectable by magnetic resonance (MR) imaging.

OBJECTIVE

To determine the ability of MR imaging to detect the presence of metastatic WDTC in cervical lymph nodes.

STUDY DESIGN

Retrospective cohort.

METHODS

Blinded review by two independent head and neck radiologists of 34 head and neck MR scans obtained from 26 patients with thyroid cancer (12 with primary disease and 14 with recurrent disease) all of whom subsequently underwent surgical removal of the lymph nodes considered at risk by imaging.

RESULTS

The average overall percent sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of MR imaging were 95%, 51%, 84%, 78%, and 83%, respectively. The concordance between the two radiologists was 69%. There was no overall difference in the ability of the MR scan to detect the presence of disease in the upper jugular, lower jugular, or paratracheal nodal stations. However, it was more useful for papillary carcinoma (PPV 86%, accuracy 85%) than for follicular carcinoma or the follicular variant of papillary carcinoma (PPV 63%, accuracy 67%).

CONCLUSION

MR imaging is a sensitive and accurate technique for the detection of WDTC, particularly papillary carcinoma, metastatic to cervical lymph nodes. However, the lower specificity of this modality precludes its use as a screening tool.

"Puffed-cheek" CT improves evaluation of the oral cavity

BACKGROUND AND PURPOSE

Maneuvers that distend a lumen facilitate radiographic examinations. In evaluation of the upper aerodigestive tract, Valsalva and phonation maneuvers complement barium fluoroscopy. The current work investigates "puffed-cheek" CT to improve visualization of oral cavity tumors.

METHODS

Seven patients (ages 17 to 86 years) underwent conventional and puffed-cheek CT. Five had squamous cell carcinoma, one had benign verrucous hyperplasia of the buccal mucosa, one had "cheek swelling," and one had a pulsatile cheek mass. Conventional contrast-enhanced axial CT scans (3-mm thick, no interslice gap) were obtained through the oral cavity and neck. Each patient then pursed the lips and puffed out the cheeks, and axial images were obtained through the oral cavity (puffed-cheek scans).

RESULTS

Three patients had normal conventional CT scans whereas puffed-cheek scans clearly showed the mass. Conventional CT in three patients showed a mass inseparable from two mucosal surfaces whereas puffed-cheek images clearly showed which surface the tumor involved. Two patients had normal conventional and puffed-cheek CT studies; in one, the physical examination was also normal. The other patient was a teenager with orthodontic appliances that created artifacts on both conventional and puffed-cheek images. Conventional angiography in this patient revealed a facial artery aneurysm.

CONCLUSION

The puffed-cheek CT maneuver is easily taught, and patients comply readily. Puffed-cheek CT scans provide a clearer and more detailed evaluation of mucosal surfaces of the oral cavity than do conventional scans. In selected patients, the puffed-cheek technique can supplement conventional CT studies.

Hydroxyapatite: an alternative method of frontal sinus obliteration

Obliteration of the frontal sinus may be necessary for the treatment of chronic sinusitis, infectious complications, trauma, and benign and malignant neoplasms. Hydroxyapatite cement (HAC) is a relatively new material that is approved for the repair of cranial defects. HAC has been successfully used to obliterate the frontal sinus in 19 patients with few minor complications and the avoidance of donor site morbidity. Compared with other alloplastic materials, HAC has the advantages of easy use, biocompatibility, and osseointegration.

Traumatic neuroma after neck dissection: CT characteristics in four cases

BACKGROUND AND PURPOSE

Traumatic neuroma, an attempt by an injured nerve to regenerate, may present as a palpable nodule or an area sensitive to touch (trigger point) after neck dissection. The purpose of this study was to identify CT characteristics of traumatic neuroma in four patients after neck dissection.

METHODS

Between April 1995 and November 1998, the CT studies in three men and one woman (ages, 45-64 years) who had had a radical neck dissection and a nodule posterior to the carotid artery were reviewed retrospectively. CT was performed 1.5 to 6 years after neck dissection with clinical correlation and/or pathologic examination. Three patients had squamous cell carcinoma of the upper aerodigestive tract and one had a primary parotid adenocarcinoma.

RESULTS

Three patients with a traumatic neuroma had a centrally radiolucent nodule with peripherally dense rim and intact layer of overlying fat, which was stable on CT studies for 1 to 2 years. One of these had a clinical trigger point. The fourth patient with a pathologically proved traumatic neuroma mixed with tumor had intact overlying fat, but the nodule lacked a radiolucent center and was not close to the carotid artery.

