Revista do Colégio Brasileiro de Cirurgiões
INTRODUCTION
The splenic lesions that have cystic presentation include a range of disorders. We discuss these non-parasitic ones, which are: the primary or true cysts (epithelial, epidermoid), pseudocysts (serous or hemorrhagic), vascular cysts (post-infarction, peliosis) and cystic neoplasms (hemangioma, lymphangioma, lymphoma and metastases).
Splenic cysts are more frequent in the second and third decades of life, but they may appear in other age groups1,2.
In 1829, Andral was responsible for the first description of a non-parasitic cyst of the spleen3. Robbins (1978) reviewed a series of 42,327 autopsies over 25 years, founding 32 patients with splenic cysts. Subsequently, isolated cases have been reported and, in 1978, approximately 600 cases were confirmed in the literature4,5.
Splenic anatomy and physiology
The splenic size and configuration vary. Typical parameters include dimensions of 12 x 7 x 4 cm and a weight of 150 grams (range 100-200 grams) and an anatomic relationship with the bottom of the stomach, the upper pole of left kidney and tail of the pancreas6.
Splenic trabeculae originate in the internal capsule and divide the body into compartments made of a mesh of lymph follicles and reticuloendothelial cells (white cells) interspersed with blood vessels6.
The spleen plays an important role in hematopoiesis, immune function, and protection against infections and malignant diseases6,7. The main hematologic function of the spleen is to act as a filter to remove use erythrocytes, leukocytes, and older platelets from the bloodstream. Its hematopoietic function occurs almost exclusively in fetal life8.
The immunologic function of the spleen is complex. In summary, encapsulated bacteria and parasites are removed from the bloodstream, a cellular response to infection is generated and production of antibodies to face the disease ensues8.
Clinical Presentation
Most cysts are asymptomatic and are diagnosed incidentally during abdominal imaging. The number of splenic cyst diagnosed is increasing, probably due to the large number of radiological examinations currently performed9.
Large cysts of the spleen (greater than 8 cm) may cause pain and weight sensation in the left hypochondrium, whether by splenic capsule distension or compression of adjacent structures10,11. The symptoms of compression on surrounding organs, such as nausea, vomiting, flatulence and diarrhea gradually emerge. In some cases, the effect on the cardiorespiratory system may cause pleuritic pain, dyspnea and persistent cough4,10,12.
Many diseases that affect the spleen have similar appearance on imaging studies. Thus, history becomes very important to help reduce the number of unnecessary tests and diagnostic hypotheses. If a diagnostic uncertainty persists, percutaneous biopsy is useful for elucidation.
Classification
Splenic cysts were classified by Martin13: Type I (primary or real) - are cysts with epithelial capsule, which can be either parasitic or not. Non-parasitic type I cysts may be congenital, vascular or neoplastic; and Type II (secondary or pseudocysts)14, which have no capsule. From the radiological point of view, it is usually impossible to distinguish between primary and secondary cysts.
Congenital cysts (epithelial)
Congenital splenic cysts or epithelial cysts comprise approximately 25% of true splenic cysts11,13, are diagnosed primarily in children and young adults and are usually solitary.
Although the exact mechanism of their etiology, pathogenesis and development is still unknown, proposed mechanisms include: involution of pluripotent cells from the splenic parenchyma during development with subsequent squamous metaplasia; origin from endothelial cells or peritoneal coelomic mesothelium.
At microscopic analysis there is normally a large, smooth, encapsulated cyst and occasionally trabeculae or septa15,16. Microscopically, the cyst is internally lined with columnar, cuboidal or squamous epithelium. They can be subdivided into dermoid, mesothelial, and epidermoid14,17.
Usually congenital splenic cysts are asymptomatic and have a good prognosis. In some cases they may become symptomatic due to increase in size secondary to trauma, cyst wall hemorrhage with an increase in osmolality of cyst fluid, or the presence of stomata in the cyst wall.
Dermoid cysts
These cysts are extremely rare, with few cases reported in the literature. They may contain skin appendages and squamous epithelium in the interior14 and their existence is challenged18 because many of these cysts contain well differentiated tissues. In ectopic location, they can be considered benign teratomas19,20. In Addition, they share the same histological appearance of ovarian dermoid cysts that originate from primordial germ cells19,20.
Pseudocysts
They are called pseudocysts because they do not have capsule21. They correspond to about 75% of parasitic cysts of the spleen. They are secondary to trauma, infection or infarction, trauma being the most common etiological factor. Most are solitary and asymptomatic.
They are believed to be the final stage of organization of an intra-splenic hematoma16,21,22. A remote history of trauma to the upper left quadrant can be often verified.
Macroscopically, they are mostly smaller than true cysts and may contain internal debris. Microscopically, these cysts are composed of dense fibrous tissue, often calcified, with no epithelial lining. They contain a mixture of blood and debris in their interior14.
