Organ Variation Flashcards
How can the spleen vary?
Lobulation
Accessory spleen
Wandering spleen
Polysplenia
How does the spleen develop?
Develops in dorsal mesogastrium in week 5
Stomach rotates and carries spleen from midline to left
Rotation of mesogastrium forms splenorenal (lienorenal) ligament
What structure does the foetal spleen have?
Lobulated
What can remnants of the foetal spleen show as in adults?
Clefts
Grooves
What pathology can remnants of the foetal spleen resemble?
Splenic lacerations
If lobulations persist on the medial border of the spleen, where can they extend to?
Upper pole of left kidney
What is the typical size for an accessory spleen?
1-3cm
Where do accessory spleens develop?
In early peritoneal folds
Where are the most common sites for accessory spleens?
Hilum of spleen
Near tail of pancreas
Where else can an accessory spleen be found?
Near splenic vessels In tail of pancreas In gastrosplenic or lienorenal ligament Wall of stomach/bowel In mesentery Pelvis/scrotum
What is the prevalence of accessory spleens?
10%
What does an accessory spleen resemble on CT?
Lymph node
What is a potential benefit of an accessory spleen?
Valuable source of splenic tissue for patients with a ruptured primary spleen
What is the prevalence of a wandering/ectopic spleen?
0.5%
What is the aetiology of a wandering spleen?
Failures in gastrosplenic and lienorenal ligament development:
- Abnormally long splenic mesentery
- Abnormally mobile spleen
In what individuals is a wandering spleen most common?
Children
Women aged 20-40 years
How does a wandering spleen present?
Asymptomatic Splenic torsion: - Pain (variable) - May spontaneously de-twist Acute torsion: - Infarction - Capsule stretching
What did a case study by Gayar et al., (2001) show in relation to a wandering spleen?
26 year old female with abdominal pain: - Spleen in mid-abdomen 4 years later: - Spleen now in lower pelvis - Spleen adjacent to bladder and uterus
What laterality disorders can lungs display?
Left isomerism:
- Both lungs have the appearance and structure of an anatomically left lung
Right isomerism:
- Both lungs have the appearance and structure of an anatomically right lung
Within the lungs, what are lobar variations important in identification of?
Bronchopulmonary segments
What other general lung variations can be seen?
Accessory tissues
Variant fissures
In a study by Prakash et al., (2010), what were the findings regarding the transverse fissure?
Absent in 7.1%
Incomplete in 50%
In a study by Prakash et al., (2010), what were the findings regarding the oblique fissure?
Right: - Absent in 7.1% - Incomplete in 39.3% Left: - Absent in 10.7% - Incomplete in 35.7%
What did 1 of the 29 individuals in the cadaver study by Prakash et al., (2010) have?
A single lung filling entire thoracic cavity
What other features were seen as variants in the Prakash et al., (2010) study?
Accessory lobe in 27.2%
Supernumerary fissures in 35%
What variations did Eroje and Onyije, (2011) note regarding lobar variations?
Right lung:
- One with incomplete horizontal fissure
- One with absent horizontal fissure
What variation did Nene et al., (2010) note regarding lobar variations?
Left lung with an accessory fissure
How did Gonlugar et al., (2005) describe the embryonic origin of tracheobronchial tree variations?
Anomalies result in lung buds develop at atypical sites or to an inappropriate number:
- Failure of regression?
- Migration of additional mesenchyme?
How many bronchoscopies did Gonlugar et al., (2005) review?
2550
How many of the bronchoscopies examined by Gonlugar et al., (2005) displayed major tracheobronchial tree variations?
2.6% (67 patients)
What was the most common major tracheobronchial tree variation found by Gonlugar et al., (2005)?
Bifurcate pattern in right upper lobe:
- In 32 out of the 67 patients with variants (47.8%)
Where was the most common site for variation in the lungs noted by Gonlugar et al., (2005)?
Right upper lobe:
- 71.6%
In who are the variants noted by Gonlugar et al., (2005) most common?
In men:
- For all variants except one
What are some examples of right sided variations noted by Gonlugar et al., (2005)?
Tracheal (pre-eparterial) bronchus
Right upper lobe segments
Post-eparterial bronchus
Accessory cardiac bronchus
When does the liver primordium appear in utero?
In the middle of the 3rd week
What is the liver bud?
