Podcast
Questions and Answers
What is the initial management step for a patient suspected of having peritonitis?
What is the initial management step for a patient suspected of having peritonitis?
In the case of community-acquired secondary peritonitis, which combination of antibiotics is recommended?
In the case of community-acquired secondary peritonitis, which combination of antibiotics is recommended?
Which of the following complications may arise from untreated peritonitis?
Which of the following complications may arise from untreated peritonitis?
What is the appropriate management for primary peritonitis associated with spontaneous bacterial peritonitis (SBP)?
What is the appropriate management for primary peritonitis associated with spontaneous bacterial peritonitis (SBP)?
Signup and view all the answers
Which surgical intervention is NOT typically associated with source control in peritonitis management?
Which surgical intervention is NOT typically associated with source control in peritonitis management?
Signup and view all the answers
Which peritoneal organ classification is characterized as being covered only by the parietal peritoneum on its anterior surface?
Which peritoneal organ classification is characterized as being covered only by the parietal peritoneum on its anterior surface?
Signup and view all the answers
Which type of peritonitis is characterized by an obvious source of infection due to an intra-abdominal lesion?
Which type of peritonitis is characterized by an obvious source of infection due to an intra-abdominal lesion?
Signup and view all the answers
Which clinical feature is NOT typically associated with peritonitis?
Which clinical feature is NOT typically associated with peritonitis?
Signup and view all the answers
What is the primary cause of bacterial infections in primary peritonitis?
What is the primary cause of bacterial infections in primary peritonitis?
Signup and view all the answers
Which of the following organs is classified as intraperitoneal?
Which of the following organs is classified as intraperitoneal?
Signup and view all the answers
Which symptom is associated with advanced peritonitis and can indicate sepsis?
Which symptom is associated with advanced peritonitis and can indicate sepsis?
Signup and view all the answers
What type of pathogens are commonly isolated in secondary peritonitis?
What type of pathogens are commonly isolated in secondary peritonitis?
Signup and view all the answers
Which diagnostic method is NOT routinely used for diagnosing peritonitis?
Which diagnostic method is NOT routinely used for diagnosing peritonitis?
Signup and view all the answers
Which layer of the peritoneum is attached to the abdominal wall?
Which layer of the peritoneum is attached to the abdominal wall?
Signup and view all the answers
Which organs are considered intraperitoneal?
Which organs are considered intraperitoneal?
Signup and view all the answers
The potential space between the parietal and visceral peritoneum is called the:
The potential space between the parietal and visceral peritoneum is called the:
Signup and view all the answers
What is the definition of primary peritonitis?
A. Inflammation of the peritoneum with an obvious source of infection
B. Inflammation of the peritoneum without an obvious source
C. Infection following abdominal surgery
D. Inflammation limited to the appendix
What is the definition of primary peritonitis? A. Inflammation of the peritoneum with an obvious source of infection B. Inflammation of the peritoneum without an obvious source C. Infection following abdominal surgery D. Inflammation limited to the appendix
Signup and view all the answers
Which of the following is a common cause of secondary peritonitis?
Which of the following is a common cause of secondary peritonitis?
Signup and view all the answers
Peritoneal dialysis-associated peritonitis is primarily caused by:
Peritoneal dialysis-associated peritonitis is primarily caused by:
Signup and view all the answers
Which is a feature of spontaneous bacterial peritonitis (SBP)?
Which is a feature of spontaneous bacterial peritonitis (SBP)?
Signup and view all the answers
Which organisms are most commonly implicated in Spontaneous Bacterial Peritonitis (SBP)?
Which organisms are most commonly implicated in Spontaneous Bacterial Peritonitis (SBP)?
Signup and view all the answers
Which symptom is most commonly associated with peritonitis?
Which symptom is most commonly associated with peritonitis?
Signup and view all the answers
What is the primary aetiology of PRIMARY/SBP PERITONITIS?
What is the primary aetiology of PRIMARY/SBP PERITONITIS?
Signup and view all the answers
A 32-year-old female presents with tenderness and guarding on palpation of the right iliac fossa. Ultrasound shows acute appendicitis. What is the likely diagnosis?
A 32-year-old female presents with tenderness and guarding on palpation of the right iliac fossa. Ultrasound shows acute appendicitis. What is the likely diagnosis?