CONCLUSION

The CT findings of a stable nodule that is posterior but close to the carotid artery with central radiolucency, a dense rim, and intact overlying fat, combined with the clinical features of a trigger point and a lack of interval growth, strongly suggest the diagnosis of traumatic neuroma.

Normal anatomy of the neck with CT and MR imaging correlation

Knowledge of normal anatomy is the cornerstone for understanding pathologic processes. Often, the most difficult task for a radiologist is differentiating normal structures from pathology. There are many ways to organize a discussion of the normal anatomy in the neck. This article is organized by organ system, with an additional discussion of triangles, fascia, and spaces. Important normal variants are also discussed.

The CT appearance of thyroglossal duct carcinoma

BACKGROUND AND PURPOSE

Thyroid carcinoma arising in a thyroglossal duct cyst may be clinically indistinguishable from a benign thyroglossal duct cyst. The preoperative diagnosis of carcinoma, however, can have important implications for surgical planning and postoperative treatment. Our purpose was to describe the CT appearance of thyroglossal duct carcinoma and identify the features that distinguish thyroglossal duct carcinoma from benign thyroglossal duct cysts.

METHODS

Retrospective review of the medical records from the University of Pittsburgh Medical Center and Geisinger Medical Center (Danville, Pennsylvania) identified six patients with papillary thyroid carcinoma within the thyroglossal duct who had undergone preoperative CT examinations of the neck. There were two women and four men. Their ages ranged from 14 to 59 years. Three patients underwent contrast-enhanced CT of the neck, and three underwent unenhanced CT. All CT examinations consisted of 3- to 5-mm-thick contiguous axial sections.

RESULTS

Each patient had an anterior neck mass with a cystic component. Two of the masses had dense or enhancing mural nodules, two had irregular calcification throughout the mass, and two had dense or enhancing mural nodules with additional foci of calcification. One patient had cervical lymphadenopathy.

CONCLUSION

Carcinoma should be considered in thyroglossal duct cysts that have a mural nodule or calcification or both.

Imaging of tinnitus: a review

Tinnitus, a buzzing or ringing in the ear, may be pulsatile or continuous (nonpulsatile). The distinction, with a detailed clinical evaluation, determines the most appropriate imaging study. Pulsatile tinnitus suggests a vascular neoplasm, vascular anomaly, or vascular malformation. Most of the neoplasms are glomus tympanicum and glomus jugulare tumors. Vascular anomalies may cause pulsatile tinnitus, but the mechanism is unknown, and another (treatable) cause should be sought. Most neoplasms and anomalies are best seen on bone algorithm computed tomographic (CT) studies. Dural vascular malformations are often elusive on all cross-sectional imaging studies; conventional angiography may be necessary to make this diagnosis. Flow-sensitive magnetic resonance (MR) images show vascular loops compressing the eighth cranial nerve. Carotid dissections, aneurysms, atherosclerosis, and fibromuscular dysplasia can be identified on both MR imaging or MR angiographic studies and CT or CT angiographic studies. Otosclerosis and Paget disease are CT diagnoses. Benign intracranial hypertension often has no abnormal imaging findings. For patients with nonpulsatile tinnitus, MR imaging is the study of choice to exclude a vestibular schwannoma or other neoplasm of the cerebellopontine angle cistern. Multiple sclerosis and a Chiari I malformation are rare causes of pulsatile tinnitus, also best seen on MR studies. Many patients with tinnitus have no abnormal imaging findings.

MR imaging of intraventricular silicone: case report

A 42-year-old man with human immunodeficiency viral infection developed cytomegaloviral retinitis that was complicated by retinal detachment and was treated with an intravitreous injection of silicone. Fifteen months later, magnetic resonance imaging revealed intraocular and intraventricular silicone. Signal intensity characteristics and chemical shifts of silicone in the two locations were identical.

Current imaging techniques for head and neck tumors

Modern head and neck imaging has led to advances in both the diagnosis and treatment of head and neck cancers. Both computed tomography (CT) and magnetic resonance imaging (MRI) studies provide important information about the location and extent of neoplasm, particularly with respect to the interface of tumor with bone, fat, muscles and other soft tissues, air, blood vessels, dura, and brain. Conventional angiography can be used to assess tumor blood supply and vascularity and to perform therapeutic embolization. Magnetic resonance angiography (MRA) and CT angiography (CTA) are new tools for the noninvasive evaluation of blood vessels. Positron emission tomography (PET) shows promise for differentiating tumor from scar, edema, and other nonneoplastic soft tissues.

