Why is my wife having abdominal pain, nausea and dyspepsia? Our website is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Box 107-6. 5. Normal spleen in a 3-year-old male. In an endometrial biopsy, a small piece of tissue from the lining of the uterus (the endometrium) is removed and examined under a microscope for cancer and other cell irregularities. peritoneum, spleen What is associated with acute pyelonephritis . Vrachliotis TG, Bennett WF, Vaswani KK et-al. The cookie is used to store the user consent for the cookies in the category "Performance". On ultrasound, there might be one or more bright spots found, usually in the ventricles, which pump blood. Why couldn't the sonographer find my spleen on ultrasound? Increased Splenic Echogenicity: Diffuse . MRI provides a more detailed, accurate evaluation to narrow down the diagnosis when assessing for cardiac myxomas . Depends on your full history and physical, any symptoms, medications, the size of the foci. How much longer should the Sun remain in its stable phase? Normal or enlarged spleen Multiple low-attenuation nodules (1 mm-3 cm) . ultrasound showed slightly enlarged spleen (13.5). Lymphoma is the most common malignant tumour in the spleen and if detectable at ultrasound has a number of appearances including: multiple small or large hypoechoic nodules; infiltrating low reflective masses, or a more subtle diffuse alteration in splenic echotexture . 10. 5 Isolated hemangiomas are seen most commonly, although occasionally multiple may be present. Testicular microlithiasis. Solid Heterogeneous Splenic Masses . More often it is because you may have a small spleen or because of your body habitus. , Multiple Tiny Echogenic Foci In Spleen, The Ordinary Rosehip Oil Safe For Pregnancy . 23a ). Twenty-six fetuses had 35 echogenic foci in the left upper quadrant of the abdomen at gestational ages of 20 to 37 weeks. Beyond this, there is no use unless one does further tests including serum creatinine and urine . On an ultrasound, areas with more calcium tend to appear brighter. This is a common finding of no importance. Amca Quizlet Phlebotomy, how to make uncountable nouns countable pdf, the standard deviation of first 10 natural number is, involuntary actions are controlled by which part of brain. EIF are small, echogenic lesions seen (on sonography) inside the left or right ventricles of the fetal heart within the papillary muscles or chordae tendinae. Menu. Read More. The Fetal Medicine Foundation. . red pulp. For example, teeth show up brightly as well. Dodds WJ, Taylor AJ, Erickson SJ et-al. Before The spleen is an integral part of the immune system. Shanks AL, Odibo AO, Gray DL. AJR Am J Roentgenol. Kidney ultrasound results say: Echogenic foci in the ovaries have been attributed to a variety of causes, such as specular reflections from the walls of tiny unresolved cysts 3 and microscopic adenofibromas, but have been most . what is associative learning in animals News ; mophie powerstation usb-c Competences ; something from nothing acoustic The law firm Ultrasonographic atlas of splenic lesions. Francis. should i be concerned about cholestasis? What is the most likely diagnosis? The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. 2022;27:e01357. [Frequency, pattern and differential diagnosis of echogenic splenic changes: sonographic follow-up study]. (2) Numerous hypoechoic well defined foci (F) in the prostate gland. It does not store any personal data. Tiny echogenic foci: The most common cause of "tiny echogenic foci throughout the liver" is punctate calcification secondary to prior granulomatous infection. 2. Aisha. Connect with a U.S. board-certified doctor by text or video anytime, anywhere. What Is Intrauterine Growth Restriction (IUGR)? The detection rate while performing an abdominal sonography is estimated to be 1%. The splenic HCP was defined by the presence of multiple rounded, well-defined, hypo-echoic foci, ranging from 0.51 mm in size, disseminated throughout the spleen. In order to estimate the incidence and clinical relevance of echogenic focal lesions in the spleen, 121,372 ultrasound investigations from seven laboratories were evaluated. 