Anatomical variants Practice Questions
20 free Anatomical variants practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
During a laparoscopic cholecystectomy, a surgeon identifies an accessory bile duct draining directly into the gallbladder. This is most consistent with which anatomical variant?
- A Duct of Luschka
- B Double cystic duct
- C Accessory pancreatic duct
- D Aberrant right hepatic artery
Correct answer: Duct of Luschka
The duct of Luschka is an accessory bile duct that may drain into the gallbladder and is a known cause of postoperative bile leak. Recognition during surgery prevents complications.
A CT scan reveals a right-sided aortic arch in an asymptomatic adult. This variant most commonly results from persistence of which embryologic structure?
- A Right fourth aortic arch
- B Left fourth aortic arch
- C Right sixth aortic arch
- D Left sixth aortic arch
Correct answer: Right fourth aortic arch
A right-sided aortic arch arises from persistence of the right fourth aortic arch with regression of the left. It is often asymptomatic but may be associated with vascular rings.
An MRI shows a duplicated inferior vena cava (IVC). This finding results from persistence of which structure?
- A Left supracardinal vein
- B Left vitelline vein
- C Right vitelline vein
- D Common cardinal vein
Correct answer: Left supracardinal vein
Duplicated IVC occurs when the left supracardinal vein fails to regress. It may be discovered incidentally but is important for surgical and interventional planning.
A patient is found to have an arcuate uterus during evaluation for infertility. This variant is due to incomplete resorption of which embryologic structure?
- A Uterovaginal canal
- B Paramesonephric ducts
- C Urogenital sinus
- D Mesonephric ducts
Correct answer: Paramesonephric ducts
An arcuate uterus results from partial failure of resorption of the paramesonephric duct septum. It is generally benign and has minimal impact on fertility.
A surgeon notes that the right renal artery passes anterior to the IVC instead of posterior. This represents which vascular variant?
- A Circumaortic renal artery
- B Precaval right renal artery
- C Accessory superior renal artery
- D Inferior polar renal artery
Correct answer: Precaval right renal artery
A pre-caval right renal artery is a known variant in which the artery courses anterior to the IVC. Identifying this prevents inadvertent injury during retroperitoneal surgery.
Ultrasound reveals a retroesophageal right subclavian artery (arteria lusoria). Patients with this variant may present with which symptom?
- A Dysphagia
- B Hematuria
- C Right upper quadrant pain
- D Left arm weakness
Correct answer: Dysphagia
A retroesophageal right subclavian artery may compress the esophagus, resulting in dysphagia (dysphagia lusoria). Many individuals remain asymptomatic.
A patient undergoing MRI is found to have a horseshoe kidney. This occurs due to fusion of the kidneys at which location?
- A Upper poles
- B Lower poles
- C Mid-pole cortex
- D Renal hilum
Correct answer: Lower poles
Horseshoe kidney results from fusion of the lower poles. Ascent is blocked by the inferior mesenteric artery, leading to its characteristic lower position.
A neonate has a persistent median artery supplying the forearm. This artery is a remnant of which developmental vessel?
- A Primitive ulnar artery
- B Primitive radial artery
- C Axial artery
- D Interosseous artery
Correct answer: Axial artery
A persistent median artery is derived from the embryonic axial artery. It may predispose to carpal tunnel symptoms if enlarged.
A surgeon encounters an accessory spleen during a splenectomy. Where is the most common location for this structure?
- A Greater omentum
- B Splenic hilum
- C Pancreatic head
- D Left colic flexure
Correct answer: Splenic hilum
Accessory spleens most often occur at the splenic hilum. They are important to remove in cases like hereditary spherocytosis to prevent recurrent symptoms.
An abdominal CT reveals a retroaortic left renal vein. This variant predisposes to which condition?
