Central Connection of the Optic, Oculomotor, Trochlear and Abducens Nerves in Medaka, Oryzias latipes

Medaka (Oryzias latipes) is one of the few vertebrate experimental animals in which inbred lines have been established. It is also a species that has advanced in genetic studies in a manner comparable to zebrafish. This fish is therefore a good model for studying functional organization of the nervous system, but anatomical analysis of its nervous system has been limited to embryonic stages. In the present study, we investigated anatomy of cranial nerves in adult fish focusing on the visual function, using an inbred strain of medaka. Cranial nerves of medaka were labeled using biocytin, revealing a central distribution of retinofugal terminals, retinopetal neurons, and oculomotor, trochlear and abducens motor neurons. The optic nerve of the adult medaka was of a complete decussation type. Retinofugal terminals were located in 8 brain nuclei, the suprachiasmatic nucleus, nucleus pretectalis superficialis, nucleus dorsolateralis thalami, area pretectalis pars dorsalis (APd), area pretectalis pars ventralis (APv), nucleus of the posterior commissure (NPC), accessory optic nucleus, and the tectum opticum. Retinopetal neurons were identified in 6 brain nuclei, the ganglion of the terminal nerve, preoptic retinopetal nucleus, nucleus dorsolateralis thalami, APd, APv, and NPC. The oculomotor neurons were mostly labeled ipsilaterally and were located dorsomedially, abutting the fasciculus longitudinalis medialis in the mesencephalon. The trochlear nucleus was located contralaterally and dorsolaterally adjacent to the fasciculus longitudinalis medialis in the mesencephalon. The abducens nucleus was located ipsilaterally in a ventrolateral part of the rhombencephalic reticular formation. These results, generally similar to those in other teleosts, provide the basis for future behavioral and genetic studies in medaka.

Mutations affecting the formation of posterior lateral line system in Medaka, Oryzias latipes

We performed a systematic screen for mutations affecting the trajectory of axons visualized by immunohistochemical staining of Medaka embryos with anti-acetylated tubulin antibody. Among the mutations identified, yanagi (yan) and kazura (kaz) mutations caused specific defects in projection of the posterior lateral line (PLL) nerve. In yan and kaz mutant embryos, the PLL nerve main bundle was misrouted ventrally and dorsally or anteriorly. Medaka semaphorin3A, sdf1, and cxcr4 cDNA fragments were cloned to allow analysis of these mutants. There were no changes in semaphorin3A or sdf1 expression in mutant embryos, suggesting that the tissues expressing semaphorin3A or sdf1 that are involved in PLL nerve guidance are present in these mutant embryos. Double staining revealed that the mislocated PLL primordium and growth cone of the ectopically projected PLL nerve were always colocalized in both yan and kaz mutant embryos, suggesting that migration of PLL primordia and PLL nerve growth cones are not uncoupled in these mutants. Although homozygous yan larvae showed incomplete migration of the PLL primordium along the anteroposterior axis, ventral proneuromast migration was complete, suggesting that ventral migration of the proneuromast does not require the signaling affected in yan mutants. In addition to the PLL system, the distribution of primordial germ cells (PGCs) was also affected in both yan and kaz mutant embryos, indicating that yan and kaz genes are required for the migration of both PLL primordia and PGCs. Genetic linkage analysis indicated that kaz is linked to cxcr4, but yan is not linked to sdf1 or cxcr4. These mutations will provide genetic clues to investigate the molecular mechanism underlying formation of the PLL system.

A systematic genome-wide screen for mutations affecting organogenesis in Medaka, Oryzias latipes

A large-scale mutagenesis screen was performed in Medaka to identify genes acting in diverse developmental processes. Mutations were identified in homozygous F3 progeny derived from ENU-treated founder males. In addition to the morphological inspection of live embryos, other approaches were used to detect abnormalities in organogenesis and in specific cellular processes, including germ cell migration, nerve tract formation, sensory organ differentiation and DNA repair. Among 2031 embryonic lethal mutations identified, 312 causing defects in organogenesis were selected for further analyses. From these, 126 mutations were characterized genetically and assigned to 105 genes. The similarity of the development of Medaka and zebrafish facilitated the comparison of mutant phenotypes, which indicated that many mutations in Medaka cause unique phenotypes so far unrecorded in zebrafish. Even when mutations of the two fish species cause a similar phenotype such as one-eyed-pinhead or parachute, more genes were found in Medaka than in zebrafish that produced the same phenotype when mutated. These observations suggest that many Medaka mutants represent new genes and, therefore, are important complements to the collection of zebrafish mutants that have proven so valuable for exploring genomic function in development.