Signup and view all the answers
Which of the following is a sign of generalized peritonitis?
Which of the following is a sign of generalized peritonitis?
Signup and view all the answers
Which radiological finding is suggestive of peritonitis?
Which radiological finding is suggestive of peritonitis?
Signup and view all the answers
Which test is most useful to rule out pancreatitis in a patient suspected of having peritonitis?
Which test is most useful to rule out pancreatitis in a patient suspected of having peritonitis?
Signup and view all the answers
Which is the primary initial step in managing a patient with peritonitis?
Which is the primary initial step in managing a patient with peritonitis?
Signup and view all the answers
What is the rationale for adding metronidazole in the empiric treatment of secondary peritonitis?
What is the rationale for adding metronidazole in the empiric treatment of secondary peritonitis?
Signup and view all the answers
Which antibiotic covers aerobic Gram-negative bacilli, including Pseudomonas, and also has good anaerobic cover?
Which antibiotic covers aerobic Gram-negative bacilli, including Pseudomonas, and also has good anaerobic cover?
Signup and view all the answers
Which of the following antibiotics provides anaerobic coverage?
Which of the following antibiotics provides anaerobic coverage?
Signup and view all the answers
The empiric treatment for community-acquired secondary peritonitis typically includes:
The empiric treatment for community-acquired secondary peritonitis typically includes:
Signup and view all the answers
What is the recommended empiric treatment for hospital-acquired secondary peritonitis?
What is the recommended empiric treatment for hospital-acquired secondary peritonitis?
Signup and view all the answers
Why is gentamicin added to the treatment regimen in secondary peritonitis?
Why is gentamicin added to the treatment regimen in secondary peritonitis?
Signup and view all the answers
Which of the following actions is part of the 'source control' in peritonitis management?
Which of the following actions is part of the 'source control' in peritonitis management?
Signup and view all the answers
What is the usual route of antimicrobial administration for PD-associated peritonitis?
What is the usual route of antimicrobial administration for PD-associated peritonitis?
Signup and view all the answers
What is the significance of performing an ascitic tap in suspected primary peritonitis?
What is the significance of performing an ascitic tap in suspected primary peritonitis?
Signup and view all the answers
Which antibiotic combination provides broad-spectrum coverage, including anaerobes?
Which antibiotic combination provides broad-spectrum coverage, including anaerobes?
Signup and view all the answers
Which of the following antimicrobials is a narrow-spectrum antibiotic?
Which of the following antimicrobials is a narrow-spectrum antibiotic?
Signup and view all the answers
In secondary peritonitis, the addition of gentamicin to piperacillin-tazobactam is primarily to:
In secondary peritonitis, the addition of gentamicin to piperacillin-tazobactam is primarily to:
Signup and view all the answers
Which of the following antibiotics does NOT provide anaerobic cover?
Which of the following antibiotics does NOT provide anaerobic cover?
Signup and view all the answers
Why might metronidazole be added to cefuroxime in secondary peritonitis?
Why might metronidazole be added to cefuroxime in secondary peritonitis?
Signup and view all the answers
Which is a potential complication of untreated peritonitis?
Which is a potential complication of untreated peritonitis?
Signup and view all the answers
Which of the following is a severe complication of peritonitis?
Which of the following is a severe complication of peritonitis?
Signup and view all the answers
Which of the following may result from adhesions formed due to peritonitis?
Which of the following may result from adhesions formed due to peritonitis?
Signup and view all the answers
What condition can localized abscesses due to peritonitis lead to?
What condition can localized abscesses due to peritonitis lead to?
Signup and view all the answers
Septic shock in peritonitis may present with:
Septic shock in peritonitis may present with:
Signup and view all the answers
A patient with liver cirrhosis presents with fever and abdominal pain. Ascitic fluid analysis reveals elevated neutrophils. What is the most likely diagnosis?
A patient with liver cirrhosis presents with fever and abdominal pain. Ascitic fluid analysis reveals elevated neutrophils. What is the most likely diagnosis?
Signup and view all the answers
In a patient with a perforated duodenal ulcer, which type of peritonitis is most likely?
In a patient with a perforated duodenal ulcer, which type of peritonitis is most likely?
Signup and view all the answers
A 55-year-old female on peritoneal dialysis develops abdominal pain and cloudy peritoneal fluid. Which antibiotic route is preferred?