Imaging of a Stafne bone cavity: what MR adds and why a new name is needed

Stafne bone cavities are asymptomatic radiolucencies seen at the angle of the mandible. Although plain films are often sufficient for diagnosis, confirmatory imaging is needed in atypical cases. We describe the MR imaging findings of a Stafne bone cavity, describe the contents, explain why a new name is needed, and discuss the relative merits of different radiologic techniques for establishing this diagnosis.

Imaging of Bezold's abscess

OBJECTIVE

Our purpose was to describe the CT findings in patients with Bezold's abscesses.

CONCLUSION

Bezold's abscesses are rare complications of mastoiditis. In our series most were seen in adults and were associated with a history of cholesteatoma and mastoidectomy. CT of the neck and temporal bone can help the surgeon determine appropriate treatment.

Anterior facial vein and submandibular gland together: predicting the histology of submandibular masses with CT or MR imaging

PURPOSE

To test the hypothesis that the relationship of the anterior facial vein to the submandibular salivary gland and a mass in the submandibular fossa could help identify the origin of the mass at computed tomography (CT) or magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Thirteen patients with 14 palpable submandibular masses, surgical and histologic confirmation, and contrast material-enhanced CT images (12 patients) or MR images (one patient) that showed the anterior facial vein were identified with review of files from 1985 to 1997. Six patients had submandibular gland disease: three with primary neoplasms, two with metastatic tumor invading the gland, and one with chronic sialoadenitis. Eight patients had masses arising outside the gland (seven with lymphadenopathy, one with a plexiform neurofibroma).

RESULTS

The anterior facial vein did not separate primary tumors, tumors invading the gland, or lobulations of the enlarged gland from the body of the gland. The vein was identified between enlarged lymph nodes and the gland. The vein did not separate the gland from the neurofibroma, but this tumor was medial to the gland; the vein runs lateral to the gland.

CONCLUSION

The anterior facial vein is a useful landmark in determining the origin of a submandibular mass. Primary disease of the gland is never separated from the gland by the vein. The vein does separate lymphadenopathy from the gland and, theoretically, separates the gland from soft-tissue tumors lateral to the gland.

Thyroid gland after total laryngectomy: CT appearance

PURPOSE

To determine the computed tomographic (CT) appearance of the normal thyroid gland after total laryngectomy, because the high attenuation (or heterogeneous attenuation) of thyroid parenchyma was misinterpreted as tumor on several CT studies.

MATERIALS AND METHODS

A search of computerized clinical files compiled from January 1996 through August 1997 yielded data on 24 patients who had undergone laryngectomy and subsequent CT of the neck. From these 24 patients, CT findings were available in 21. Because one patient had undergone total thyroidectomy and was excluded from the study, a retrospective review was performed in the remaining 20 patients.

RESULTS

In 14 patients, unilateral thyroid tissue was present; in the other six there was bilateral thyroid tissue not connected by an isthmus. Thus, there were 26 remaining thyroid lobes, of which six were round and 20 were oval or lobular. Nineteen lobes showed homogeneously high attenuation (including one scanned without use of contrast material), six showed heterogeneous high attenuation or contained areas of hyperlucency, and one was obscured by streak artifact.

CONCLUSION

Thyroid tissue can appear as unilateral or bilateral asymmetric masses on neck CT scans after laryngectomy. Gland tissue can show homogeneously or heterogeneously high attenuation. Familiarity with the varied postoperative appearance of normal thyroid gland can prevent its misdiagnosis as tumor.

Intranasal endoscopic excision of a juvenile angiofibroma

Intranasal endoscopic excision of a juvenile nasopharyngeal angiofibroma (JNA) was performed in a 13 year old white male. The patient remains disease-free 24 months after the operation. Although endoscopic surgical techniques have been applied to the therapy of some benign nasal tumors, such as inverting papilloma, endoscopic resection of a documented JNA has not been previously reported. This technique is reserved for tumors which are limited to the nasal cavity and paranasal sinuses with minimal extension into the pterygopalatine fossa.

