NEET MDS Synopsis
CARCINOMA IN SITU
General Pathology
CARCINOMA IN SITU
Epithelial malignancy which has not yet invaded even -the local confines viz basement membrane is termed as carcinoma in situ (intra epithelial neoplasia, pre-invasive cancer)
This lesion merges morphologically with severe dysplasia
Common sites for carcinoma-in-situ :
Cervical squamous epithelium
Oropharynx
Bronchial epithelium.
Breast ducts and lobules.
Skin, in the form of Bowen's disease.
Glans penis and vulva in the form of Erythroplasia of Queyrat
Acanthosis nigricans
General Pathology
Acanthosis nigricans is a pigmented skin lesion commonly present in the axilla which is a phenotypic marker for an insulin-receptor abnormality as well as a marker for adenocarcinoma, most commonly of gastric origin.
CELL ORGANELLES
General Microbiology
CELLS ORGANELLES
Cell parts:
Mitochondrion – double MB structure responsible for cellular metabolism – powerhouse of the cell
Nucleus – controls synthetic activities and stores genetic information
Ribosome – site of mRNA attachment and amino acid assembly, protein synthesis
Endoplasmic reticulum – functions in intracellular transportation
Gogli apparatus/complex – composed of membranous sacs – involved in production of large CHO molecules & lysosomes
Lysosome – organelle contains hydrolytic enzymes necessary for intracellular digestion
Membrane bag containing digestive enzymes
Cellular food digestion – lysosome MB fuses w/ MB of food vacuole & squirts the enzymes inside. Digested food diffuses through the vacuole MB to enter the cell to be used for energy or growth. Lysosome MB keeps the cell iself from being digested
-Involved mostly in cells that like to phagocytose
-Involved in autolytic and digestive processes
-Formed when the Golgi complex packages up an especially large vesicle of digestive enzyme proteins
Phagosome
– vesicle that forms around a particle (bacterial or other) w/in the phagocyte that engulfed it
- Then separates from the cell membrane bag & fuses w/ lysozome to receive contents
- This coupling forms phagolysosomes in which digestion of the engulfed particle occurs
Microbodies:
- Contain catalase
- Bounded by a single membrane bag
- Compartments specialized for specific metabolic pathways
- Similar in function to lysosomes, but are smaller & isolate metabolic reactions involving H2O2
- Two general families:
· Peroxisomes: transfer H2 to O2, producing H2O2 – generally not found in plants
· Glyoxysomes: common in fat-storing tissues of the germinating seeds of plants
¨ Contain enzymes that convert fats to sugar to make the energy stored in the oils of the seed available
Inclusions
– transitory, non-living metabolic byproducts found in the cytoplasm of the cell
- May appear as fat droplets, CHO accumulations, or engulfed foreign matter.
Dautrey Procedure
General SurgeryDautrey Procedure
The Dautrey procedure is a surgical intervention aimed at
preventing dislocation of the temporomandibular joint (TMJ) by creating a
mechanical obstacle that restricts abnormal forward translation of the condylar
head. This technique is particularly beneficial for patients who experience
recurrent TMJ dislocations or subluxations, especially when conservative
management strategies have proven ineffective.
Indications:
The Dautrey procedure is indicated for patients with a history of
recurrent TMJ dislocations. It is particularly useful when conservative
treatments, such as physical therapy or splint therapy, have failed to
provide adequate stabilization of the joint.
Surgical Technique:
Osteotomy of the Zygomatic Arch: The procedure
begins with an osteotomy, which involves surgically cutting the
zygomatic arch, the bony structure that forms the prominence of the
cheek.
Depressing the Zygomatic Arch: After the osteotomy,
the zygomatic arch is depressed in front of the condylar head. This
depression creates a physical barrier that acts as an obstacle to the
forward movement of the condylar head during jaw opening or excessive
movement.
Stabilization: The newly positioned zygomatic arch
limits the range of motion of the condylar head, thereby reducing the
risk of dislocation during functional activities such as chewing or
speaking.
Mechanism of Action:
By altering the position of the zygomatic arch, the Dautrey
procedure effectively changes the biomechanics of the TMJ. The new
position of the zygomatic arch prevents the condylar head from
translating too far forward, which is a common cause of dislocation.
Postoperative Care:
Following the procedure, patients may require a period of recovery
and rehabilitation. This may include:
Dietary Modifications: Soft diet to minimize
stress on the TMJ during the healing process.
Pain Management: Use of analgesics to manage
postoperative discomfort.
Physical Therapy: Exercises to restore normal
function and range of motion in the jaw.
Outcomes:
The Dautrey procedure has been shown to be effective in preventing
recurrent TMJ dislocations. Patients often experience improved joint
stability and a better quality of life following the surgery. Successful
outcomes can lead to reduced pain, improved jaw function, and enhanced
overall satisfaction with treatment.