Mutations affecting thymus organogenesis in Medaka, Oryzias latipes

The thymus is an organ for T lymphocyte maturation and is indispensable for the establishment of a highly developed immune system in vertebrates. In order to genetically dissect thymus organogenesis, we carried out a large-scale mutagenesis screening for Medaka mutations affecting recombination activating gene 1 (rag1) expression in the developing thymus. We identified 24 mutations, defining at least 13 genes, which led to a marked reduction of rag1 expression in the thymus. As thymus development depends on pharyngeal arches, we classified those mutations into three classes according to the defects in the pharyngeal arches. Class 1 mutants had no or slight morphological abnormalities in the pharyngeal arches, implying that the mutations may include defects in such thymus-specific events as lymphocyte development and thymic epithelial cell maturation. Class 2 mutants had abnormally shaped pharyngeal arches. Class 3 mutants showed severely attenuated pharyngeal arch development. In Class 2 and Class 3 mutants, the defects in thymus development may be due to abnormal pharyngeal arch development. Those mutations are expected to be useful for identifying the molecular mechanisms underlying thymus organogenesis.

Mutations affecting early distribution of primordial germ cells in Medaka (Oryzias latipes) embryo

The development of germ cells has been intensively studied in Medaka (Oryzias latipes). We have undertaken a large-scale screen to identify mutations affecting the development of primordial germ cells (PGCs) in Medaka. Embryos derived from mutagenized founder fish were screened for an abnormal distribution or number of PGCs at embryonic stage 27 by RNA in situ hybridization for the Medaka vasa homologue (olvas). At this stage, PGCs coalesce into two bilateral vasa-expressing foci in the ventrolateral regions of the trunk after their migration and group organization. Nineteen mutations were identified from a screen corresponding to 450 mutagenized haploid genomes. Eleven of the mutations caused altered PGC distribution. Most of these alterations were associated with morphological abnormalities and could be grouped into four phenotypic classes: Class 1, PGCs dispersed into bilateral lines; Class 2, PGCs dispersed in a region more medial than that in Class 1; Class 3, PGCs scattered laterally and over the yolk sac area; and Class 4, PGCs clustered in a single median focus. Eight mutations caused a decrease in the number of PGCs. This decrease was observed in the offspring of heterozygous mothers, indicating the contribution of a maternal factor in determining PGC abundance. Taken together, these mutations should prove useful in identifying molecular mechanisms underlying the early PGC development and migration.

Genetic dissection of the formation of the forebrain in Medaka, Oryzias latipes

The forebrain, consisting of the telencephalon and diencephalon, is essential for processing sensory information. To genetically dissect formation of the forebrain in vertebrates, we carried out a systematic screen for mutations affecting morphogenesis of the forebrain in Medaka. Thirty-three mutations defining 25 genes affecting the morphological development of the forebrain were grouped into two classes. Class 1 mutants commonly showing a decrease in forebrain size, were further divided into subclasses 1A to 1D. Class 1A mutation (1 gene) caused an early defect evidenced by the lack of bf1 expression, Class 1B mutations (6 genes) patterning defects revealed by the aberrant expression of regional marker genes, Class 1C mutation (1 gene) a defect in a later stage, and Class 1D (3 genes) a midline defect analogous to the zebrafish one-eyed pinhead mutation. Class 2 mutations caused morphological abnormalities in the forebrain without considerably affecting its size, Class 2A mutations (6 genes) caused abnormalities in the development of the ventricle, Class 2B mutations (2 genes) severely affected the anterior commissure, and Class 2C (6 genes) mutations resulted in a unique forebrain morphology. Many of these mutants showed the compromised sonic hedgehog expression in the zona-limitans-intrathalamica (zli), arguing for the importance of this structure as a secondary signaling center. These mutants should provide important clues to the elucidation of the molecular mechanisms underlying forebrain development, and shed new light on phylogenically conserved and divergent functions in the developmental process.

