A 36-year-old male is taken to the emergency room after jumping from a building. Bilateral fractures to the femur were stabilized at the scene by emergency medical technicians. The patient is lucid upon questioning and his vitals are stable. Pain only at his hips was elicited. Cervical exam was not performed. What is the best imaging study for this patient?

Computed tomography (CT) scan of cervical spine, hips, and lumbar area

AP and lateral radiographs of hips

Lateral radiograph (x-ray) of hips

Magnetic resonance imaging (MRI) of hips, knees, lumbar, and cervical area

Anterior-posterior (AP) and lateral radiographs of hips, knees, lumbar, and cervical area

A 45-year-old woman, suspected of having colon cancer, is advised to undergo a contrast-CT scan of the abdomen. She has no comorbidities and no significant past medical history. There is also no history of drug allergy. However, she reports that she is allergic to certain kinds of seafood. After tests confirm normal renal function, she is taken to the CT scan room where radiocontrast dye is injected intravenously and a CT scan of her abdomen is conducted. While being transferred to her ward, she develops generalized itching and urticarial rashes, with facial angioedema. She becomes dyspneic. Her pulse is 110/min, the blood pressure is 80/50 mm Hg, and the respirations are 30/min. Her upper and lower extremities are pink and warm. What is the most appropriate management of this patient?

Administer IM epinephrine 1:1,000, followed by steroids and antihistamines

Administer broad-spectrum IV antibiotics

Administer vasopressors (norepinephrine and dopamine)

Perform IV resuscitation with colloids

Obtain an arterial blood gas analysis

A 37-year-old woman presents to the Emergency Department after 8 hours of left sided flank pain that radiates to her groin and pelvic pain while urinating. Her medical history is relevant for multiple episodes of urinary tract infections, some requiring hospitalization, and intravenous antibiotics. In the hospital, her blood pressure is 125/83 mm Hg, pulse of 88/min, a respiratory rate of 28/min, and a body temperature of 36.5°C (97.7°F). On physical examination, she has left costovertebral tenderness and lower abdominal pain. Laboratory studies include a negative pregnancy test, mild azotemia, and a urinary dipstick that is positive for blood. Which of the following initial tests would be most useful in the diagnosis of this case?

Fractional excretion of sodium (FeNa+)

Contrast abdominal computed tomography

Blood urea nitrogen (BUN): serum creatinine (SCr) ratio

A 69-year-old woman presents with pain in her hip and groin. She states that the pain is present in the morning, and by the end of the day it is nearly unbearable. Her past medical history is notable for a treated episode of acute renal failure, diabetes mellitus, obesity, and hypertension. Her current medications include losartan, metformin, insulin, and ibuprofen. The patient recently started taking high doses of vitamin D as she believes that it could help her symptoms. She also states that she recently fell off the treadmill while exercising at the gym. On physical exam you note an obese woman. There is pain, decreased range of motion, and crepitus on physical exam of her right hip. The patient points to the areas that cause her pain stating that it is mostly over the groin. The patient's skin turgor reveals tenting. Radiography is ordered. Which of the following is most likely to be found on radiography?

Loss of joint space and osteophytes

Posterior displacement of the femoral head

A 37-year-old man is presented to the emergency department by paramedics after being involved in a serious 3-car collision on an interstate highway while he was driving his motorcycle. On physical examination, he is responsive only to painful stimuli and his pupils are not reactive to light. His upper extremities are involuntarily flexed with hands clenched into fists. The vital signs include temperature 36.1°C (97.0°F), blood pressure 80/60 mm Hg, and pulse 102/min. A non-contrast computed tomography (CT) scan of the head shows a massive intracerebral hemorrhage with a midline shift. Arterial blood gas (ABG) analysis shows partial pressure of carbon dioxide in arterial blood (PaCO2) of 68 mm Hg, and the patient is put on mechanical ventilation. His condition continues to decline while in the emergency department and it is suspected that this patient is brain dead. Which of the following results can be used to confirm brain death and legally remove this patient from the ventilator?