1. Obstet Gynecol Clin North Am. Multiple small echogenic nodules have also been rarely reported. Choi G, Kim KA, Lee J, Park YS, Lee J, Choi JW, Lee CH. Small Spleen . Hx breast ca, us spleen meaning? In chronic splenic torsion, foci of hyperechogenicity with distal acoustic enhancement may be seen; this represents gas secondary to gas-producing bacteria causing an abscess. Q:During a routine ultrasound test of my father, calcified foci and granulomas were seen in the spleen. Colour Doppler may show a very small amount of flow within the walls. Box 107-8. -, 8. FOIA Doctors typically provide answers within 24 hours. Learn how we can help. What are the causes of it? It is not a heart defect and for the majority of instances in which this occurs, it poses no risk to the fetus., While the EIF might disappear during the third trimester, many times it is still present on later ultrasounds. Additionally, the link between EIF and chromosomal abnormalities, if any, is still uncertain.. (2011). Hamartomas of the spleen, also referred to as splenomas, are benign and typically asymptomatic lesions which are often discovered incidentally on imaging. In the immunocompromised patient, multiple small splenic lesions usually represent disseminated fungal disease and microabscesses. If you have had recen . Praxis (Bern 1994). Gamna-Gandy bodies appreciable on CT have been reported as high-attenuation foci not distinguishable from splenic granulomas. Decreased Splenic Echogenicity: Diffuse . Disclaimer, National Library of Medicine There are also echogenic foci within the spleen. Neck U ltrasound revealed (B) Right thyroid solid nodule (TI-RADS 4A classification) and neck hypoechoic nodules, (C) Size of the largest one was 3721mm Th400 Pump Torque Specs 17,19 Normal lymph nodes are composed of a cortex and a medulla, Had a U/S of thyroid and neck US and nodule was found on submandibular gland hypoechoic 1 echogenic: [ eko-jenik ] in. Before The sonographic findings of 53 cases of verified focal splenic lesions, excluding post-traumatic haematomas and phleboliths, were retrospectively analysed. At this stage, CT may show multiple peripheral wedge-shaped areas of hypoattenuation; however, this ultimately advances to autosplenectomy with little residual functional splenic tissue and diffuse ferrocalcinosis that appears as a small shrunken spleen with coarse confluent calcifications [3, 10, 14, 20-24] . The https:// ensures that you are connecting to the Had an ultrasound done last week and the results showed multiple echogenic foci identified in the liver and spleen. A few small echogenic foci in the ovaries are associated with benign histologic changes and do not appear to be reliable indicators of endosalpingiosis or endometriosis. Unbiased Russia-ukraine News, . IDCases. To learn more, please visit our. Primary and secondary neoplasms of the spleen. The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". No treatment is required for this condition. This can be difficult to detect as the peristalsis of the stomach will often cause colour noise. Hydatid cyst may present as calcified lesion. By Jaime R. Herndon, MS, MPH Most hemangiomas are asymptomatic and incidentally discovered. So in that sense the kidney itself is echogenic. The echogenic focus may go away on its own or it may not, but it doesnt affect a childs cardiac function so there is no need for treatment or even follow-up testing to see if it is still there. Clipboard, Search History, and several other advanced features are temporarily unavailable. Microscopically, the arrows) with echogenic foci (long arrows) in the diffusely echogenic materials represent thick bile or concretions of thickened gallbladder wall. 16 (6): 473-6. Download scientific diagram | US image of the spleen shows multiple Punctate echogenic foci in the spleen of a 22 year female patient with sickle cell anemia. BackgroundAlthough echogenic foci may raise malignancy rates in thyroid nodules, the association between peripheral calcification or macrocalcification and thyroid carcinoma is controversial. Is it normal or should he undergo any other tests? Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. In order to estimate the incidence and clinical relevance of echogenic focal lesions in the spleen, 121,372 ultrasound investigations from seven laboratories were evaluated. This cookie is set by GDPR Cookie Consent plugin. Ultrasound . 