Mutations affecting retinotectal axonal pathfinding in Medaka, Oryzias latipes

We screened for mutations affecting retinotectal axonal projection in Medaka, Oryzias latipes. In wild-type Medaka embryos, all the axons of retinal ganglion cells (RGCs) project to the contralateral tectum, such that the topological relationship of the retinal field is maintained. We labeled RGC axons using DiI/DiO at the nasodorsal and temporoventral positions of the retina, and screened for mutations affecting the pattern of stereotypic projections to the tectum. By screening 184 mutagenized haploid genomes, seven mutations in five genes causing defects in axonal pathfinding were identified, whereas mutations affecting the topographic projection of RGC axons were not found. The mutants were grouped into two classes according to their phenotypes. In mutants of Class I, a subpopulation of the RGC axons branched out either immediately after leaving the eye or after reaching the midline, and this axonal subpopulation projected to the ipsilateral tectum. In mutants of Class II, subpopulations of RGC axons branched out after crossing the midline and projected aberrantly. These mutants will provide clues to understanding the functions of genes essential for axonal pathfinding, which may be conserved or partly divergent among vertebrates.

Mutations affecting gonadal development in Medaka, Oryzias latipes

A gonad is formed from germ cells and somatic mesodermal cells through their interactions. Its development is coupled with the determination and differentiation of the sex and sex-associated traits. We carried out a large-scale screening of Medaka mutants in which gonadal development is affected. Screening was performed on larvae at 8 days posthatching for abnormal abundance and/or distribution of germ cells detected by the in situ hybridization for olvas (Medaka vasa). We describe here 16 mutants of 13 genes, which are classified into four groups. Group 1, consisting of four mutants of three genes kon, tot) characterised by an increase in germ cell number. An adult tot homozygote fish has the characteristic feature of possessing hypertrophic gonads filled with immature oocytes. Group 2, represented by a single gene (zen) mutant characterized by a gradual loss of germ cells. Group 3, consisting of four mutants of distinct genes (eko, eki, sht, ano) showing irregular clustering of germ cells. Group 4, consisting of seven mutants of five genes (arr, hyo, mzr, hdr, fbk) showing fragmented clusters of germ cells. In some mutants belonging to Groups 1, 3 and 4, the expression level of ftz-f1 (sf-1/Ad4BP) in gonadal somatic cells significantly decreased, suggesting that interaction between somatic and germ cells is affected.

Identification of radiation-sensitive mutants in the Medaka, Oryzias latipes

We screened populations of N-ethyl-N-nitrosourea (ENU)-mutagenized Medaka, (Oryzias latipes) for radiation-sensitive mutants to investigate the mechanism of genome stability induced by ionizing radiation in developing embryos. F3 embryos derived from male founders that were homozygous for induced the mutations were irradiated with gamma-rays at the organogenesis stage (48hpf) at a dose that did not cause malformation in wild-type embryos. We screened 2130 F2 pairs and identified three types of mutants with high incidence of radiation-induced curly tailed (ric) malformations using a low dose of irradiation. The homozygous strain from one of these mutants, ric1, which is highly fertile and easy to breed, was established and characterized related to gamma-irradiation response. The ric1 strain also showed higher incidence of malformation and lower hatchability compared to the wild-type CAB strain after gamma-irradiation at the morula and pre-early gastrula stages. We found that the decrease in hatching success after gamma-irradiation, depends on the maternal genotype at the ric1 locus. Terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end-labeling assays showed a high frequency of apoptosis in the ric1 embryos immediately after gamma-irradiation at the pre-early gastrula stage but apoptotic cells were not observed before midblastula transition (MBT). The neutral comet assay revealed that the ric1 mutant has a defect in the rapid repair of DNA double-strand breaks induced by gamma-rays. These results suggest that RIC1 is involved in the DNA double strand break repair in embryos from morula to organogenesis stages, and unrepaired DNA double strand breaks in ric1 trigger apoptosis after MBT. These results support the use of the ric1 strain for investigating various biological consequences of DNA double strand breaks in vivo and for sensitive monitoring of genotoxicity related to low dose radiation.

Mutations affecting retina development in Medaka

In a large scale mutagenesis screen of Medaka we identified 60 recessive zygotic mutations that affect retina development. Based on the onset and type of phenotypic abnormalities, the mutants were grouped into five categories: the first includes 11 mutants that are affected in neural plate and optic vesicle formation. The second group comprises 15 mutants that are impaired in optic vesicle growth. The third group includes 18 mutants that are affected in optic cup development. The fourth group contains 13 mutants with defects in retinal differentiation. 12 of these have smaller eyes, whereas one mutation results in enlarged eyes. The fifth group consists of three mutants with defects in retinal pigmentation. The collection of mutants will be used to address the molecular genetic mechanisms underlying vertebrate eye formation.