An outgrowth of endodermal epithelium in the distal foregut
What does the liver bud grow into? What does this structure also contribute to?
Septum transversum:
- A mesodermal plate between pericardial cavity and stalk of yolk sac
- Also contributes to diaphragm
How does the bile duct form?
As the liver bud continues to penetrate the septum transversum, the connection between the liver bud (hepatic diverticulum) and duodenum narrows
What forms the gallbladder and cystic duct?
A small ventral outgrowth from the bile duct
Where does the liver lie in situs inversus?
On the left
In isomerism (situs ambiguus), where do the liver and gallbladder lie?
Midline
What are the type 1 liver variations?
Defective:
- Agenesis
- Aplasia
- Hypoplasia
What are the type 2 liver variations?
Excessive:
- Accessory lobes
- Ectopic tissue
Is total liver agenesis serious?
Yes
Is partial liver agenesis serious?
Usually not
How does partial liver agenesis present?
Asymptomatic
Usually incidentally found during:
- Surgery
- Autopsy
What studies describe hypoplasia or agenesis of the left lobe of the liver?
Prithishkumar and Kanakasabapathy, 2010 (agenesis)
Belton and VanZandt, 1983 (total congenital absence)
What studies describe hypoplasia or agenesis of the right lobe of the liver?
Radin et al., 1987 (agenesis)
Inoue et al., 1997 (hypoplasia)
Describe the findings of the Belton and VanZandt, (1983) study?
70 year old female:
- Total absence of left lobe on laparotomy
43 year old male:
- Thought to have hepatomegaly on examination
- CT showed a transverse stomach (mimicked hepatomegaly) and no liver to left of gallbladder fossa
What were the variations noted in the 68 year old females cadaver in the case study by Prithishjumar and Kanakasabapathy, (2010)?
Total agenesis of left lobe up to falciform ligament 5 separate nodules around porta hepatis: - One attached to gallbladder - One attached to falciform ligament Right lobe: - Abnormal shape - Poorly defined inferior border Caudate lobe hypertrophy Thick connective tissue band to left of falciform ligament
What did histological analysis of the thick connective tissue band in the cadaver in the Prithishjumar and Kanakasabapathy, (2010) case study find?
Dense connective tissue
Small tubes
A few blood vessels
What did Prithishjumar and Kanakasabapathy, (2010) conclude the thick connective tissue band was? What did they determine this had caused?
A connective tissue remnant of septum transversum:
- Stopped development of portion of hepatic epithelial trabeculae in septum transversum mesenchyme
- This stopped left liver lobe development
How many cases of right lobe agenesis have been noted in literature? Since when?
19 since 1956
How did most of the reported cases of right lobe agenesis present?
Biliary tract disease
Portal hypertension
How many of the reported cases of right lobe of liver agenesis were incidental findings?
5
What imaging had the patients with incidental finding of right lobe agenesis undergone?
CT
USS
What were the incidental findings of the Radin et al., (1978) study?
5 patients with no right lobe of liver:
- Hypertrophy of other lobes
- 3 also had absent caudate lobes
- Gallbladders lay posterior to medial segment of left lobe (suprahepatic)
- Dilated bile ducts
What were the demographics of the Aktan et al., (2001) study between 1997-1999?
383 patients: - 190 males - 193 females 54 cadavers Ages 32-64 All with no hepatic or parenchyma abnormalities
What did some of the cadavers show in the Aktan et al., (2001) study?
There can be absence of lobes and fusion of lobes without pathological consequences
What did CTs of the patients in the Aktan et al., (2001) study show?
Absence of left or right lobes (partial or complete) may not result in pathology
What were the hepatic parenchyma variations seen in a case study by Saigusa et al., (2001)?
Left lobe: - Not entirely missing (hypoplastic) - No parenchyma - Membranous Right and left hepatic ducts both present
What were the vascular variations seen in the case study by Saigusa et al., (2001)?
Right, left and middle hepatic arteries present
Left branch of portal vein connected to venous and rough ligaments of liver
What organ was absent in the cadaver in the Saigusa et al., (2001) case study?
Gallbladder
What were the hypothesised aetiologies of the variations seen in the Saigusa et al., (2001) case study?
?Disgenesis of hepatic primordium
?Anomalous umbilical vein
?Embolism in/Insufficient growth of left branch of portal vein
?Disorganised nutrient supply