Anatomical Variations and Anomalies Practice Questions

Q: Which muscle is most commonly affected by congenital absence?

Pectoralis major. **Explanation:** The **Pectoralis major** is the most common muscle in the human body to be congenitally absent. This anomaly can occur as an isolated finding or as part of a larger clinical entity known as **Poland Syndrome**. 1. **Why Pectoralis Major is Correct:** Congenital absence of the pectoralis major (specifically the sternocostal head) is a classic anatomical variation. In Poland Syndrome, this absence is typically unilateral and associated with ipsilateral symbrachydactyly (short, webbed fingers), rib anomalies, and hypoplasia of the breast or nipple. It is believed to result from a vascular disruption during embryonic development (specifically the subclavian artery supply). 2. **Why Other Options are Incorrect:** * **Semimembranosus, Teres minor, and Gluteus maximus:** While anatomical variations in size or attachment points can occur in these muscles, their complete congenital absence is extremely rare and does not represent a standard high-yield clinical pattern in medical literature or embryology. **Clinical Pearls for NEET-PG:** * **Poland Syndrome Triad:** Unilateral absence of Pectoralis major + Chest wall depression + Hand anomalies (Symbrachydactyly). * **Palmaris Longus:** Often cited as the most common "missing" muscle in terms of phylogenetic regression (absent in ~15% of the population), but **Pectoralis major** remains the standard answer for "congenital absence" in a clinical/pathological context. * **Other commonly absent muscles:** Plantaris, Pyramidalis, and Psoas minor.

Q: Hemivertebra is a defect of which part of the vertebra?

Body. **Explanation:** **Hemivertebra** is a congenital spinal anomaly where only one side of the vertebral body develops. This occurs due to the **failure of one of the two lateral chondrification centers** of the vertebral body to form or fuse during embryonic development (around the 6th week of gestation). * **Why Option A is Correct:** The vertebral body (centrum) develops from two primary ossification centers. If one center fails to develop, only half of the body forms, resulting in a wedge-shaped vertebra. This is the most common cause of congenital scoliosis, as the asymmetrical growth leads to lateral curvature of the spine. * **Why Other Options are Incorrect:** * **Options B & C (Transverse process and Spine):** These are parts of the vertebral arch. While they may be secondary victims of the deformity, their primary development is not the cause of a hemivertebra. * **Option D (Posterior vertebral arches):** Defects in the fusion of the posterior arches lead to **Spina Bifida**, not hemivertebra. The arches develop from separate primary ossification centers located in each half of the neural arch. **High-Yield Clinical Pearls for NEET-PG:** 1. **Congenital Scoliosis:** Hemivertebra is the most frequent cause of structural congenital scoliosis. 2. **VACTERL Association:** Hemivertebrae are often associated with other anomalies (Vertebral, Anal, Cardiac, Tracheo-Esophageal, Renal, and Limb). 3. **Butterfly Vertebra:** Occurs when both lateral chondrification centers fail to fuse in the midline, leaving a central cleft. 4. **Ossification Centers:** A typical vertebra has **3 primary centers** (1 for the body, 2 for the arches) and **5 secondary centers** (appearing at puberty).

Q: Which of the following is NOT a component of left isomerism?