Mutations affecting liver development and function in Medaka, Oryzias latipes, screened by multiple criteria

We report here mutations affecting various aspects of liver development and function identified by multiple assays in a systematic mutagenesis screen in Medaka. The 22 identified recessive mutations assigned to 19 complementation groups fell into five phenotypic groups. Group 1, showing defective liver morphogenesis, comprises mutations in four genes, which may be involved in the regulation of growth or patterning of the gut endoderm. Group 2 comprises mutations in three genes that affect the laterality of the liver; in kendama mutants of this group, the laterality of the heart and liver is uncoupled and randomized. Group 3 includes mutations in three genes altering bile color, indicative of defects in hemoglobin-bilirubin metabolism and globin synthesis. Group 4 consists of mutations in three genes, characterized by a decrease in the accumulation of fluorescent metabolite of a phospholipase A(2) substrate, PED6, in the gall bladder. Lipid metabolism or the transport of lipid metabolites may be affected by these mutations. Mutations in Groups 3 and 4 may provide animal models for relevant human diseases. Group 5 mutations in six genes affect the formation of endoderm, endodermal rods and hepatic bud from which the liver develops. These Medaka mutations, identified by morphological and metabolite marker screens, should provide clues to understanding molecular mechanisms underlying formation of a functional liver.

Mutations affecting somite formation in the Medaka (Oryzias latipes)

The metameric structure of the vertebrate trunk is generated by repeated formation of somites from the unsegmented presomitic mesoderm (PSM). We report the initial characterization of nine different mutants affecting segmentation that were isolated in a large-scale mutagenesis screen in Medaka (Oryzias latipes). Four mutants were identified that show a complete or partial absence of somites or somite boundaries. In addition, five mutations were found that cause fused somites or somites with irregular sizes and shapes. In situ hybridization analysis using specific markers involved in the segmentation clock and antero-posterior (A-P) polarity of somites revealed that the nine mutants can be compiled into two groups. In group 1, mutants exhibit defects in tailbud formation and PSM prepatterning, whereas A-P identity in the somites is defective in group 2 mutants. Three mutants (planlos, pll; schnelles ende, sne; samidare, sam) have characteristic phenotypes that are similar to those in zebrafish mutants affected in the Delta/Notch signaling pathway. The majority of mutants, however, exhibit somitic phenotypes distinct from those found in zebrafish, such as individually fused somites and irregular somite sizes. Thus, these Medaka mutants can be expected to provide clues to uncovering novel components essential for somitogenesis.

Galanin-immunoreactive nerve fibers in the periodontal ligament during experimental tooth movement

Neuropeptides have been suggested to play a role in pain transmission during orthodontic tooth movement. We examined this hypothesis by examining the effect of orthodontic tooth movement on the expression of galanin (GAL)-immunoreactive (ir) nerve fibers in the periodontal ligament (PDL) of one mesial root (MR) and two distal roots (DRs) of the rat maxillary first molar. In control rats, GAL-ir fibers were very rare in the PDL. One day after the insertion of the elastic band, the number of GAL-ir fibers increased, becoming most numerous at 3 days. From 5 to 28 days, GAL-ir fibers tended to decrease. Electron microscopic observation showed that all of the GAL-ir fibers were unmyelinated. These findings suggest that GAL-containing nerve fibers in the PDL may play an important role in the response of the tissue to experimental tooth movement.

The use of small titanium screws for orthodontic anchorage

The use of conventional dental implants for orthodontic anchorage is limited by their large size. The purpose of this study was to quantify the histomorphometric properties of the bone-implant interface to analyze the use of small titanium screws as an orthodontic anchorage and to establish an adequate healing period. Overall, successful rigid osseous fixation was achieved by 97% of the 96 implants placed in 8 dogs and 100% of the elastomeric chain-loaded implants. All of the loaded implants remained integrated. Mandibular implants had significantly higher bone-implant contact than maxillary implants. Within each arch, the significant histomorphometric indices noted for the "three-week unloaded" healing group were: increased labeling incidence, higher woven-to-lamellar-bone ratio, and increased osseous contact. Analysis of these data indicates that small titanium screws were able to function as rigid osseous anchorage against orthodontic load for 3 months with a minimal (under 3 weeks) healing period.

Craniofacial morphology of Japanese girls with Class II division 1 malocclusion

OBJECTIVE

To identify the craniofacial features of Japanese girls with Class II division 1 malocclusions.