The appearance on imaging studies is similar to that of true cysts, with density varying with the amount of protein and fibrin existing in the interior22. Some may rupture spontaneously, 70% of ruptures occurring during the two weeks after trauma and 90% within the first month. The interval between trauma and rupture is called "latent period"23. Some pseudocysts increase in size spontaneously or after novel local traumas.
Vascular Cysts
Peliosis
Peliosis is a rare disease characterized by multiple blood-filled cysts located inside the parenchyma of solid organs, mainly in the liver. Exclusively splenic peliosis is a very rare phenomenon. The disease is more common in men24 26.
Although patients are usually asymptomatic, peliosis may become a potentially lethal condition, given that spontaneous rupture of the organ may occur27. If the diagnosis is confirmed, further investigations should be considered to detect the presence of disease in other organs28.
It was initially thought that peliosis occurred exclusively in the organs belonging to the mononuclear phagocytic system, i.e., liver, spleen, bone marrow and lymph nodes28. However, other organs like lungs, kidneys and parathyroid glands may also foster it24. Many etiologic agents have been associated with the occurrence of peliosis28 30, such as toxins (including chronic alcoholism), corticosteroids, oral contraceptives, tamoxifen, azathioprine and androgens.
HIV-positive patients may have opportunistic infectious diseases as an etiological factor31,32. Infectious agents such as hepatitis B or C viruses, Staphylococcus aureus and tuberculosis may be highlighted28-33. Multiple myeloma, Waldenstrom's macroglobulinemia and other malignancies such as Hodgkin's disease, hepatoma and seminoma were also related to the etiology of this disease30,33.
The identification of peliosis can usually be done macroscopically at operation or during radiological investigation. The surface of the spleen may be nodular26; numerous cysts with their cavities filled with blood are found at sectioning of the specimen25. Arteries occasionally protrude into the lumen of the cysts. This may contribute to the lethality of the disease. On CT it is seen as a hypodense cyst, causing no mass effect.
Physicians should be alert to the spontaneous rupture of the spleen, especially in the case of anticoagulation or thrombolysis. In literature there is no indication of surgical exploration of patients in whom the diagnosis was incidental splenic peliosis. Patients should be encouraged to refrain from practicing high-risk activities, such as contact sports. It seems prudent to avoid oral contraceptives. In case of visceral rupture emergency splenectomy should be performed27.
Cystic neoplasms: Hemangioma, Lymphangioma, Lymphoma and Metastases
Lymphoma
Primary splenic lymphoma represents 1-2% of linfomas1,2,4. About 60 cases have been reported till 19834.
Angioma
The most common type of splenic cystic neoplasm is the blood vessel (hemangioma) or lymph vessel (lymphangioma) angioma. Splenic hemangiomas may be capillaries or cavernous34, where the capillaries are mostly composed of blood vessels that are in accordance with the normal caliber of the capillary and cavernous hemangiomas are composed of larger caliber blood vessels35. Lymphangiomas of the spleen are often cavernous36,37. The angiomas are considered congenital, as they are usually present at birth35,36.
The cystic tumors (eg, cystadenomas) are derived from epithelial cells, usually glandular38.
In the case of hemangiomas, the cystic cavity may contain blood. The wall covering consists of endothelium, i.e., the normal lining of the vessels of origin, which was demonstrated by positive immunohistochemical staining with antibodies against factor 8 (endothelial antigen) and by negative staining with antibodies against keratin (epithelial and mesothelial antigen)38.
Metastases
Splenic metastases of solid tumors occur in the terminal phase of the illness, so they seldom have an indication for resection. Tumors arising from the ovaries, lung, breast, stomach, skin and colon may affect the spleen39. The number of cases of isolated splenic metastasis is less than 25 in the world literature.
The lesions may be solid or cystic; on ultrasound, they show varying degrees of echogenicity, but are generally hypoechogenic40. On Computed Tomography (CT) they typically appear hypodense. On Magnetic Resonance Imaging (MRI) they are predominantly hypointense on T1-weighted, and hyperintense in T2-weighted, images. MRI is more accurate for the diagnosis of splenic metastases with necrotic or hemorrhagic contents, which will display heterogeneous images40.
Differential Diagnosis
When a nodule is detected in the upper left quadrant of the abdomen, it is necessary to exclude diseases associated with splenomegaly as mononucleosis, hemolytic anemia, chronic leukemia, collagen diseases and liver diseases that cause portal hypertension41.
Imaging tests
It is difficult to distinguish between true and false cysts both radiologically and histologically.
A plain abdominal radiograph may reveal a mass, which may be calcified, in the left upper quadrant.
Ultrasound can differentiate solid and cystic lesions in most cases. Typically, in ultrasound, the splenic cyst appears as a homogeneous, anechoic mass with thin walls. Septations, irregular walls, or a heterogeneous pattern of internal echogenicity, with debris or hemorrhage and peripheral hyperechoic foci with posterior acoustic shadowing due to calcifications in the wall, can be seen in a complex cyst. Calcifications are useful for differentiating cysts from other causes of splenomegaly4,9,11. An epidermoid cyst has a complex pattern with irregularity and thickening of the posterior wall caused by epithelial trabeculae with peripheral and internal echoes in the interior due to the presence of blood clots11,42.
