# Clinical Cases: Imaging Fundamentals and Modalities ## Case 1: Contrast-Induced Nephropathy ### Patient Demographics - **Age:** 72 years - **Sex:** Male ### Chief Complaint Routine follow-up for abdominal aortic aneurysm surveillance ### Presenting Symptoms The patient presents for scheduled CT angiography for surveillance of a known 4.5 cm infrarenal abdominal aortic aneurysm. He has a history of type 2 diabetes mellitus, hypertension, and mild chronic kidney disease with a baseline creatinine of 1.6 mg/dL (eGFR 42 mL/min/1.73m2). He reports no new symptoms but mentions he has been "a bit dehydrated" after recent gastrointestinal illness. ### Physical Exam Findings - **Vital Signs:** BP 148/86 mmHg, HR 78 bpm, RR 14/min, Temp 36.8C - **General:** Alert, well-appearing elderly male - **Cardiovascular:** Regular rate and rhythm, pulsatile abdominal mass palpable - **Extremities:** Palpable dorsalis pedis pulses bilaterally ### Imaging Findings and Interpretation **Pre-procedure Assessment:** Laboratory values obtained reveal creatinine of 1.8 mg/dL (elevated from baseline), eGFR 38 mL/min/1.73m2. The patient's recent dehydration and underlying diabetic nephropathy place him at increased risk for contrast-induced nephropathy. **Risk Stratification:** Using the Mehran Risk Score for contrast-induced nephropathy: - Hypotension: 0 points - IABP: 0 points - CHF: 0 points - Age >75: 0 points - Anemia: 0 points - Diabetes: 3 points - Contrast volume (estimated 100mL): 1 point - eGFR 38: 4 points - **Total: 8 points (moderate risk, approximately 14% risk of CIN)** **Management Decision:** Given the moderate risk profile and non-urgent indication, the procedure is postponed. The patient is instructed to ensure adequate oral hydration for 48 hours. Pre-hydration protocol with intravenous normal saline (1 mL/kg/hr for 6-12 hours before and after procedure) is planned. Metformin is held for 48 hours post-procedure due to risk of lactic acidosis if acute kidney injury develops. ### Diagnosis High-risk patient for contrast-induced nephropathy requiring pre-procedural optimization ### Management 1. Postpone non-urgent CT angiography for 48-72 hours 2. Ensure adequate oral hydration 3. Administer IV normal saline 1 mL/kg/hr starting 6 hours before and continuing 6-12 hours after contrast administration 4. Use lowest necessary contrast volume with iso-osmolar or low-osmolar contrast agent 5. Hold metformin for 48 hours post-procedure 6. Repeat creatinine 48-72 hours post-procedure to assess for nephropathy ### Radiological Image ![CT Angiography of Abdominal Aorta](case_01_image.jpg) **Image Description:** CT angiography demonstrating an infrarenal abdominal aortic aneurysm with mural thrombus. This type of contrast-enhanced study requires careful consideration of renal function and contrast-induced nephropathy risk. **Source:** Wikimedia Commons - "Abdominal aortic aneurysm" by James Heilman, MD **URL:** https://commons.wikimedia.org/wiki/File:Aneurysem.png **License:** Creative Commons Attribution-Share Alike 3.0 Unported --- ## Case 2: MRI Safety - Ferromagnetic Implant Screening ### Patient Demographics - **Age:** 58 years - **Sex:** Female ### Chief Complaint Progressive low back pain with radiculopathy, referred for lumbar spine MRI ### Presenting Symptoms The patient reports 6 weeks of progressively worsening low back pain radiating down the left posterior thigh to the calf. She describes numbness in the lateral foot and weakness with toe walking. Medical history includes coronary artery disease with a drug-eluting stent placed 3 years ago and a pacemaker implanted 8 years ago for sick sinus syndrome. ### Physical Exam Findings - **Vital Signs:** BP 132/78 mmHg, HR 62 bpm (paced rhythm) - **Neurological:** Decreased sensation in L5-S1 dermatomal distribution on left, weakness of left ankle plantarflexion (4/5), diminished left ankle reflex - **Spine:** Tenderness over lower lumbar spinous processes, positive straight leg raise at 45 degrees on left ### Imaging Findings and Interpretation **MRI Safety Screening:** The patient's pacemaker implant card is reviewed. The device is a St. Jude Medical Accent PM2112 implanted in 2016 - this is NOT an MRI-conditional device. The manufacturer documentation indicates the device is MRI unsafe due to the following risks: - Heating of leads causing tissue damage - Induced currents causing inappropriate pacing or inhibition - Reed switch activation causing asynchronous pacing - Device movement or dislodgement - Permanent device damage **Alternative Imaging Decision:** Given the absolute contraindication to MRI, CT myelography is recommended as an alternative to evaluate the lumbar nerve roots and detect disc herniation or stenosis. **CT Myelogram Findings:** Following intrathecal injection of iodinated contrast, CT imaging demonstrates: - Large left posterolateral disc herniation at