A 55-year-old female on peritoneal dialysis develops abdominal pain and cloudy peritoneal fluid. Which antibiotic route is preferred?
Signup and view all the answers
A patient with generalized peritonitis after a bowel perforation is most likely to have:
A patient with generalized peritonitis after a bowel perforation is most likely to have:
Signup and view all the answers
Which condition is a risk factor for developing spontaneous bacterial peritonitis (SBP)?
Which condition is a risk factor for developing spontaneous bacterial peritonitis (SBP)?
Signup and view all the answers
Which imaging modality is most useful to identify free air in the abdomen due to perforation?
Which imaging modality is most useful to identify free air in the abdomen due to perforation?
Signup and view all the answers
Which antibiotic is most likely to cause nephrotoxicity and requires monitoring?
Which antibiotic is most likely to cause nephrotoxicity and requires monitoring?
Signup and view all the answers
The main goal of empiric antibiotic therapy in peritonitis is to:
The main goal of empiric antibiotic therapy in peritonitis is to:
Signup and view all the answers
An appendectomy is primarily performed as:
An appendectomy is primarily performed as:
Signup and view all the answers
Which of the following is least likely to be a cause of secondary peritonitis?
Which of the following is least likely to be a cause of secondary peritonitis?
Signup and view all the answers
Which symptom differentiates primary from secondary peritonitis?
Which symptom differentiates primary from secondary peritonitis?
Signup and view all the answers
Which lab test is essential in the evaluation of peritoneal fluid in spontaneous bacterial peritonitis (SBP)?
Which lab test is essential in the evaluation of peritoneal fluid in spontaneous bacterial peritonitis (SBP)?
Signup and view all the answers
Which statement is true regarding peritoneal lavage in peritonitis?
Which statement is true regarding peritoneal lavage in peritonitis?
Signup and view all the answers
Peritonitis can lead to ileus, which is characterized by:
Peritonitis can lead to ileus, which is characterized by:
Signup and view all the answers
Which finding is least suggestive of an acute abdomen due to peritonitis?
Which finding is least suggestive of an acute abdomen due to peritonitis?
Signup and view all the answers
What is the initial imaging study recommended for a patient with suspected acute appendicitis?
What is the initial imaging study recommended for a patient with suspected acute appendicitis?
Signup and view all the answers
In a patient with suspected primary peritonitis, which laboratory test is most essential for confirming the diagnosis?
In a patient with suspected primary peritonitis, which laboratory test is most essential for confirming the diagnosis?
Signup and view all the answers
What finding on an abdominal X-ray is a classic sign of free intraperitoneal air?
What finding on an abdominal X-ray is a classic sign of free intraperitoneal air?
Signup and view all the answers
Which of the following is a key radiological sign of a perforated viscus on an erect chest X-ray?
Which of the following is a key radiological sign of a perforated viscus on an erect chest X-ray?
Signup and view all the answers
In diagnosing peritoneal dialysis-associated peritonitis, what is the most important diagnostic test?
In diagnosing peritoneal dialysis-associated peritonitis, what is the most important diagnostic test?
Signup and view all the answers
Which of the following is the best imaging modality to evaluate suspected intra-abdominal abscesses?
Which of the following is the best imaging modality to evaluate suspected intra-abdominal abscesses?
Signup and view all the answers
What is the purpose of performing an "ascitic tap" in patients with suspected primary peritonitis?
What is the purpose of performing an "ascitic tap" in patients with suspected primary peritonitis?
Signup and view all the answers
Which laboratory finding is most commonly elevated in secondary peritonitis?
Which laboratory finding is most commonly elevated in secondary peritonitis?
Signup and view all the answers
Which laboratory test is most indicative of infection and inflammation in peritonitis?
Which laboratory test is most indicative of infection and inflammation in peritonitis?
Signup and view all the answers
Which of the following statements is true about Spontaneous Bacterial Peritonitis (SBP)?
Which of the following statements is true about Spontaneous Bacterial Peritonitis (SBP)?
Signup and view all the answers
Which diagnostic procedure is used to confirm Spontaneous Bacterial Peritonitis (SBP)?
Which diagnostic procedure is used to confirm Spontaneous Bacterial Peritonitis (SBP)?