Beyond the promontory: the multifocal origin of glomus tympanicum tumors

PURPOSE

We examined other middle ear locations of glomus tympanicum tumors, which arise from glomus bodies accompanying the tympanic (Jacobson's) nerve through the middle ear. Most descriptions place these tumors on the promontory over the basal turn of the cochlea.

METHODS

We identified seven patients (all women) with small surgically confirmed glomus tympanicum tumors (not completely filling the middle ear) for whom CT scans were available for retrospective review. Patients' ages ranged from 23 to 78 years at the time of the high-resolution CT study (1.0- to 1.5-mm-thick sections).

RESULTS

All tumors arose on the medial wall of the middle ear. One was anterior to the promontory, beneath the cochleariform process and the semicanal of the tensor tympani. Two were inferior to the promontory, in the recess beneath the basal turn of the cochlea. Four were anteroinferior. None was actually on the apex of the promontory.

CONCLUSION

Glomus tympanicum tumors may arise in various locations on the medial wall of the middle ear, where Jacobson's nerve runs. The promontory is only one middle ear location in which glomus tympanicum tumors may arise. Familiarity with the course of the tympanic nerve helps tailor the search for, and facilitates accurate identification of, tiny glomus tympanicum tumors.

Imaging of Meniere's disease

The role of CT and MR studies in the evaluation of patients with Meniere's disease is to exclude other pathologic conditions that could masquerade as Meniere's disease clinically. This article is divided into three sections corresponding to the three major symptoms of Meniere's disease. Each section presents examples of CT and MR pathologic conditions that could mimic these clinical findings: "sensorineural hearing loss" covers acoustic neuromas and other cerebellopontine angle tumors, inner ear anomalies, otosclerosis, and more; "vertigo" includes examples of labyrinthitis, endolymphatic sac tumor, cholesteatomatous fistula, and brain metastasis; and "tinnitus" emphasizes causes of nonpulsatile tinnitus and briefly mentions pulsatile tinnitus. Each section also discusses which imaging study best addresses these specific clinical questions.

MR appearance of trigeminal and hypoglossal motor denervation

PURPOSE

To illustrate and describe the appearance of both long-standing and relatively recently occurring motor denervation of the hypoglossal nerve and of the third (mandibular) division of the trigeminal nerve (V3), with emphasis on findings particular to MR imaging.

METHODS

Findings from 11 patients with V3 denervation and from seven patients with hypoglossal denervation resulting from a variety of abnormalities were reviewed retrospectively. The motor denervation appearance and functional compromise of the affected musculature are described in terms of the chronicity of the denervation process.

RESULTS

The appearance of V3 and hypoglossal motor denervation varies with the chronicity of the process. Long-standing denervation results in extensive fatty replacement and a decrease in the size of the affected musculature. Relatively recently occurring denervation results in abnormal contrast enhancement and edemalike signal changes in the denervated musculature. Fatty replacement was observed acutely in hypoglossal denervation but did not manifest until the subacute stage in V3 denervation. Increased volume of the denervated musculature may also accompany acute denervation signal changes.

CONCLUSION

V3 and hypoglossal denervation have a variable appearance depending on the chronicity of the process. Recognition of MR imaging patterns of denervation may allow earlier diagnosis of a denervating lesion and may help to distinguish denervation from similar-appearing processes, such as infection or neoplasia.

Neurilemomas of the parapharyngeal space

OBJECTIVE

To review the surgical management of neurilemomas of the parapharyngeal space (PPS).

DESIGN

Retrospective survey of the clinical presentation, radiological features, surgical approaches, surgical findings, and postoperative neurological sequelae of neurilemomas of the PPS.

SETTING

Academic tertiary care head and neck referral center.

PATIENTS

Fourteen patients with neurilemomas of the PPS, 12 were in the poststyloid compartment.

INTERVENTIONS

Preoperative evaluation with computed tomography and/or magnetic resonance imaging with or without angiography. Surgical resection was performed through a transcervical approach.

MAIN OUTCOME MEASURES

Radiological features, adequacy of surgical approach, and neurological sequelae of surgery.

RESULTS

Radiological studies could distinguish prestyloid from poststyloid tumors and, with poststyloid tumors, can usually differentiate between glomus tumor and neurilemoma. The transcervical approach permitted adequate surgical access. Five of the tumors in the poststyloid space were neurilomomas originating from the sympathetic nervous system, and all 5 patients with these tumors developed Horner syndrome postoperatively.