Lumbar puncture and CSF culture

Electromyography with nerve conduction studies

Imaging study selection principles for USMLE Step 2 CK: High-Yield CCS Cases Lessons

Imaging Principles - First, Do No Harm

ALARA Principle: As Low As Reasonably Achievable. Justify all exposure to ionizing radiation (CT, X-rays).
Prioritize non-ionizing modalities: Ultrasound (US) and MRI are safer first-line choices.
- - Crucial in pregnancy & pediatrics due to higher radiosensitivity.
Contrast Media Risks:
- - Iodinated (CT): Risk of Contrast-Induced Nephropathy (CIN).
- - Gadolinium (MRI): Risk of Nephrogenic Systemic Fibrosis (NSF).

⭐ Gadolinium is contraindicated in patients with an eGFR < 30 mL/min/1.73m² due to the risk of NSF.

Modality Matchup - Horses for Courses

Principle of Parsimony: Always start with the simplest, cheapest, and least invasive investigation that answers the clinical question. Prioritise non-radiation modalities (USG, MRI) where possible, especially in young patients and pregnancy.

Modality	Best For	Weakness	Clinical Pearl
X-Ray	Bone, Air, Calcification	Poor soft tissue detail	First-line for suspected fracture, pneumonia, intestinal obstruction.
USG	Fluid, Soft Tissues, Solid Organs	Operator-dependent, blocked by bone/gas	Modality of choice for gallbladder, biliary tree, obstetrics, and FAST.
CT Scan	Acute Bleed, Bone Detail, Trauma	High radiation dose	"Workhorse" for chest/abdomen/pelvis evaluation, staging cancer.
MRI	Soft Tissue (Brain, Spine, Joints)	Expensive, slow, CI in pacemakers	Unmatched detail for ligaments, cartilage, spinal cord, and brain tumours.

⭐ For suspected stroke, the first imaging is always a Non-Contrast CT (NCCT) head to rule out a hemorrhagic stroke, as thrombolysis is contraindicated in bleeds. MRI (specifically DWI) is more sensitive for an early ischemic stroke but is done after the NCCT.

Contrast Conundrums - To Dye or Not to Dye

Core Principle: Use contrast to evaluate vascularity, inflammation, infection, and tumors. Avoid in initial trauma, calculi search, or simple hemorrhage.
Iodinated Contrast (CT):
- ⚠️ Contraindications: Previous severe allergic reaction, severe renal impairment (eGFR < 30 mL/min/1.73m²), hyperthyroidism.
- CIN Prevention: Pre-hydration with IV normal saline is key.
Gadolinium Contrast (MRI):
- ⚠️ Risk: Nephrogenic Systemic Fibrosis (NSF) in patients with eGFR < 30.

⭐ Exam Favourite: For patients on Metformin, hold the drug on the day of the procedure and for 48 hours after if eGFR is < 30 or they have acute kidney injury, due to the risk of lactic acidosis.

Contrast media administration in renal impairment algorithm

Clinical Quick-Picks - Scan for the Plan

Initial vs. Best Test: Start with accessible, cost-effective options (X-ray, USG). The "best" or "most accurate" test (CT, MRI) is reserved for diagnostic dilemmas, staging, or pre-operative planning.
Radiation & Safety (ALARA Principle):
- No Ionizing Radiation: Ultrasound, MRI.
- Uses Ionizing Radiation: X-ray, CT, PET.
Contrast Considerations:
- Always check renal function (eGFR) before administering iodinated (CT) or gadolinium-based (MRI) contrast agents. Assess for prior allergic reactions.

⭐ In patients with Chronic Kidney Disease, calculate eGFR before a contrast CT. An eGFR < 30 mL/min/1.73m² is a major risk factor for Contrast-Induced Nephropathy (CIN).

High‑Yield Points - ⚡ Biggest Takeaways

X-ray is the first-line imaging for most suspected fractures and initial chest evaluation.

MRI offers superior soft tissue detail, making it best for neurological, joint, and muscle pathologies.

CT is the modality of choice for acute bleeds (head trauma), complex fractures, and is faster than MRI.

USG is key for bedside evaluation, pediatrics, and gallbladder/pelvic organs; it's radiation-free.

Use contrast to assess vascularity and inflammation; check renal function before administering.

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