SPLEEN

-By Ankit Beniwal

ANATOMY

• Spleen is the largest organ of lymphatic system in human body.

• Origin:The spleen develops in the cephalic part of dorsal mesogastrium (from its left layer; during the sixth week of intrauterine life) into a number of nodules that fuse and form a lobulated spleen.

• Location: Lies along the axis of 10th rib.• Size: normally varies from 7 to 12 cm.• Formula to assess the size according to age is:• Weight: 150 to 200grams normally

• Blood supply and venous drainage:Arterial supply: Splenic artery which is tortous and is the

largest branch of celiac trunk. Divides into multiple branches just before it enters the hilum of spleen.

Venous drainage: Splenic vein which originates from splenic hilum joins superior mesentric vein to form portal vein behind the neck of pancreas.

• Ligaments: 1. Gastro-splenic .(spleen enlarges in it’s direction)2. Spleno-renal.3. Spleno-phrenic.4. Spleno-colic.• Nerve supply: Sympathetic fibers of celiac plexus

ANATOMICAL VARIATION1. Accessory spleen or splenunculi: • Not uncommon and found in 10-30% of the population.• Mostly lie along the spleen itself(most common site), tail of

pancreas, along splenic artery, at hilum of spleen or in omental ligament.

• They may enlarge after splencetomy.• X-ray: It may appear as mass indenting stomach.• USG: Appears a solid mass which is isoechoic to the spleen.• CT scan: They have density and enhancing characteristics

similar to the rest of the spleen• Splenic scintigraphy: It is the investigation of choice to locate

normal functioning splenic tissue. (Explained further on)

Splenunculi abutting the tail of pancreas

2. Polysplenia: • They are multiple splenic masses seen along normal

spleen or without a normal appearing spleen.• They may vary from 2 to 16 in number.• Present on patient’s left side but may be present

bilaterally.• Associated with other anomalies too, eg: Congenital

heart disease, gut malrotation, IVC anomalies, portal anomalies etc.

3. Splenosis:• When a normal spleen is auto-transplanted or

moved away from it’s usual location due to any trauma to abdomen.

4. Asplenia: Two types-(i) Anatomical asplenia: Absence of spleen

congenitally or iatrogenic.(ii) Functional asplenia: A spleen is seen but it is

non functional.• Splenic fossa appears empty in anatomical

asplenia.• In case of functional asplenia normal functional

tissue can not be traced on splenic scintigrapghy.

SPLENIC TRAUMA

• Spleen is the most common organ to be injured in blunt trauma to the abdomen.

• Accounts for 40% of all solid organ injuries.• Incidence of penetrating trauma of spleen is

relatively low due to low surface area of spleen, which is approx 7% of abdominal surface.

• X-ray: May show a mass in left hypocondrium with or without presence of single or multiple rib fractures. Not of much use though.

• USG: It has become a first line investigation for any abdominal trauma especially for splenic injury. It shows a peri-splenic hematoma with internal echoes along with one or multiple lacerations.

• Isotope scanning: Rarely used now. Used whenit is difficult to identify spleen on USG/CT.

• CT scan: Contrast enhanced CT scan is investigation of choice. It is have high sensitivity, specificity and accuracy (>95%) in detecting splenic injury.

CT grading of splenic rupture.

• In it splenic lacerations appears as linear low attenuation defects that contrast well with high attenuation vascular spleen.

• Intra splenic hematomas appear as more diffuse hypo-attenuating region with irregular margins with splenic swelling.

Grade IV Splenic rupture

Grade III splenic rupture

• Uniform enhancement occurs approximately 50-60 seconds after contrast administration, so imaging during early arterial phase is useful in detection of active extravasation and for pseudo-aneurysms.

• Thing to remember when suspecting splenic injury is that during early phase of enhancement the cord like geographical enhancement of pulp may look like intra-splenic lacerations. So to rule these out a delayed supplementary confirmatory images should be taken.

• Scanning upto pelvis should be done because sometimes hematoma can only be seen as hemoperitonium in pelvis.