Bacterial Endocarditis
General Pathology
Bacterial endocarditis
Endocarditis is an infection of the endocardium of the heart, most often affecting the heart valves.
A. Acute endocarditis
1. Most commonly caused by Staphylococcus aureus.
2. It occurs most frequently in intravenous drug users, where it usually affects the tricuspid valve.
B. Subacute endocarditis
1. Most commonly caused by less virulent organisms, such as intraoral Streptococcus viridans that can be introduced systemically via dental procedures.
2. Pathogenesis: occurs when a thrombus or vegetation forms on a previously damaged or congenitally abnormal valve. These vegetations contain bacteria and inflammatory cells. Complications can arise if the thrombus embolizes, causing septic infarcts.
Other complications include valvular dysfunction or abscess formation.
3. Symptoms can remain hidden for months.
4. Valves affected (listed most to least common):
a. Mitral valve (most frequent).
b. Aortic valve.
c. Tricuspid (except in IV drug users, where the tricuspid valve is most often affected).
Berkson's Bias
Public Health DentistryBerkson's Bias is a type of selection bias that occurs in
case-control studies, particularly when the cases and controls are selected from
a hospital or clinical setting. It arises when the selection of cases
(individuals with the disease) and controls (individuals without the disease) is
influenced by the presence of other conditions or factors, leading to a
distortion in the association between exposure and outcome.
Key Features of Berkson's Bias
Hospital-Based Selection: Berkson's Bias typically
occurs in studies where both cases and controls are drawn from the same
hospital or clinical setting. This can lead to a situation where the
controls are not representative of the general population.
Association with Other Conditions: Individuals who are
hospitalized may have multiple health issues or risk factors that are not
present in the general population. This can create a misleading association
between the exposure being studied and the disease outcome.
Underestimation or Overestimation of Risk: Because the
controls may have different health profiles compared to the general
population, the odds ratio calculated in the study may be biased. This can
lead to either an overestimation or underestimation of the true association
between the exposure and the disease.
Example of Berkson's Bias
Consider a study investigating the relationship between smoking and lung
cancer, where both cases (lung cancer patients) and controls (patients without
lung cancer) are selected from a hospital. If the controls are patients with
other diseases that are also related to smoking (e.g., chronic obstructive
pulmonary disease), this could lead to Berkson's Bias. The controls may have a
higher prevalence of smoking than the general population, which could distort
the perceived association between smoking and lung cancer.
Implications of Berkson's Bias
Misleading Conclusions: Berkson's Bias can lead
researchers to draw incorrect conclusions about the relationship between
exposures and outcomes, which can affect public health recommendations and
clinical practices.
Generalizability Issues: Findings from studies affected
by Berkson's Bias may not be generalizable to the broader population,
limiting the applicability of the results.
Mitigating Berkson's Bias
To reduce the risk of Berkson's Bias in research, researchers can:
Select Controls from the General Population: Instead of
selecting controls from a hospital, researchers can use population-based
controls to ensure a more representative sample.
Use Multiple Control Groups: Employing different control
groups can help identify and account for potential biases.
Stratify Analyses: Stratifying analyses based on
relevant characteristics (e.g., age, sex, comorbidities) can help to control
for confounding factors.
Conduct Sensitivity Analyses: Performing sensitivity
analyses can help assess how robust the findings are to different
assumptions about the data.
Primary Bone Healing and Rigid Fixation
Oral and Maxillofacial SurgeryPrimary Bone Healing and Rigid Fixation
Primary bone healing is a process that occurs when bony
fragments are compressed against each other, allowing for direct healing without
the formation of a callus. This type of healing is characterized by the
migration of osteocytes across the fracture line and is facilitated by rigid
fixation techniques. Below is a detailed overview of the concept of primary bone
healing, the mechanisms involved, and examples of rigid fixation methods.
Concept of Compression
Compression of Bony Fragments: In primary bone healing,
the bony fragments are tightly compressed against each other. This
compression is crucial as it allows for the direct contact of the bone
surfaces, which is necessary for the healing process.
Osteocyte Migration: Under conditions of compression,
osteocytes (the bone cells responsible for maintaining bone tissue) can
migrate across the fracture line. This migration is essential for the
healing process, as it facilitates the integration of the bone fragments.
Characteristics of Primary Bone Healing
Absence of Callus Formation: Unlike secondary bone
healing, which involves the formation of a callus (a soft tissue bridge that
eventually hardens into bone), primary bone healing occurs without callus
formation. This is due to the rigid fixation that prevents movement between
the fragments.
Haversian Remodeling: The healing process in primary
bone healing involves Haversian remodeling, where the bone is remodeled
along the lines of stress. This process allows for the restoration of the
bone's structural integrity and strength.