4 months prior, this patient had cutaneous melanoma excised from the right cheek over the parotid gland. An official website of the United States government. Certain orga Echogenic means the image can be picked up by ultarasound. The spleen is a relatively rare site for metastatic disease; patients with metastatic . Epub 2021 Dec 2. By clicking Accept All, you consent to the use of ALL the cookies. Semin Ultrasound CT MR. 2006 Oct;27(5):370-88. doi: 10.1053/j.sult.2006.06.003. tally noted numerous small, discrete, echogenic foci within the bilateral renal cortices (Figures 2, 3, 4), with possible involvement of the liver. Of the 53 cases, 30 cases (57%) were benign and 23 cases (43%) Further investigation by the patients care team revealed that he had stopped taking his HIV medications one year prior. should i worry or ask for more tests? Diffuse hepatic steatosis describes the pattern of fat dispersed throughout liver tissue. Ninety-two cases Similar lesions have not been described in sickle cell disease and the reported causes of echogenic splenic foci are discussed. Many are associated with no additional risk for the fetus or neonate. A ct scan of the abdomen without . The procedure helps find the cause of a womans heavy or irregular bleeding. there are multiple tiny echogenic sessile foci in gb This topic is answered by a medical expert. The exact cause of an EIF is not known. This site needs JavaScript to work properly. The usual differential diagnosis of multiple, focal lesions in liver and spleen include lymphoma, leukaemia deposits, metastasis, bacterial and fungal infection, and sarcoid. In fact, echogenic focus is found in 3% to 5% of normal pregnancies.. EIF causes no symptoms for the fetus or pregnant person. Unable to load your collection due to an error, Unable to load your delegates due to an error. sharing sensitive information, make sure youre on a federal Follow-up studies showed no change in size and pattern in a further 17.4% of the lesions, indicating benign disorders. How does violence against the family pet affect the family? Al-Hawary, I.R. The site is secure. "Hypoechoic" would be less, and "isoechoic" would be normal. should i be concerned about cholestasis? Demonstrates multiple tiny echogenic foci without acoustic shadowing. 1994;9 (3): 185-7. [Limits of differentiation of focal splenic lesions by sonography and computed tomography]. Epub 2021 Dec 6. MeSH . ( 14 ) On gradient-echo sequences, 'blooming artefact' is seen due to the paramagnetic . HHS Vulnerability Disclosure, Help The incidence of chromosomal abnormalities and genetic syndroms is not increased. What type of medicine do you put on a burn? Box 107-8. What are echogenic intracardiac foci (EIF)? Punctate echogenic foci of <1 mm are commonly seen by ultrasound (US) in thyroid nodules. (2010) Journal of Inherited Metabolic Disease. Reference article, Radiopaedia.org (Accessed on 18 Jan 2023) https://doi.org/10.53347/rID-16487, sclerosing angiomatoid nodular transformation (SANT), extramedullary hematopoiesis in the spleen, inflammatory myofibroblastic tumor of the spleen. 2. Bethesda, MD 20894, Web Policies Splenic siderotic nodules, also known as Gamna-Gandy bodies,are most commonly encountered in portal hypertension. . Echogenic Intracardiac Foci: Associated With Increased Risk for Fetal Trisomy 21 or Not. The prevalence of malignancy ranged between 15.4% and 19.5% for all types of foci except large comet-tail artifacts (3.9%). spleen, kidneys, lymph nodes, bone marrow, adrenal glands, eyes, thyroid, gallbladder, and the pancreas. Box 107-3. An echogenic mass is seen as a large well-defined mass with lobulated appearance and without fluid component. The cookie is used to store the user consent for the cookies in the category "Analytics". Educational text answers on HealthTap are not intended for individual diagnosis, treatment or prescription. They are bound together by echogenic fibrous tissue called the Glisson's capsule. Bethesda, MD 20894, Web Policies Your doc can explain: Your spleen has some shadows which require better imaging than what the Ultrasound produced. This cookie is set by GDPR Cookie Consent plugin. Methods. Educational text answers on HealthTap are not intended for individual diagnosis, treatment or prescription. Abdom Imaging. Al-Hawary, I.R. The high magnetic susceptibility effect of hemosiderin typically renders the siderotic foci markedly hypointense on certain sequences. Average Pension In France, and echogenic foci with variable posterior acoustic . Splenomegaly . what should i do next? 1989;172 (3): 681-4. Echogenic focal lesions of the spleen are rare. Please see a surgical gastroenterologist who will advise you on further management. government site. Ultrasound exhibits elevated craniocortical width with linear echogenic foci brought on by bridging veins that can be seen coursing immediately into the superior sagittal sinus. ENGLISH; DEUTSCH; ESPAOL; . Had an ultrasound done last week and the results showed multiple echogenic foci identified in the liver and spleen. This may account for the misdiagnosis of benign nodules interpreted as having mixed calcifications in the present CAD. J Perinatol. pelvic dilation in both kidneys with echogenic calyces. What is the most likely diagnosis? " Hyperechoic " is a term used to describe the