L5-S1 - Compression of the traversing left S1 nerve root - Moderate central canal stenosis at this level - No evidence of cauda equina compression ### Diagnosis L5-S1 disc herniation with S1 radiculopathy; MRI contraindicated due to non-MRI-conditional pacemaker ### Management 1. Conservative management with physical therapy and oral analgesics initially 2. Epidural steroid injection under fluoroscopic guidance if symptoms persist 3. Surgical consultation if progressive neurological deficit or failed conservative management 4. Discussion with electrophysiology regarding upgrade to MRI-conditional pacemaker at next device change if MRI surveillance will be needed ### Radiological Image ![CT Myelogram](case_02_image.jpg) **Image Description:** CT myelogram demonstrating contrast within the thecal sac, which outlines the nerve roots and can demonstrate compression from disc herniation. This modality serves as an alternative to MRI when MRI is contraindicated. **Source:** Wikimedia Commons - "CT myelogram" **URL:** https://commons.wikimedia.org/wiki/File:Myelogram_showing_cord_compression.jpg **License:** Creative Commons Attribution-Share Alike 3.0 Unported --- ## Case 3: Radiation Safety - Pediatric Imaging Considerations ### Patient Demographics - **Age:** 6 years - **Sex:** Male ### Chief Complaint Right lower quadrant abdominal pain ### Presenting Symptoms The child presents with 18 hours of periumbilical pain that has migrated to the right lower quadrant. He has had one episode of vomiting and decreased appetite. His mother reports he has been walking hunched over and is reluctant to jump or climb stairs. ### Physical Exam Findings - **Vital Signs:** Temp 38.2C, HR 110 bpm, RR 22/min - **Abdomen:** Moderate tenderness in the right lower quadrant, voluntary guarding, positive Rovsing sign, mild rebound tenderness - **General:** Child appears uncomfortable but not toxic ### Imaging Findings and Interpretation **Imaging Selection Rationale:** Following ALARA principles and Image Gently guidelines, ultrasound is selected as the first-line imaging modality for this pediatric patient with suspected appendicitis because: - Avoids ionizing radiation exposure - High sensitivity (88%) and specificity (94%) for appendicitis in children - Can visualize alternative diagnoses - Readily available and does not require sedation **Ultrasound Findings:** Graded compression ultrasound of the right lower quadrant demonstrates: - Dilated, non-compressible appendix measuring 9 mm in diameter (abnormal >6 mm) - Target sign appearance on transverse imaging - Hyperemia of appendiceal wall on color Doppler - Echogenic periappendiceal fat stranding - Small amount of free fluid adjacent to the appendix - No appendicolith identified **Diagnosis Confidence:** The ultrasound findings are diagnostic for acute appendicitis with high confidence. CT is not needed for confirmation, thereby avoiding approximately 3-4 mSv of radiation exposure. ### Diagnosis Acute uncomplicated appendicitis diagnosed by ultrasound ### Management 1. Pediatric surgery consultation for appendectomy 2. NPO status and IV fluid resuscitation 3. IV antibiotics (ceftriaxone and metronidazole) per institutional protocol 4. Laparoscopic appendectomy performed within 24 hours 5. Histopathology confirmed acute suppurative appendicitis ### Radiological Image ![Ultrasound of Appendicitis](case_03_image.jpg) **Image Description:** Ultrasound demonstrating acute appendicitis with a dilated, non-compressible appendix displaying the target sign (concentric rings representing the layers of the inflamed appendiceal wall). This radiation-free imaging modality is preferred for pediatric patients. **Source:** Wikimedia Commons - "Acute appendicitis on ultrasound" **URL:** https://commons.wikimedia.org/wiki/File:Ultrasonography_of_appendicitis.jpg **License:** Creative Commons Attribution-Share Alike 3.0 Unported --- ## Learning Points 1. **Contrast-Induced Nephropathy Prevention:** Patients with eGFR <45 mL/min/1.73m2 require careful risk stratification. Prevention includes hydration, using minimal contrast volume, and considering alternative non-contrast imaging when possible. 2. **MRI Safety Screening:** All patients must be screened for ferromagnetic implants before MRI. Non-MRI-conditional pacemakers and ICDs are absolute contraindications. CT myelography provides an alternative for spine imaging. 3. **ALARA Principle in Pediatrics:** Children have greater radiosensitivity and longer remaining lifespan for radiation-induced effects. Ultrasound should be the first-line modality for suspected appendicitis in pediatric patients per Image Gently guidelines. 4. **Modality Selection:** Choosing the appropriate imaging modality requires balancing diagnostic accuracy, radiation exposure, contrast risks, and patient-specific factors. The right test for the right patient at the right time.