Signup and view all the answers
In primary peritonitis, what is the primary purpose of performing an ascitic tap?
In primary peritonitis, what is the primary purpose of performing an ascitic tap?
Signup and view all the answers
Which of the following findings in peritoneal fluid analysis would suggest Spontaneous Bacterial Peritonitis (SBP)?
Which of the following findings in peritoneal fluid analysis would suggest Spontaneous Bacterial Peritonitis (SBP)?
Signup and view all the answers
Why is it crucial to exclude occult perforation in patients with suspected primary peritonitis?
Why is it crucial to exclude occult perforation in patients with suspected primary peritonitis?
Signup and view all the answers
Peritoneal dialysis (PD)-associated peritonitis is typically caused by which of the following types of organisms?
Peritoneal dialysis (PD)-associated peritonitis is typically caused by which of the following types of organisms?
Signup and view all the answers
Which of the following is an indication for removal of the PD catheter in PD-associated peritonitis?
Which of the following is an indication for removal of the PD catheter in PD-associated peritonitis?
Signup and view all the answers
Which type of infection is most commonly associated with monomicrobial peritoneal fluid culture?
Which type of infection is most commonly associated with monomicrobial peritoneal fluid culture?
Signup and view all the answers
Which of the following antibiotics is typically used for empiric therapy in primary peritonitis (SBP)?
Which of the following antibiotics is typically used for empiric therapy in primary peritonitis (SBP)?
Signup and view all the answers
What is the most common source of microorganisms in PD-associated peritonitis?
What is the most common source of microorganisms in PD-associated peritonitis?
Signup and view all the answers
Which clinical sign is most indicative of PD-associated peritonitis?
Which clinical sign is most indicative of PD-associated peritonitis?
Signup and view all the answers
What is the rationale behind using intraperitoneal antibiotics in PD-associated peritonitis?
What is the rationale behind using intraperitoneal antibiotics in PD-associated peritonitis?
Signup and view all the answers
Which of the following is a common causative organism of Spontaneous Bacterial Peritonitis (SBP)?
Which of the following is a common causative organism of Spontaneous Bacterial Peritonitis (SBP)?
Signup and view all the answers
Which of the following is a critical step in the management of Spontaneous Bacterial Peritonitis (SBP)?
Which of the following is a critical step in the management of Spontaneous Bacterial Peritonitis (SBP)?
Signup and view all the answers
Which microorganism is less commonly associated with PD-associated peritonitis?
Which microorganism is less commonly associated with PD-associated peritonitis?
Signup and view all the answers
Which imaging modality is most useful for diagnosing bowel perforation in secondary peritonitis?
Which imaging modality is most useful for diagnosing bowel perforation in secondary peritonitis?
Signup and view all the answers
What kind of fluid's presence during a diagnostic paracentesis is highly suggestive of spontaneous bacterial peritonitis (SBP)?
What kind of fluid's presence during a diagnostic paracentesis is highly suggestive of spontaneous bacterial peritonitis (SBP)?
Signup and view all the answers
A 52-year-old male with a history of cirrhosis and ascites presents with abdominal pain, fever, and tenderness. He is diagnosed with secondary peritonitis. Which empiric antibiotic regimen would you start for this patient with a community-acquired infection?
A 52-year-old male with a history of cirrhosis and ascites presents with abdominal pain, fever, and tenderness. He is diagnosed with secondary peritonitis. Which empiric antibiotic regimen would you start for this patient with a community-acquired infection?
Signup and view all the answers
A 67-year-old female develops hospital-acquired secondary peritonitis after 10 days of treatment for acute pancreatitis. She had previously been treated with ceftriaxone for a urinary tract infection. What is the most appropriate empiric therapy for this hospital-acquired infection?
A 67-year-old female develops hospital-acquired secondary peritonitis after 10 days of treatment for acute pancreatitis. She had previously been treated with ceftriaxone for a urinary tract infection. What is the most appropriate empiric therapy for this hospital-acquired infection?
Signup and view all the answers
A 59-year-old male with diabetes and recent broad-spectrum antibiotic use presents with suspected secondary peritonitis. Despite antibiotic treatment, his condition worsens, and the suspicion of a fungal infection arises. Which antifungal should be considered?