Duplication of gallbladder. **Explanation:** **Heterotaxy syndrome** refers to the abnormal arrangement of internal organs across the left-right axis. It is broadly classified into **Left Isomerism** (bilateral left-sidedness) and **Right Isomerism** (bilateral right-sidedness). **Why Option D is Correct:** **Duplication of the gallbladder** is a rare congenital biliary anomaly but is **not** a defining feature of left isomerism. In left isomerism, the gallbladder is more typically characterized by its position (often midline or left-sided) or its complete absence (**agenesis**), rather than duplication. **Analysis of Incorrect Options:** * **A. Polysplenia:** This is the hallmark of left isomerism. Instead of one single spleen, multiple small splenic masses are present on both sides of the dorsal mesogastrium. * **B. Midline Liver:** In isomerism, the normal asymmetry of the liver is lost. The liver often appears symmetric and occupies a central/midline position in the upper abdomen. * **C. Left-sided IVC:** Left isomerism is frequently associated with an interrupted IVC with azygos continuation. When the IVC is present, it is often found on the left side or in an abnormal position relative to the aorta. **High-Yield NEET-PG Pearls:** 1. **Left Isomerism (Polysplenia Syndrome):** Associated with bilateral two-lobed lungs (bilateral hyparterial bronchi), bilateral pulmonary atria, and interrupted IVC. 2. **Right Isomerism (Asplenia Syndrome):** Associated with bilateral three-lobed lungs (bilateral eparterial bronchi), bilateral systemic atria, midline liver, and **absent spleen**. 3. **Mnemonic:** **L**eft = **L**ess (fewer lung lobes, fewer cardiac conduction issues compared to right isomerism). 4. **Cardiac Defects:** Left isomerism is generally associated with less severe cardiac anomalies than right isomerism, though heart blocks are common.

Q: Main-Gruber connections are:

Median and ulnar nerve. ### Explanation **Correct Answer: D. Median and ulnar nerve** **Understanding Martin-Gruber Anastomosis (MGA)** The Martin-Gruber connection (or anastomosis) is a common anatomical variation in the **forearm** where motor nerve fibers cross over from the **median nerve** (or its branch, the anterior interosseous nerve) to the **ulnar nerve** [1]. * **Mechanism:** These crossover fibers eventually join the ulnar nerve to innervate intrinsic hand muscles, most commonly the first dorsal interosseous, adductor pollicis, and abductor digiti minimi. * **Prevalence:** It is found in approximately 15–30% of the population and is often bilateral. **Analysis of Incorrect Options:** * **Option A & B (Axillary nerve involvement):** The axillary nerve is a branch of the posterior cord that terminates near the shoulder (deltoid/teres minor). It does not have established communicating branches with the median or radial nerves in the forearm. * **Option C (Radial and ulnar nerve):** While both nerves supply the hand, there is no standard anatomical communication between them in the forearm similar to the Martin-Gruber connection. **Clinical Pearls for NEET-PG:** 1. **Electrodiagnostic Significance:** MGA is a classic "trap" in Nerve Conduction Studies (NCS). It can mimic ulnar neuropathy or Carpal Tunnel Syndrome because a stimulus at the elbow (median nerve) produces a larger muscle response in the hand than a stimulus at the wrist [1]. 2. **Riche-Cannieu Communication:** This is a similar connection but occurs in the **palm** (hand), where the recurrent branch of the median nerve communicates with the deep branch of the ulnar nerve [1]. 3. **Marinacci Communication:** Often called a "Reverse Martin-Gruber," this is a rare crossover from the ulnar nerve to the median nerve in the forearm. 4. **Berrettini Communication:** A purely sensory communication between the ulnar and median digital nerves in the palm.

Q: An absent kidney is found in approximately what proportion of individuals?

1 in 1400 individuals. The condition described is **Unilateral Renal Agenesis (URA)**, which occurs when one kidney fails to develop due to the failure of the ureteric bud to contact or induce the metanephric blastema during embryogenesis. 1. **Why Option C is Correct:** Large-scale autopsy and radiological studies indicate that unilateral renal agenesis occurs in approximately **1 in 1,100 to 1 in 1,500 births**, making **1 in 1,400** the most accurate statistical representation among the choices. It is more common in males and typically affects the left side. 2. **Analysis of Incorrect Options:** * **Option A (1 in 200):** This is too frequent. However, it is the approximate incidence of **Horseshoe Kidney**, the most common fusion anomaly. * **Option B (1 in 700):** This frequency is often associated with Polycystic Kidney Disease (ADPKD) or certain cleft lip/palate statistics, but it is too high for renal agenesis. * **Option D (1 in 5000):** This is the approximate incidence of **Bilateral Renal Agenesis** (Potter’s Syndrome), which is incompatible with life and much rarer than the unilateral form. **High-Yield NEET-PG Pearls:** * **Compensatory Hypertrophy:** In URA, the solitary kidney undergoes hypertrophy to maintain normal renal function. * **Associated Anomalies:** In females, URA is highly associated with Mullerian duct anomalies (e.g., **Mayer-Rokitansky-Küster-Hauser syndrome**). In males, it may be associated with seminal vesicle agenesis. * **Potter’s Sequence:** Caused by Bilateral Renal Agenesis leading to oligohydramnios, pulmonary hypoplasia, and flattened facies. * **Embryology:** The kidney develops from the **Metanephros** (permanent kidney), while the ureter, pelvis, and calyces develop from the **Ureteric Bud**.