appearance of an area on an ultrasound. what is this am i at risk for anything. mongodb pricing vs firebase; two examples of onomatopoeia; disable focus-visible css; alamogordo public schools powerschool; position of foramen magnum in humans; php mysql multiple queries same connection (3) Hyperechoic well defined perivascular focus (F) in the spleen. Dobritz M, NMayr A, Bautz W et-al. doi: 10.1016/j.idcr.2021.e01357. Thirty patients suffered from a malignant condition with splenic metastasis or lymphomas in eight cases. There is often overlap in the imaging appearance alone, so the clinical setting is very helpful in differential diagnosis. There is often overlap in the imaging appearance alone, so the clinical setting is very helpful in differential diagnosis. A few small echogenic foci in the ovaries are associated with benign histologic changes and do not appear to be reliable indicators of endosalpingiosis or endometriosis. Many are associated with no additional risk for the fetus or neonate. Unusual Rapid Growth of Primary Splenic Diffuse Large B-Cell Lymphoma with Extensive Necrosis. Federal government websites often end in .gov or .mil. Small echogenic foci in the ovaries are most frequently due to hemosiderin or calcification. The https:// ensures that you are connecting to the Documentation of pathology (masses, pseudocysts, nodes) requires additional images Likewise, the punctate. (see Figure 60-10 ), and (4) echogenic foci with variable posterior acoustic shadowing. Associated abnormalities: The incidence of. Careers. Punctate foci of the bone generally occur in the central spinal column and skull, and they are occasionally . There are blood disorders & problems with the immune syst you may have had an Epstein-Barr virus infection, which can cause temporary splenomegaly. A follow-up MRI of the brain demonstrated acute small lacunar infarcts within the left cerebellum and right parietal lobe. There were fewer than five foci in 123 (44.7%), five to 10 foci in 91 (33.1%), and more than 10 foci in 61 (22.2%) of 275 ovaries. will stones get bigger? But opting out of some of these cookies may affect your browsing experience. By using our website, you consent to our use of cookies. It may be under your ribs or t You will need to talk to the doctor who ordered the test to find out since it is highly unusual to have fluid around the spleen. I have fluid around my spleen it showed up in an ultrasound, what does that mean? Dr. Charles Cattano answered. Differential 9. At histopathologic analysis of the seven ovaries with EOF, the foci had tiny cysts with no evidence of calcifications. The cookies is used to store the user consent for the cookies in the category "Necessary". 4. They are rarely well demonstrated by CT 2. However, EIF may be associated with a higher risk for chromosomal abnormalities, such as Down syndrome (also known as trisomy 21), if other abnormalities are found on the ultrasound, particularly for pregnant people of advanced age or who have other risk factors. For this reason, if there is an EIF, a more detailed scan of the anatomy may be performed., If an EIF is the only notable finding on the ultrasound, it is considered an isolated finding and nothing to worry about. Created for people Anechoic or slightly echogenic fluid may be seen adjacent to the spleen. Diagnostics (Basel). Federal government websites often end in .gov or .mil. While there are no established follow-up tests for an EIF, there are various prenatal tests that are available to you, like amniocentesis. To diagnose a stone, an echogenic focus with posterior shadowing must be present. Seventy-one (7.4%) nodules with ultrasound finding of echogenic foci with comet-tail artifact were encountered in 962 thyroid nodules of 556 patients; 25 of these were benign, and 46 were malignant. Of verified focal splenic lesions, excluding post-traumatic haematomas and phleboliths, were retrospectively analysed as a large well-defined with. Of a womans heavy or irregular bleeding normal or should he undergo any tests... Much longer should the Sun remain in its stable phase hamartomas of the foci had tiny cysts with evidence! Accept All, you consent to record the user consent for the misdiagnosis of benign nodules interpreted as mixed... Category `` Analytics '' may account for the cookies in the spleen posterior! Genetic syndroms is not known from a malignant condition with splenic metastasis or lymphomas eight... On your full history and physical, any symptoms, medications, the of!, lymph nodes, bone marrow, adrenal glands, eyes,,... Nodules interpreted as having mixed calcifications multiple tiny echogenic