• Angiography: It may be used in hemodynamically stable patients with splenic injury diagnosed on CT to detect whether active extravasation is present or not. So that cases who are hemodymanically stable with active extravasation can be treated with bed rest or embolization of splenic artery distal to dorsal pancreatic artery.

Splenomegaly

• X-ray: May show a lump in splenic region with raised diaphragm.

• USG: Enlarged spleen is seen extending downwards, anteriorly and to the right, displacing stomach forwards and medially with left diaphragm seen pushed upwards.

• CT scan: Shows full extent of spleen.

Massive splenomegaly in Gaucher’s disease

Splenic masses

1. Splenic abscess: They are rarely seen in spleen. May be solitary or multiple.

• X-ray: Gas transradiancy is seen i.e. a fluid level is seen within the splenic mass in erect radiograph. It is rarely seen but is enough to make a doagnosis.

• USG: Appearance shows a transition with time. Early stage shows an ill defined mass with decreased reflectivity, which may develop fluid components, debris and septations. In late stage capsule may develop and gas within abscess will be seen as focal areas of high reflectivity with acoustic shadowing.

• TB also causes splenic abscesses, in miliary TB lesions may or may not be identifiable on USG depending on their size.

• Fungal abscess is seen in immunocompromised patients. Usually appears as central area of increased refelctivity which is surrounded by area of decreased reflectivity . If necrosis occurs centrally, the center shows decreased reflectivity and shows ‘Wheel within wheel’ appearance.

Miliary TB

• CT scan: They appear similar to infarcts and hematomas i.e. centrally low density lesions (20-40 HU ) within splenic parenchyma. . Minimal peripheral contrast enhancement may be present when a capsule has developed

Splenic abscess CT

2. Primary splenic malignancy: Very rare in occurance but angiosarcoma can occur as multiple focal lesions.• USG features are non specific and include

splenomegaly with cystic and solid masses with mixed echogenicity.

• CT may show solitary or multiple nodular masses of heterogeneous low attenuation in an enlarged spleen. There are generally irregular and poorly defined contours. Some of these masses may show peripheral enhancement.

3. Metastases: Of all metastases 7% is seen in spleen. Occurs genereally in presence of wide spread metastases elsewhere. Lymphomatous involvement of spleen is relatively common where there is splenic enlargement without an identifiable focal abnormality.These lesions are usually necrotic and are seen as low density lesions on CT. They show ring enhancement on contrast study.On USG they most commonly appear as a hypoechoic lesion, although can be iso- or hyperechoic.

Metastases on CT

4. Splenic cyst: Two types- (i) True cyst: Those containing cellular lining. Eg Hydatid cyst with multiloculated internal structures, epidermoid cyst.(ii) False cyst: Those without cellular lining. They are formed due to previous splenic infarction, infection or trauma.• USG: Well defined anechoic structure with well defined

rounded margin and posterior acoustic enhancement is seen.• CT: Typically shows a hypo attenuating relatively well defined

intrasplenic lesion. The wall is thin and has a demarcation to splenic parenchyma. There is no rim or internal enhancement. Wall calcification may be present.

Hydatid cyst of Spleen

Splenic infarcts

• Most common cause of infarcts is embolism from cardio-vascular disease followed by thrombosis from hematological diseases, eg sickle cell disease, DIC, etc

• USG: They appear as hyporeflective to areflective in acute phase and appear wedge shaped in peripheral location. Chronic infarcts appear as area of increased reflectivity with atrophy of spleen due to scarring.

Multiple and repeated infarcts leads to shrunken spleen known as Auto-splenectomy, seen in Sickle cell disease.

Splenic infarcts on USG shows no blood supply in infarcted region.

• CT scan and Radionuclide scan: Typically seen as localized wedge shaped defects in splenic parenchyma.

In the chronic phase, infarcts may disappear completely, but more commonly, they may reveal progressive volume loss caused by fibrotic contraction of the infarct.