Q: Wormian bones are seen in all of the following conditions EXCEPT:

Turner syndrome. **Explanation:** **Wormian bones** (also known as sutural bones) are small, irregular accessory ossicles found within the cranial sutures, most commonly in the lambdoid suture. Their presence is often associated with conditions that delay the ossification of the skull or involve metabolic bone disturbances. **Why Turner Syndrome is the Correct Answer:** Turner syndrome (45, XO) is characterized by skeletal abnormalities such as a short fourth metacarpal, cubitus valgus, and osteoporosis, but it is **not** typically associated with the formation of Wormian bones. Therefore, it is the "except" in this list. **Analysis of Incorrect Options (Conditions where Wormian bones ARE seen):** * **Hypothyroidism (Cretinism):** Delayed skeletal maturation and delayed closure of fontanelles lead to the formation of these accessory bones. * **Down’s Syndrome:** Chromosomal abnormalities in Trisomy 21 often result in delayed cranial vault ossification, making Wormian bones a common finding. * **Osteogenesis Imperfecta:** This is a classic association [1]. Due to defective Type I collagen synthesis, the skull remains thin and poorly mineralized, leading to numerous "mosaic" Wormian bones. **High-Yield Clinical Pearls for NEET-PG:** To remember the causes of Wormian bones, use the mnemonic **"PORK CHOPS"**: * **P:** Pyknodysostosis * **O:** Osteogenesis imperfecta * **R:** Rickets * **K:** Kinky Hair Syndrome (Menkes) * **C:** Cleidocranial dysplasia (High-yield: most numerous Wormian bones) [1] * **H:** Hypothyroidism / Hypophosphatasia * **O:** One too many chromosomes (Down’s syndrome) * **P:** Pachydermoperiostosis * **S:** Sutural syndrome (Apert syndrome)

Q: The characteristic triad of Klippel-Feil syndrome includes all of the following, except?

Elevated scapula. **Explanation:** **Klippel-Feil Syndrome (KFS)** is a rare skeletal disorder characterized by the congenital fusion of two or more cervical vertebrae. This occurs due to the failure of normal segmentation of cervical somites during the 3rd to 8th week of gestation. **Why "Elevated Scapula" is the correct answer:** The classic **clinical triad** of Klippel-Feil syndrome consists of: 1. **Short neck** 2. **Low posterior hairline** 3. **Limited neck motion** (due to fused vertebrae) While **Sprengel’s deformity** (congenital elevation of the scapula) is the most common associated anomaly (found in about 25-35% of cases), it is **not** part of the defining diagnostic triad. Therefore, it is the "except" in this question. **Analysis of Incorrect Options:** * **Short neck (A):** A direct result of the reduced number of functional intervertebral spaces due to fusion. * **Low hairline (B):** A classic phenotypic feature caused by the shortened cervical spine. * **Limited neck movements (C):** The hallmark functional deficit resulting from synostosis (fusion) of the cervical vertebrae. **NEET-PG High-Yield Pearls:** * **Associated Anomalies:** Scoliosis, renal agenesis, deafness, and Sprengel’s deformity. * **Radiology:** Lateral X-ray of the cervical spine is the gold standard for diagnosis (shows "block vertebrae"). * **Genetic Association:** Often linked to mutations in *GDF6* or *GDF3* genes. * **Wildervanck Syndrome:** A variant of KFS associated with Duane syndrome (eye movement disorder) and sensorineural deafness.

Q: Which of the following conditions is not hereditary?