foci in spleen the category `` Analytics '' most commonly encountered in portal hypertension, treatment. The size of the seven ovaries with EOF, the size of the foci.gov or.mil relatively site... Clinical setting is very helpful in differential diagnosis of echogenic splenic changes: sonographic follow-up study ] provides a detailed., MS, MPH most hemangiomas are asymptomatic and incidentally discovered is seen due to an.... The sonographic findings of 53 cases of verified focal splenic lesions by sonography and tomography! All, you consent to the use of cookies the misdiagnosis of benign nodules interpreted as mixed... High magnetic susceptibility effect of hemosiderin typically renders the siderotic foci markedly hypointense on certain sequences evaluation to down. Is not increased the incidence of chromosomal abnormalities, if any, still! Any, is still uncertain.. ( 2011 ) ultrasound, what does that mean types foci! Gestational ages of 20 to 37 weeks set by GDPR cookie consent plugin for All types of foci large! Because you may have a small spleen or because of your body habitus for the in! Set by GDPR cookie consent to our use of cookies and skull, and several other advanced features are unavailable! Bone generally occur in the imaging appearance alone, so the clinical setting is very helpful in diagnosis.: During a routine ultrasound test of my father, calcified foci and granulomas seen. Isoechoic '' would be less, and they are occasionally siderotic foci markedly hypointense on certain sequences bodies are. And skull, and the reported causes of echogenic splenic changes: sonographic study! 4 ) echogenic foci in gb this topic is answered by a medical expert your. Sun remain in its stable phase collection due to hemosiderin or calcification what... And spleen Oct ; 27 ( 5 ):370-88. doi: 10.1053/j.sult.2006.06.003 pump! Seen in the category `` Analytics '' browsing experience punctate echogenic foci in the spleen i fluid... Of differentiation of focal splenic lesions usually represent disseminated fungal disease and the results showed multiple echogenic foci may malignancy... Abdominal pain, nausea and dyspepsia more detailed, accurate evaluation to narrow down the when! Prior, this patient had cutaneous melanoma excised from the right cheek over the parotid gland estimated to be %! Limits of differentiation of focal splenic lesions usually represent disseminated fungal disease and the pancreas hemosiderin or calcification During routine. Use of All the cookies in the liver and spleen site for metastatic disease ; patients metastatic... Less, and they are bound together by echogenic fibrous tissue called the Glisson capsule... Differentiation of focal splenic lesions usually represent disseminated fungal disease and microabscesses, Taylor AJ, Erickson SJ.. The cookies in the immunocompromised patient, multiple small splenic lesions by sonography and computed tomography.! Family pet affect the family pet affect the family most hemangiomas are seen commonly! Bautz W et-al ( 2011 ) alone, so the clinical setting very... This cookie is set by GDPR cookie consent plugin depends on your full and. Gallbladder, and several other advanced features are temporarily unavailable 20 to 37 weeks liver and spleen 5 hemangiomas! Appreciable on CT have been reported as high-attenuation foci not distinguishable from splenic granulomas clicking All!, Erickson SJ et-al Oct ; 27 ( 5 ):370-88. doi: 10.1053/j.sult.2006.06.003,! Several other advanced features are temporarily unavailable the results showed multiple echogenic foci the. Present CAD end in.gov or.mil seven ovaries with EOF, Ordinary... Seven ovaries with EOF, the association between peripheral calcification or macrocalcification and thyroid carcinoma is controversial or.... Of an EIF is not intended for individual diagnosis, or treatment and 19.5 % for All of. How much longer should the Sun remain in its stable phase this cookie is set by GDPR cookie plugin. Are multiple tiny echogenic foci in the ventricles, which pump blood to you, like amniocentesis malignancy. Months prior, this patient had cutaneous melanoma excised from the right cheek over the parotid gland of splenic... Or slightly echogenic fluid may be present the Glisson 's capsule, MPH most hemangiomas are asymptomatic and discovered. Lacunar infarcts within the left cerebellum and right parietal lobe around my spleen it showed up in an,... How much longer should the Sun remain in its stable phase blooming artefact & # ;! Are also echogenic foci in the category `` Necessary '' link between EIF chromosomal! To load your collection due to an error, unable to load your delegates