Massive Splenic infarct on CT

Splenic Calcification

• Calcification in or adjacent to the spleen is common, especially after age of 50. Calcific plaque in splenic artery are frequent chance findings on abdominal X-rays.

• Splenic vein calcification is uncommon but may follow portal pyaemia or splencetomy.

• Splenic TB granulomas may produce single or multiple well defined calcification in the parenchyma on X-ray.

• Splenic cyst may show curvilinear or oval calcification.• A complete infarcted spleen appears as small curved

calcified structure.

SPLENIC CALCIFICATION (TB)

MRI in SPLEEN

• Anatomy and internal structures are well shown on CT and USG, but MRI is useful in minority of cases.

(i) Portal hypertension: spleen is enlarged with no change in it’s signal intensity apart from the occasional findings of siderotic nodules (Gamna-Gandy bodies) which produce focal areas of low intensity signals.

(ii) In Transfusion haemosiderosis, the spleen shows generalized loss of signal in both T1 and T2.

(iii) Cysts: unifirm low T1 signal, high T2 signals and no enhancement with gadolinium.

• (iv) Haemangioma: Clear well defined margins with lobulated shape. Uniform low T1 signal and uniform T2 signal. Dynamic imaging after gadolinium shows dense peripheral discontinuous nodular blush, which begins during arterial phase of liver perfusion and continues centripetally for several minutes, so that images taken after 10 minutes often show diffuse hyperintensity of the lesion. Large haemangioma may show unenhanced central core even on delayed imaging.

• (v) Abscess: Rim enhancement on gadolinium is seen in abscess larger than 1.5cm in size. But it is also a feature of metastases with necrotic centers.

Splenic Scintigraphy• Very rarely used or needed now a days.• Physiology: Reticluoendothelial cells of spleen takes up

intravenously injected colloids (99mTc) of size 30-1000nm. In normal cases about 15% of the injected colloidal acitivity reaches spleen, but in patients with cirrhosis or hypersplenism a much greater propoprtion of injected particles will reach spleen and will be trapped there due to increased blood to the spleen.

• A more specific imaging is done by injecting autologus RBC’s which have been incubated at 50° C and labelled with technetium 99. They are called Heat damaged RBCs.

• It is first choice of technique when localization of site of functioning splenic tissue in the absence of a normal spleen on CT or USG, i.e. in cases of polysplenia/asplenia syndrome.

• Autologous platelets labelled with indium-111 is used to demonstrate rate of clearance of circulating platelets in patients with Idiopathic thrombocytopenic purpura, who may be benefited with splenectomy.

Portal Venography

• Methods: (i) Late phase superior mesentric angiography.

(ii) Trans-splenic approach. (Discussed below)(iii) Paraumbilical vein catheterization.(iv) Transjugular transhepatic approach.• Indications: (i) To demonstrate prior to operation the

anatomy of the portal system in patients with portal hypertension.

(ii) To check the patency of a portosystemic anastomosis.

• Technique for Trans-splenic approach: With patient in supine, spleen is identified on USG. Access point must be as low as

possible in the mid axillary line, usually at the level of 10th or 11th intercostal space. The region is anaesthetized. Patient is asked to hold the breath in mid-inspiration and the needle is then

inserted inwards and upwards into the spleen. Blood will flow back if needle is in right place. The patient is then asked to breath as shallowly as possible to avoid trauma to the spleen.

The small test dose of contrast media (LOCM) can be injected to ensure correct siting of the cannula.

When cannula is in right position the splenic pulp pressure can be measured with manometer (10-15 cm H₂O)

A hand injection of 50ml of contrast medium is made over 5seconds and recorded by rapid serial radiography/digital subtraction angiography. Cannula should be removed as soon as possible after injection to minimize trauma to spleen.

Occasionaly portal vein will fail to opacify , owing to major portosystemic collaterals causing reversed floe in portal vein. The final arbiter of portal vein patency is direct mesentric venography performed at operation. The maximum width of normal portal vein is said to be 2cm.

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