METHOD

One hundred and ninety lateral cephalometric radiographs were analysed, and the subjects whose age ranged from 7 years 6 months to 15 years 10 months were divided into three groups by their dentition: middle mixed dentition, late mixed dentition, and early permanent dentition. The mean values of 5 linear and 16 angular cephalometric parameters were compared with established Japanese Class I control values.

RESULTS

Japanese girls with Class II division 1 malocclusion had a significantly small S-N-B angle (p < 0.001), short mandibular ramus (p < 0.05-0.001), and a large mandibular plane angle (p < 0.05-0.001).

CONCLUSION

Japanese girls with Class II division 1 malocclusion had a high-angle facial pattern associated with the short mandibular ramus.

Gyration radius of a circular polymer under a topological constraint with excluded volume

It is nontrivial whether the average size of a ring polymer should become smaller or larger under a topological constraint. Making use of some knot invariants, we numerically evaluate the mean-square radius of gyration for ring polymers having a fixed knot type, where the ring polymers are given by self-avoiding polygons consisting of freely jointed hard cylinders. We obtain plots of the gyration radius versus the number of polygonal nodes for the trivial, trefoil, and figure-eight knots. We discuss possible asymptotic behaviors of the gyration radius under the topological constraint. In the asymptotic limit, the size of a ring polymer with a given knot is larger than that of no topological constraint when the polymer is thin, and the effective expansion becomes weak when the polymer is thick enough.

Association of Mycoplasma genitalium persistence in the urethra with recurrence of nongonococcal urethritis

BACKGROUND

Most patients with recurrent symptomatic nongonococcal urethritis receive negative test results for Chlamydia trachomatis and Ureaplasma urealyticum, and the cause of such recurrence usually is unknown.

GOAL

To assess the association of Mycoplasma genitalium with recurrent nongonococcal urethritis.

STUDY DESIGN

In this study, 72 men with nongonococcal urethritis were treated with levofloxacin. Before and after treatment, symptoms and signs were assessed and first-pass urine was examined for C trachomatis, M genitalium, U urealyticum, and Mycoplasma hominis by polymerase chain reaction-based assays.

RESULTS

In 6 of 45 men who had no symptoms and no evidence of inflammation after treatment, nongonococcal urethritis recurred. Of these 6 men, 5 had positive test results for M genitalium before levofloxacin treatment, which remained positive afterward. After the second treatment for recurrent nongonococcal urethritis, one man was still had a positive test result for the mycoplasma and experienced a subsequent recurrence.

CONCLUSIONS

This study suggests that the persistence of M genitalium in the urethra may be associated with recurrence of nongonococcal urethritis.

Temporal changes in the distribution and number of macrophage-lineage cells in the periodontal membrane of the rat molar in response to experimental tooth movement

In order to evaluate the possible role of macrophages in the remodelling of periodontal tissue in response to tooth movement, temporal changes in the number and distribution of macrophage-lineage cells in the periodontal membrane of the rat molar tooth after experimental tooth movement were examined immunohistochemically using four anti-rat monoclonal antibodies: ED1 (anti-monocyte/macrophage-lineage cells and dendritic cells), ED2 (anti-resident macrophages), KI-M2R (anti-tissue macrophages), and OX6 (anti-class II molecules). The right maxillary first molar tooth of Wistar rats was moved mesially by a closed-coil spring for 1, 3, 5, or 7 days. Sham-treated rats wearing an inactivated appliance for each experimental period and entirely untreated rats were used as controls. Alternate horizontal serial cryostat sections were cut and incubated with antibodies to ED1, ED2, KI-M2R, and OX6. In addition, cells immunopositive for each monoclonal antibody in the periodontal membrane during tooth movement were analysed on the tension and pressure sides. In the control rats, large numbers of cells positively stained with each monoclonal antibody were distributed throughout the periodontal membrane surrounding the distobuccal root. At 1 day after experimental tooth movement, the number of immunopositive cells obtained with all four monoclonal antibodies decreased as compared with those of the control on the mesial/pressure side. During the later experimental time periods, ED1- and OX6-positive cells in the periodontal membrane of this side were significantly increased in number compared with controls, whereas the density and distribution pattern of cells positive with ED2 or KI-M2R remained unchanged. On the mesial/pressure side, which underwent hyalinization, a marked accumulation of OX6- and ED1-reactive cells, but not of ED2- or KI-M2R-reactive cells, was frequently observed in the area of the hyalinized tissue at 5-7 days after the start of tooth movement. On the distal/tension side, no particular change in the distribution of immunopositive cells obtained with any antibody was detected throughout the experimental periods, with the exception that there was a significant increase in the number of ED1-positive cells and in of OX6-positive cells at 1 and 7 days, respectively, after the start of tooth movement. These results suggest that after the start of tooth movement OX6- and ED1-positive cells, which are mostly exudative macrophages, but not ED2- and KI-M2R-positive cells, i.e., resident macrophages, may be actively engaged in bone resorption and the remodelling of tissues on the pressure side of the periodontal membrane.