A) Caspofungin
B) Voriconazole
C) Nystatin
D) Amphotericin B
A 59-year-old male with diabetes and recent broad-spectrum antibiotic use presents with suspected secondary peritonitis. Despite antibiotic treatment, his condition worsens, and the suspicion of a fungal infection arises. Which antifungal should be considered?
A) Caspofungin B) Voriconazole C) Nystatin D) Amphotericin B
Signup and view all the answers
A 45-year-old male with a history of diverticulitis is diagnosed with secondary peritonitis and started on piperacillin-tazobactam and gentamicin. After 48 hours, cultures show Escherichia coli and Bacteroides fragilis, both sensitive to piperacillin-tazobactam. How would you adjust his therapy?
A 45-year-old male with a history of diverticulitis is diagnosed with secondary peritonitis and started on piperacillin-tazobactam and gentamicin. After 48 hours, cultures show Escherichia coli and Bacteroides fragilis, both sensitive to piperacillin-tazobactam. How would you adjust his therapy?
Signup and view all the answers
A 70-year-old male presents with secondary peritonitis following bowel surgery. Cultures grow Klebsiella pneumoniae resistant to piperacillin-tazobactam but susceptible to gentamicin. What is the next best step?
A 70-year-old male presents with secondary peritonitis following bowel surgery. Cultures grow Klebsiella pneumoniae resistant to piperacillin-tazobactam but susceptible to gentamicin. What is the next best step?
Signup and view all the answers
A 62-year-old male with liver cirrhosis and recurrent SBP presents with peritonitis. His previous cultures grew Escherichia coli resistant to ceftriaxone. What empiric antibiotics should be started?
A 62-year-old male with liver cirrhosis and recurrent SBP presents with peritonitis. His previous cultures grew Escherichia coli resistant to ceftriaxone. What empiric antibiotics should be started?
Signup and view all the answers
A 65-year-old male with a history of chronic renal failure presents with abdominal pain, fever, and tenderness. His creatinine clearance is significantly reduced. He is diagnosed with secondary peritonitis. What would be the best empiric antibiotic choice, considering his renal function?
A 65-year-old male with a history of chronic renal failure presents with abdominal pain, fever, and tenderness. His creatinine clearance is significantly reduced. He is diagnosed with secondary peritonitis. What would be the best empiric antibiotic choice, considering his renal function?
Signup and view all the answers
A 45-year-old male is diagnosed with secondary peritonitis after bowel perforation. You suspect significant anaerobic involvement based on the clinical picture. Which of the following antibiotic combinations would provide the best anaerobic coverage?
A 45-year-old male is diagnosed with secondary peritonitis after bowel perforation. You suspect significant anaerobic involvement based on the clinical picture. Which of the following antibiotic combinations would provide the best anaerobic coverage?
Signup and view all the answers
A 70-year-old male presents with abdominal pain, fever, and signs of peritonitis. He has no history of recent hospitalization and was diagnosed with secondary peritonitis, likely community-acquired. Which empiric antibiotic regimen would be most appropriate?
A 70-year-old male presents with abdominal pain, fever, and signs of peritonitis. He has no history of recent hospitalization and was diagnosed with secondary peritonitis, likely community-acquired. Which empiric antibiotic regimen would be most appropriate?
Signup and view all the answers
A 55-year-old male develops secondary peritonitis after bowel surgery and has been in the hospital for 10 days. He is now showing signs of a severe abdominal infection. Which empiric antibiotic regimen should be initiated?
A 55-year-old male develops secondary peritonitis after bowel surgery and has been in the hospital for 10 days. He is now showing signs of a severe abdominal infection. Which empiric antibiotic regimen should be initiated?
Signup and view all the answers
A 38-year-old male with a known history of penicillin allergy (anaphylaxis) presents with secondary peritonitis. What empiric antibiotic regimen would be appropriate in this situation?
A 38-year-old male with a known history of penicillin allergy (anaphylaxis) presents with secondary peritonitis. What empiric antibiotic regimen would be appropriate in this situation?
Signup and view all the answers
Study Notes
Anatomy of the Abdomen
Peritoneum
- Definition: A continuous serous membrane lining the abdominal cavity and covering the abdominal viscera.
-
Divisions:
- Parietal peritoneum: Attached to the abdominal wall.
- Visceral peritoneum: Wrapped around visceral organs.