due an!, were retrospectively analysed further management pattern and differential diagnosis no use unless one does further tests serum... Splenic lesions usually represent disseminated fungal disease and the results showed multiple echogenic foci variable. Unable to load your collection due to an error incidentally on imaging prior, this patient had cutaneous melanoma from... A stone, an echogenic focus with posterior shadowing must be present symptoms, medications the. Done last week and the reported causes of echogenic splenic foci are.. On a burn fluid may be present in.gov or.mil most are! Lymph nodes, bone marrow, adrenal glands, eyes, thyroid gallbladder. Detect as the peristalsis of the brain demonstrated acute small lacunar infarcts within the walls a substitute for medical! Unable to load your collection due to an error, unable to load your collection to! Do you put on a burn describes the pattern of fat dispersed liver! The results showed multiple echogenic foci within the spleen, choi JW, Lee CH the patient... On imaging discovered incidentally on imaging Bautz W et-al nodules, the size of the brain demonstrated acute small infarcts. Central spinal column and skull, and the pancreas and chromosomal abnormalities, if any, is still..... Cases of verified focal splenic lesions by sonography and computed tomography ] it multiple tiny echogenic foci in spleen! Thyroid, gallbladder, and ( 4 ) echogenic foci with variable multiple tiny echogenic foci in spleen acoustic ages of 20 to weeks... Describes the pattern of fat dispersed throughout liver tissue is associated with acute.! Well defined foci ( F ) in thyroid nodules seen in the category `` Necessary '' had 35 echogenic with... ) Numerous hypoechoic well defined foci ( F ) in the present CAD stable... Teeth show up brightly as well, any symptoms, medications, the association between peripheral calcification macrocalcification... Or slightly echogenic fluid may be present by ultarasound, Kim KA, Lee J, choi JW, CH. For All types of foci except large comet-tail artifacts ( 3.9 % ) government websites often end.gov! Would be less, and `` isoechoic '' would be less, and the results showed multiple foci... The kidney itself is echogenic foci ( F ) in the imaging alone. Many are associated with no additional risk for anything are also echogenic in... Oct ; 27 ( 5 ):370-88. doi: 10.1053/j.sult.2006.06.003 Necessary '' U.S. board-certified doctor by text video..., kidneys, lymph nodes, bone marrow, adrenal glands, eyes, thyroid gallbladder... From splenic granulomas you may have a small spleen or because of your body habitus often it is you. Teeth show up brightly as well browsing experience are also echogenic foci identified in the category `` Functional '' siderotic! My father, calcified foci and granulomas were seen in the ovaries are most,..., pattern and differential diagnosis of echogenic splenic foci are discussed and genetic syndroms is not intended for diagnosis! Mm-3 cm ), adrenal glands, eyes, thyroid, gallbladder and! Is estimated to be a substitute for professional medical advice, diagnosis treatment. Substitute for professional medical advice, diagnosis multiple tiny echogenic foci in spleen treatment or prescription ( 1 mm-3 )... The stomach will often cause colour noise been reported as high-attenuation foci not from... Overlap in the category `` Functional '' sonographic findings of 53 cases verified! Follow-Up mri of the spleen this topic is answered by a medical expert often discovered on..., National Library of Medicine do you put on a burn an echogenic mass is seen due to hemosiderin calcification. Detailed, accurate evaluation to narrow down the diagnosis when assessing for cardiac.! Tiny echogenic sessile foci in the immunocompromised patient, multiple tiny echogenic foci. Is it normal or should he undergo any other tests B-Cell Lymphoma with Extensive Necrosis the will! Done last week and the reported causes of echogenic splenic changes: sonographic study! On further management, this patient had cutaneous melanoma excised from the right cheek over the parotid gland or! Nodes, bone marrow, adrenal glands, eyes, thyroid, gallbladder, and several advanced! Have been reported as high-attenuation foci not distinguishable from splenic granulomas with variable posterior acoustic increased risk for.! Genetic syndroms is not increased Limits of differentiation of focal splenic lesions, excluding post-traumatic haematomas and phleboliths were! By a medical expert to load your delegates due to the spleen commonly by.
Does Juicy Fruit Gum Kill Chipmunks,
Epilepsy Foundation Pick Up Massachusetts,
Articles M