In vivo selection of Pseudomonas Aeruginosa with decreased susceptibilities to fluoroquinolones during fluoroquinolone treatment of urinary tract infection

OBJECTIVES

To present a case of fluoroquinolone treatment failure in urinary tract infection caused by Pseudomonas aeruginosa, accompanied by in vivo selection of the post-treatment isolate that showed decreased susceptibilities to fluoroquinolones, and to report fluoroquinolone resistance mechanisms in the post-treatment isolate.

METHODS

A patient with urinary tract infection was treated with a suboptimal dose of a fluorinated quinolone, gatifloxacin. P. aeruginosa strains were isolated before and after fluoroquinolone treatment. The pretreatment and post-treatment isolates were examined for relatedness by arbitrarily primed polymerase chain reaction. For these isolates, the minimum inhibitory concentration of antimicrobial agents was determined and mutations in the target genes (gyrA and parC) and regulatory genes (mexR and nfxB) for drug efflux pumps were analyzed.

RESULTS

Failure of fluoroquinolone treatment of urinary tract infection was observed. The post-treatment isolate, which was assumed to be isogenic to the pretreatment isolate, exhibited fourfold to 16-fold increases in the MIC of fluoroquinolones. In this isolate, a new mutation, not observed in the pretreatment isolate, was found only in the gyrA gene, resulting in an amino acid change of aspartic acid to asparagine in codon 87 of GyrA.

CONCLUSIONS

The P. aeruginosa isolate that was initially susceptible to fluoroquinolones showed decreased susceptibility to fluoroquinolones after treatment with a suboptimal dose of one fluoroquinolone. In the post-treatment isolate, the alteration of GyrA would be responsible for the decreased susceptibility to fluoroquinolones. We should be aware that inappropriate use of fluoroquinolones could select such a strain harboring a quinolone resistance-associated alteration of DNA gyrase.

Morphology of the temporomandibular joint in skeletal class iii symmetrical and asymmetrical cases: a study by cephalometric laminography

The aetiology of asymmetric growth in the mandible is not well understood. Previous studies have indicated that the functional lateral shift of the mandible in the period of prepubertal growth may translate to a true skeletal asymmetry, exclusively in skeletal Class III malocclusion. This asymmetry develops more characteristic features during the pubertal and post-pubertal growth periods. Early correction of a functional lateral shift of the mandible is recommended. The purpose of this study was to examine the relationship between the morphology of the temporomandibular joints and asymmetry in skeletal Class III malocclusion in adult female patients. Cephalometric and laminographic findings in 36 asymmetric skeletal Class III patients with a lateral shift of mandible (group 3) were compared to those of 25 symmetric skeletal Class I patients (group 1) and the same number of symmetric skeletal Class III malocclusions (group 2). All the patients had received no orthodontic treatment. The results showed that the TMJ of the side to which the mandible shifted showed a significantly narrower and shorter shape of the condyle head, smaller superior condylar space, and steeper eminence than those of the unshifted side.

[Rupture of intrascrotal epidermoid cyst complicated by bacterial infection: a case report]

A 63-year-old male visited our hospital with the chief complaint of right scrotal pain. The right scrotum was swollen to the size of a small egg, and its skin was reddish. The mass was palpable independent of the right testis and epididymis. We diagnosed an intrascrotal abscess. The pus spontaneously issued from the scrotal mass. Sequentially, the abscess was extracted under spinal anesthesia. Membrane-like tissue assumed as the abscess wall was removed. Histologically, the abscess wall was composed of epidermal structure with epidermal keratinization, and horny material was found inside the wall. In the scrotal epidermis overlying the abscess, infiltration of neutrophils, lymphocytes, and multinucleated giant cells were observed. Anaerobic bacteria were detected in the pus of the abscess. Consequently, we diagnosed this case as rupture of an intrascrotal epidermoid cyst complicated by bacterial infection.