- Peritoneal cavity: Potential space between parietal and visceral peritoneum containing a small amount of sterile lubricating fluid, allowing layers to glide easily over each other.
Organ Classification
-
Intraperitoneal Organs:
- Fully enveloped by the visceral peritoneum.
- Examples: Stomach, liver, spleen.
-
Retroperitoneal Organs:
- Covered only by the parietal peritoneum on their anterior surface.
- Examples: Esophagus, rectum, kidneys, pancreas, ascending and descending colon.
Peritonitis
Definition
- Inflammation of the peritoneum resulting in exudate that can become purulent.
-
Types:
- Localized: Example - inflamed appendix.
- Generalized: Example - perforated colon.
- Causes: Contamination of the sterile peritoneal cavity by microorganisms (bacteria, fungi) or irritating chemicals (e.g., bile, urine, gastric content, blood).
Classification
-
Primary/Spontaneous Bacterial Peritonitis (SBP)
- No obvious source of infection.
- Often seen in patients with pre-existing ascites (e.g., chronic liver disease).
- No disruption of abdominal wall and intra-abdominal organs.
- Common pathogens: Enterobacterales (E. coli, K. pneumoniae), Pseudomonas aeruginosa, S. pneumoniae, and others.
-
Secondary Peritonitis
- Secondary to intra-abdominal lesions/spillage (e.g., perforation of an organ, penetrating injury, acute pancreatitis).
- Typically polymicrobial, reflecting the flora of the diseased GI/GU tract.
- Common pathogens: Enterobacterales, Enterococci, Streptococci, Anaerobes, Candida spp.
-
Peritoneal Dialysis (PD)-Associated Peritonitis
- Entry of organisms through the PD catheter (Tenckhoff catheter).
- Common pathogens: Skin flora (S. aureus, CoNS), less commonly GI flora.
Clinical Features
-
Symptoms:
- Abdominal pain, bloating, nausea/vomiting, anorexia.
- Pain may radiate to shoulders or back and worsen on movement.
- Fever.
-
Signs:
- Features of sepsis: fever, tachycardia, hypotension, oliguria, mottled skin.
- Acute abdomen presentation: acute pain, tenderness, distension, guarding, percussion tenderness.
-
Diagnosis:
- Laboratory Tests: Routine bloods (FBC, renal profile, liver function tests, etc.), amylase, lactate, blood cultures, urine MC&S.
- Microbiology: Peritoneal fluid specimen for Gram stain and culture.
- Radiology: Abdominal X-ray, CT abdomen & pelvis, ultrasound.
Management
-
Initial:
- NPO (nothing by mouth).
- IV cannula, analgesia, IV fluids.
- May require surgical exploration.
-
Antimicrobial Therapy:
-
Secondary Peritonitis:
- Community-acquired: Cefuroxime (covers aerobic Gram-positive cocci and Enterobacterales, but lacks anaerobic cover) + Gentamicin (provides additional Gram-negative coverage) + Metronidazole (provides anaerobic coverage).
- Hospital-acquired: Piperacillin-tazobactam (covers aerobic Gram-positive cocci, Gram-negative bacilli including Pseudomonas, and has good anaerobic cover, so no need to add metronidazole) + Gentamicin (added for Gram-negative coverage in case of resistance).
-
Primary Peritonitis (SBP) or PD Peritonitis:
- SBP: IV antimicrobials.
- PD Peritonitis: Intraperitoneal (IP) route.
-
Secondary Peritonitis:
-
Source Control:
- Drainage of abscesses.
- Surgical interventions (appendectomy, bowel resection, repair of perforation).
- Laparotomy with peritoneal lavage.
Complications
- Bloodstream infection (BSI).
- Sepsis/septic shock.
- Localized abscess/collection.
- Adhesions, which may cause pain, volvulus, or intestinal obstruction.
Case Study Recap
- Example 1: 32-year-old female with acute appendicitis - Secondary localized peritonitis.
- Example 2: 45-year-old female with perforated duodenal ulcer - Diagnosed with secondary peritonitis via CT scan showing air under the diaphragm.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Test your knowledge on the anatomy of the abdomen, focusing on the peritoneum and its divisions. Explore the classifications of intraperitoneal organs and their functions within the abdominal cavity. This quiz will help reinforce your understanding of abdominal anatomical structures.