Regional odontodysplasia. ### Explanation The correct answer is **Regional Odontodysplasia (ROD)**. **1. Why Regional Odontodysplasia is the correct answer:** Unlike the other options, Regional Odontodysplasia (also known as **"Ghost Teeth"**) is a non-hereditary developmental anomaly. Its exact etiology is unknown, though it is hypothesized to result from local vascular defects, trauma, or latent viral infections. It typically affects a localized quadrant (usually the maxilla) and involves both ectodermal (enamel) and mesodermal (dentin/pulp) components. Radiographically, teeth show thin layers of enamel and dentin with large pulp chambers, giving them a characteristic "ghost-like" appearance. **2. Why the other options are incorrect:** * **Amelogenesis Imperfecta (A):** A group of **hereditary** disorders (Autosomal Dominant, Recessive, or X-linked) that specifically affect enamel formation without systemic involvement. * **Cleidocranial Dysostosis (B):** An **Autosomal Dominant** skeletal condition caused by a mutation in the *RUNX2* gene [1]. It is characterized by supernumerary teeth, delayed eruption, and absent/hypoplastic clavicles [1]. * **Dentinogenesis Imperfecta (D):** A **hereditary** defect of dentin (Autosomal Dominant) often associated with the *DSPP* gene. It results in opalescent teeth and premature closure of pulp chambers. **3. High-Yield Clinical Pearls for NEET-PG:** * **Ghost Teeth:** Pathognomonic radiographic sign for Regional Odontodysplasia. * **Shell Teeth:** Often seen in Dentinogenesis Imperfecta Type III (Brandywine type). * **Cleidocranial Dysostosis:** Look for keywords like "supernumerary teeth," "prolonged retention of deciduous teeth," and "ability to approximate shoulders" [1]. * **Dentinogenesis Imperfecta Type I** is always associated with **Osteogenesis Imperfecta** (Blue sclera).

Question 1

Which muscle is most commonly affected by congenital absence?

Accepted Answer

Pectoralis major

Answer

Semimembranosus

Answer

Teres minor

Answer

Gluteus maximus

Question 2

Hemivertebra is a defect of which part of the vertebra?

Accepted Answer

Body

Answer

Transverse process

Answer

Spine

Answer

Posterior vertebral arches

Question 3

Which of the following is NOT a component of left isomerism?

Accepted Answer

Duplication of gallbladder

Answer

Polysplenia

Answer

Midline liver

Answer

Left sided Inferior Vena Cava

Question 4

Main-Gruber connections are:

Accepted Answer

Median and ulnar nerve

Answer

Median and axillary nerve

Answer

Axillary and radial nerves

Answer

Radial and ulnar nerve

Question 5

Which of the following represents the commonest variation in the arteries arising from the arch of the aorta?

Accepted Answer

Left common carotid artery arising from the brachiocephalic trunk

Answer

Absence of brachiocephalic trunk

Answer

Left vertebral artery arising from the arch

Answer

Presence of retroesophageal subclavian artery

Question 6

An absent kidney is found in approximately what proportion of individuals?

Accepted Answer

1 in 1400 individuals

Answer

1 in 200 individuals

Answer

1 in 700 individuals

Answer

1 in 5000 individuals

Question 7

Wormian bones are seen in all of the following conditions EXCEPT:

Accepted Answer

Turner syndrome

Answer

Hypothyroidism

Answer

Down's syndrome

Answer

Osteogenesis imperfecta

Question 8

The characteristic triad of Klippel-Feil syndrome includes all of the following, except?

Accepted Answer

Elevated scapula

Answer

Short neck

Answer

Low hairline

Answer

Limited neck movements

Question 9

What does 'Unicollis bicornis' mean?

Accepted Answer

Two uterine cavities with one cervix

Answer

Single vagina with a double uterus

Answer

Incomplete uterine septum

Answer

Double uterus and double cervix

Question 10

Which of the following conditions is not hereditary?

Accepted Answer

Regional odontodysplasia

Answer

Amelogenesis imperfecta

Answer

Cleidocranial dysostosis

Answer

Dentinogenesis imperfecta

Anatomical Variations and Anomalies — MCQs

Anatomical Variations and Anomalies — MCQs

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