CONCLUSIONS

Computed tomographic and/or magnetic resonance studies should be routinely obtained to evaluate tumors of the PPS, but angiography is indicated only in selected cases. Both prestyloid and poststyloid neurilemomas can be resected through a transcervical approach. Resection of neurilemomas has an attendant risk for neurological dysfunction.

Papillary endolymphatic sac tumors: CT, MR imaging, and angiographic findings in 20 patients

PURPOSE

To determine the computed tomographic (CT), magnetic resonance (MR) imaging, and angiographic findings of papillary endolymphatic sac tumors.

MATERIALS AND METHODS

Clinical and imaging studies in 20 patients (aged 17-65 years) with histopathologically proved papillary endolymphatic sac tumors were retrospectively reviewed. Patients underwent CT (n = 18), MR imaging (n = 15), or angiography (n = 12). CT scans were evaluated for bone erosion and calcification; MR images, for signal intensity, enhancement patterns, and flow voids; and angiograms, for tumoral blood supply.

RESULTS

All tumors were destructive and contained calcifications centered in the retrolabyrinthine region at CT. The MR imaging appearance varied with lesion size; 12 of 15 tumors showed increased signal intensity at T1-weighted imaging. The high-signal-intensity area was circumferential in lesions 3 cm or smaller and was scattered throughout the lesion in advanced tumors. Only tumors larger than 2 cm had flow voids. The blood supply arose predominantly from the external carotid artery. Large tumors had additional supply from the internal carotid and posterior circulation.

CONCLUSION

Papillary endolymphatic sac tumors are destructive, hypervascular lesions that arise from the temporal bone retrolabyrinthine region. Increased signal intensity at unenhanced T1-weighted MR imaging is common and may help distinguish these lesions from more common, aggressive temporal bone tumors.

The evolving MR appearance of structures in the internal auditory canal after removal of an acoustic neuroma

PURPOSE

To identify patterns of enhancement in the internal auditory canal (IAC) on MR studies after removal of an acoustic neuroma, including changes in those patterns with time; to evaluate signal and enhancement of the labyrinth; to differentiate normal postoperative findings from those suggesting residual tumor; and to describe MR hallmarks of surgical approaches.

METHODS

We reviewed the postoperative MR studies obtained in 36 patients who had had surgery for acoustic neuroma (101 images total). Four patterns of IAC enhancement were evaluated, as was labyrinthine signal intensity before and after contrast administration, changes in findings over time, and anatomic alterations caused by surgery.

RESULTS

All patients had enhancement of the IAC on the first postoperative study. In 30 patients, IAC enhancement remained the same or decreased over time. Seventeen patients had hyperintense cochlear signal and 15 had cochlear enhancement that decreased with time. Effects of retrosigmoid craniotomy, a translabyrinthine surgical approach, and middle fossa craniotomy were recognizable.

CONCLUSION

Linear enhancement in the IAC is probably normal after surgery. Nodular and masslike enhancement and any progressive enhancement may require close follow-up to monitor growth of residual tumor. Labyrinthine hyperintensity may reflect blood metabolites. An MR protocol is suggested for following up patients in the years after surgery.

Reconstructive myofascial skull-base flaps: normal appearance on CT and MR imaging studies

On imaging studies, the tendon and fractured coronoid process are clues to the presence of a temporalis myofascial flap. A large, bulky muscle and subcutaneous fat are characteristic of a free flap with microvascular anastomosis. The enhancing, thin, curvilinear pericranial flap bridges an osseous defect of the anterior skull base. Familiarity with these features is essential to avoid misdiagnosis of normal flap as tumor and to identify tumor recurrence.

Hydroxyapatite cement to repair skull base defects: radiologic appearance

PURPOSE

To describe the radiologic appearance of hydroxyapatite cement (HAC), which, when mixed with liquid, forms a paste that can be contoured to osseous defects and, over time, becomes "osseointegrated" (native bone grows into the pores of the HAC and forms a strong chemical bond with the substance).

METHODS

Between March 1992 and June 1993, 24 adults (16 men, eight women) underwent skull base surgery that included reconstruction or closure with HAC. Fourteen patients had HAC placed in the paranasal sinuses or facial bones, and 10 had HAC placed in the mastoid cavity.

RESULTS

HAC is homogeneously radiopaque on CT scans and plain radiographs. Large amounts (ablating a frontal sinus or mastoid air cells) are readily seen; small amounts are inconspicuous. On MR images, HAC is a signal void. Infected HAC in one patient was surrounded be enhancing soft tissue on MR images, separated from native bone by an irregular radiolucent cleft on CT scans.