Requirements for Primary Healing:
Absolute Immobilization: Rigid fixation must
provide sufficient stability to prevent any movement (interfragmentary
mobility) between the osseous fragments during the healing period.
Minimal Gap: There should be minimal distance (gap)
between the fragments to facilitate direct contact and healing.
Examples of Rigid Fixation in the Mandible
Lag Screws: The use of two lag screws across a fracture
provides strong compression and stability, allowing for primary bone
healing.
Bone Plates:
Reconstruction Bone Plates: These plates are
applied with at least three screws on each side of the fracture to
ensure adequate fixation and stability.
Compression Plates: A large compression plate can
be used across the fracture to maintain rigid fixation and prevent
movement.
Proper Application: When these fixation methods are
properly applied, they create a stable environment that is conducive to
primary bone healing. The rigidity of the fixation prevents interfragmentary
mobility, which is essential for the peculiar type of bone healing that
occurs without callus formation.
Osteoporosis
General Pathology
Osteoporosis
is characterized by increased porosity of the skeleton resulting from reduced bone mass. The disorder may be localized to a certain bone (s), as in disuse osteoporosis of a limb, or generalized involving the entire skeleton. Generalized osteoporosis may be primary, or secondary
Primary generalized osteoporosis
• Postmenopausal
• Senile
Secondary generalized osteoporosis
A. Endocrine disorders
• Hyperparathyroidism
• Hypo or hyperthyroidism
• Others
B. Neoplasia
• Multiple myeloma
• Carcinomatosis
C. Gastrointestinal disorders
• Malnutrition & malabsorption
• Vit D & C deficiency
• Hepatic insufficiency
D. Drugs
• Corticosteroids
• Anticoagulants
• Chemotherapy
• Alcohol
E. Miscellaneous
• osteogenesis imperfecta
• immobilization
• pulmonary disease
Senile and postmenopausal osteoporosis are the most common forms. In the fourth decade in both sexes, bone resorption begins to overrun bone deposition. Such losses generally occur in areas containing abundant cancelloues bone such as the vertebrae & femoral neck. The postmenopausal state accelerates the rate of loss; that is why females are more susceptible to osteoporosis and its complications.
Gross features
• Because of bone loss, the bony trabeculae are thinner and more widely separated than usual. This leads to obvious porosity of otherwise spongy cancellous bones
Microscopic features
• There is thinning of the trabeculae and widening of Haversian canals.
• The mineral content of the thinned bone is normal, and thus there is no alteration in the ratio of minerals to protein matrix
Etiology & Pathogenesis
• Osteoporosis involves an imbalance of bone formation, bone resorption, & regulation of osteoclast activation. It occurs when the balance tilts in favor of resorption.
• Osteoclasts (as macrophages) bear receptors (called RANK receptors) that when stimulated activate the nuclear factor (NFκB) transcriptional pathway. RANK ligand synthesized by bone stromal cells and osteoblasts activates RANK. RANK activation converts macrophages into bone-crunching osteoclasts and is therefore a major stimulus for bone resorption.
• Osteoprotegerin (OPG) is a receptor secreted by osteoblasts and stromal cells, which can bind RANK ligand and by doing so makes the ligand unavailable to activate RANK, thus limiting osteoclast bone-resorbing activity.
• Dysregulation of RANK, RANK ligand, and OPG interactions seems to be a major contributor in the pathogenesis of osteoporosis. Such dysregulation can occur for a variety of reasons, including aging and estrogen deficiency.
• Influence of age: with increasing age, osteoblasts synthetic activity of bone matrix progressively diminished in the face of fully active osteoclasts.
• The hypoestrogenic effects: the decline in estrogen levels associated with menopause correlates with an annual decline of as much as 2% of cortical bone and 9% of cancellous bone. The hypoestrogenic effects are attributable in part to augmented cytokine production (especially interleukin-1 and TNF). These translate into increased RANK-RANK ligand activity and diminished OPG.
• Physical activity: reduced physical activity increases bone loss. This effect is obvious in an immobilized limb, but also occurs diffusely with decreased physical activity in older individuals.
• Genetic factors: these influence vitamin D receptors efficiency, calcium uptake, or PTH synthesis and responses.
• Calcium nutritional insufficiency: the majority of adolescent girls (but not boys) have insufficient dietary intake of calcium. As a result, they do not achieve the maximal peak bone mass, and are therefore likely to develop clinically significant osteoporosis at an earlier age.
• Secondary causes of osteoporosis: these include prolonged glucocorticoid therapy (increases bone resorption and reduce bone synthesis.)
The clinical outcome of osteoporosis depends on which bones are involved. Thoracic and lumbar vertebral fractures are extremely common, and produce loss of height and various deformities, including kyphoscoliosis that can compromise respiratory function. Pulmonary embolism and pneumonia are common complications of fractures of the femoral neck, pelvis, or spine.