- A Nutcracker syndrome
- B Thoracic outlet syndrome
- C May-Thurner syndrome
- D Pelvic congestion syndrome
Correct answer: Nutcracker syndrome
A retroaortic left renal vein may be compressed between the aorta and vertebral column, causing nutcracker-like symptoms. Awareness is crucial for renal surgery.
A patient has a tracheal bronchus arising directly from the trachea. This variant is most likely to affect which lung region?
- A Right upper lobe
- B Right middle lobe
- C Left upper lobe
- D Left lower lobe
Correct answer: Right upper lobe
A tracheal bronchus typically supplies the right upper lobe. It can predispose to recurrent infections in that region.
A patient has absence of the palmaris longus tendon bilaterally. This variant most commonly affects which action?
- A Wrist flexion
- B Thumb abduction
- C Finger extension
- D Forearm supination
Correct answer: Wrist flexion
The palmaris longus contributes modestly to wrist flexion, and its absence is usually asymptomatic. It is frequently used as a donor tendon in grafting procedures.
During pelvic surgery, the surgeon notes an obturator artery arising from the inferior epigastric artery. This is referred to as which variant?
- A Corona mortis
- B Supernumerary obturator artery
- C Accessory internal iliac artery
- D Persistent sciatic artery
Correct answer: Corona mortis
Corona mortis refers to a vascular connection between the obturator and external iliac systems. It is surgically significant due to risk of hemorrhage.
Imaging reveals a duplicated ureter on the right side. This is due to duplication of which embryologic structure?
- A Urogenital sinus
- B Metanephric blastema
- C Ureteric bud
- D Mesonephric duct
Correct answer: Ureteric bud
Duplicated ureters form from duplication of the ureteric bud. They may lead to ureteroceles or reflux depending on their insertion.
A patient is diagnosed with pectus excavatum. This chest wall variant involves abnormal development of which structure?
- A Manubrium
- B Xiphoid process
- C Costal cartilages
- D Sternal body
Correct answer: Costal cartilages
Pectus excavatum is caused by overgrowth of costal cartilages, leading to sternal depression. It may impact cardiopulmonary function in severe cases.
During carotid surgery, the surgeon encounters a high carotid bifurcation at the level of the hyoid bone. This variation affects which anatomical landmark?
- A C3–C4 vertebral level
- B Thyroid cartilage
- C Jugular foramen
- D Cricoid cartilage
Correct answer: C3–C4 vertebral level
The carotid bifurcation typically occurs at C3–C4. A high bifurcation alters surgical approach and risk to nearby nerves.
A CT scan identifies a persistent left superior vena cava (PLSVC). This venous variant most commonly drains into which structure?
- A Right atrium
- B Left atrium
- C Coronary sinus
- D Azygous vein
Correct answer: Coronary sinus
Most PLSVCs drain into the coronary sinus, which becomes enlarged. It is important to recognize for central line placement and cardiac procedures.
A patient has a cervical rib arising from C7. This variant increases risk for which condition?
- A Thoracic outlet syndrome
- B Carpal tunnel syndrome
- C Cubital tunnel syndrome
- D Popliteal artery entrapment
Correct answer: Thoracic outlet syndrome
A cervical rib may compress the brachial plexus or subclavian vessels, causing thoracic outlet symptoms. It is a clinically significant variant.
Imaging reveals a Meckel diverticulum. This anomaly results from incomplete obliteration of which structure?
- A Vitelline duct
- B Allantois
- C Urachus
- D Foregut diverticulum
Correct answer: Vitelline duct
Meckel diverticulum results from persistence of the vitelline duct. It may contain ectopic gastric tissue and cause bleeding.
A patient is found to have a bifid (split) median nerve at the wrist. This variant is most clinically associated with which condition?
- A Carpal tunnel syndrome
- B De Quervain tenosynovitis
- C Cubital tunnel syndrome
- D Trigger finger
Correct answer: Carpal tunnel syndrome
A bifid median nerve is a variant that increases risk of carpal tunnel symptoms, particularly when accompanied by a persistent median artery. Awareness prevents surgical injury.