CONCLUSIONS

HAC is a valuable addition to the surgical armamentarium for the repair of skull base defects. More experience will determine the time course for normal osseointegration, as well as the typical appearance of infection.

T2-weighted MR characteristics of internal auditory canal masses

PURPOSE

To determine whether masses of the internal auditory canal are hypointense relative to cerebrospinal fluid, and therefore visible, on fast spin-echo T2-weighted MR images.

METHODS

Forty-six patients had 50 masses of the internal auditory canal, identified initially on contrast-enhanced MR images, that were evaluated retrospectively for signal intensity of the mass with respect to cerebrospinal fluid and for visibility of the neural elements within the internal auditory canal on T2-weighted images.

RESULTS

Forty-seven of 50 masses were clearly identified on T2-weighted images. Three small abnormalities (2 to 4 mm) were not seen with confidence on T2-weighted images. However, on close inspection of these three masses, the small abnormality on contrast-enhanced MR images corresponded to a hypointense focus on T2-weighted images. All 50 masses were hypointense relative to cerebrospinal fluid on T2-weighted images.

CONCLUSION

All masses of the internal auditory canal in this study were hypointense relative to cerebrospinal fluid on T-2 weighted images, and were therefore visible.

Chondrosarcoma of the nasal septum: skull base imaging and clinicopathologic correlation

Chondrosarcoma arising in the head and neck and craniofacial region is an uncommon lesion. The nasal septum is a particularly rare site of origin, with approximately 30 cases previously reported in the English literature. We present six new cases of chondrosarcoma arising in the nasal septum. Each of these tumors required cranial base surgical approaches for removal. Current imaging techniques allow a very accurate diagnosis to be made before biopsy. The characteristic ring-forming calcifications seen on computed tomography scans can be correlated with the histologic pattern of calcification. Magnetic resonance imaging techniques allow precise definition of tumor extent, which is particularly important because the disease is best treated with primary surgery. Advances in imaging and surgical techniques allow a much more complete tumor removal. It is hoped that this will increase the likelihood of cure in these patients. Surgical management and indications for adjuvant therapy are discussed.

Hearing loss

Nearly 30 million Americans have hearing loss. Audiograms are used to determine if hearing loss is sensorineural (SNHL), conductive (CHL), or mixed (MHL). SNHL indicates dysfunction of the cochlea, cochlear nerve, or brain. The study of choice for adults with SNHL is gadolinium-enhanced magnetic resonance imaging, which is used to look for acoustic neuromas, abnormal labyrinth signal intensity or enhancement, and brain disease. In children with SNHL, computed tomography (CT) performed with bone algorithms demonstrates inner ear dysplasias. SNHL from trauma is best evaluated with CT studies. CHL indicates disease in the external auditory canal, tympanic membrane, or middle ear; CT with thin bone algorithms is the best study. Causes of CHL include external canal atresia and neoplasms, myringosclerosis, middle ear anomalies, effusion, cholesteatomas, and neoplasms. MHL is a combination of SNHL and CHL. Dysplasias such as otosclerosis and osteogenesis imperfecta, the most frequent diseases with radiologic findings, are best assessed on CT images. The combination of patient age and type of hearing loss determines the best imaging study.

Computer-assisted intraoperative navigation during skull base surgery

PURPOSE

In patients with diseases of the cranial base, anatomical landmarks are often obliterated by tumor inflammatory diseases or previous surgery. The surgeon may fail to recognize important anatomical structures or tumor margins, increasing the morbidity of the surgery and downgrading the oncological outcome.

MATERIALS AND METHODS

The ISG Viewing Wand is an intraoperative navigational device that uses a position-sensing articulated arm linked to a computer that allows the surgeon to correlate the anatomy of the patient with the computerized display of the reformatted images of preoperative computerized tomography or magnetic resonance. We used the ISG system in 20 patients undergoing skull base surgery for the treatment of tumor inflammatory diseases and trauma.

RESULTS

The use of the ISG wand translated into a decreased need for the resection of vital structures and provided reliable mapping of the boundaries of the paranasal sinuses and tumor margins.

CONCLUSION

Intraoperative navigation is a promising technology that complements the surgeon's interpretation of the surgical field. Further refinements of this technology will ease the incorporation of these intraoperative navigation systems into other surgical procedures.