The spleen is usually heterogeneous on TC, especially during the contrast phase. It is postulated that the reason for this heterogeneity is due to the histological features of the vascular system of the organ, with different rates of blood flow in the red pulp43. One must exercise caution to avoid misinterpretation of this heterogeneity.
Cystic lesions on CT are spherical, well-defined, with attenuation equivalent to that of water, with a thin or imperceptible capsule42 (Figure 1). In one series, cyst wall trabeculation or peripheral septations were found in 86% of true cysts and in 17% of false cysts43. There was also wall calcification in 14% of true cysts and in 50% of false ones42.
The splenic lesions that have cystic presentation include a range of disorders. We discuss these non-parasitic ones, which are: the primary or true cysts (epithelial, epidermoid), pseudocysts (serous or hemorrhagic), vascular cysts (post-infarction, peliosis) and cystic neoplasms (hemangioma, lymphangioma, lymphoma and metastases).
Splenic cysts are more frequent in the second and third decades of life, but they may appear in other age groups1,2.
In 1829, Andral was responsible for the first description of a non-parasitic cyst of the spleen3. Robbins (1978) reviewed a series of 42,327 autopsies over 25 years, founding 32 patients with splenic cysts. Subsequently, isolated cases have been reported and, in 1978, approximately 600 cases were confirmed in the literature4,5.
Splenic anatomy and physiology
The splenic size and configuration vary. Typical parameters include dimensions of 12 x 7 x 4 cm and a weight of 150 grams (range 100-200 grams) and an anatomic relationship with the bottom of the stomach, the upper pole of left kidney and tail of the pancreas6.
Splenic trabeculae originate in the internal capsule and divide the body into compartments made of a mesh of lymph follicles and reticuloendothelial cells (white cells) interspersed with blood vessels6.
The spleen plays an important role in hematopoiesis, immune function, and protection against infections and malignant diseases6,7. The main hematologic function of the spleen is to act as a filter to remove use erythrocytes, leukocytes, and older platelets from the bloodstream. Its hematopoietic function occurs almost exclusively in fetal life8.
The immunologic function of the spleen is complex. In summary, encapsulated bacteria and parasites are removed from the bloodstream, a cellular response to infection is generated and production of antibodies to face the disease ensues8.
Clinical Presentation
Most cysts are asymptomatic and are diagnosed incidentally during abdominal imaging. The number of splenic cyst diagnosed is increasing, probably due to the large number of radiological examinations currently performed9.
Large cysts of the spleen (greater than 8 cm) may cause pain and weight sensation in the left hypochondrium, whether by splenic capsule distension or compression of adjacent structures10,11. The symptoms of compression on surrounding organs, such as nausea, vomiting, flatulence and diarrhea gradually emerge. In some cases, the effect on the cardiorespiratory system may cause pleuritic pain, dyspnea and persistent cough4,10,12.
Many diseases that affect the spleen have similar appearance on imaging studies. Thus, history becomes very important to help reduce the number of unnecessary tests and diagnostic hypotheses. If a diagnostic uncertainty persists, percutaneous biopsy is useful for elucidation.
Classification
Splenic cysts were classified by Martin13: Type I (primary or real) - are cysts with epithelial capsule, which can be either parasitic or not. Non-parasitic type I cysts may be congenital, vascular or neoplastic; and Type II (secondary or pseudocysts)14, which have no capsule. From the radiological point of view, it is usually impossible to distinguish between primary and secondary cysts.
Congenital cysts (epithelial)
Congenital splenic cysts or epithelial cysts comprise approximately 25% of true splenic cysts11,13, are diagnosed primarily in children and young adults and are usually solitary.
Although the exact mechanism of their etiology, pathogenesis and development is still unknown, proposed mechanisms include: involution of pluripotent cells from the splenic parenchyma during development with subsequent squamous metaplasia; origin from endothelial cells or peritoneal coelomic mesothelium.
At microscopic analysis there is normally a large, smooth, encapsulated cyst and occasionally trabeculae or septa15,16. Microscopically, the cyst is internally lined with columnar, cuboidal or squamous epithelium. They can be subdivided into dermoid, mesothelial, and epidermoid14,17.
Usually congenital splenic cysts are asymptomatic and have a good prognosis. In some cases they may become symptomatic due to increase in size secondary to trauma, cyst wall hemorrhage with an increase in osmolality of cyst fluid, or the presence of stomata in the cyst wall.
Dermoid cysts
These cysts are extremely rare, with few cases reported in the literature. They may contain skin appendages and squamous epithelium in the interior14 and their existence is challenged18 because many of these cysts contain well differentiated tissues. In ectopic location, they can be considered benign teratomas19,20. In Addition, they share the same histological appearance of ovarian dermoid cysts that originate from primordial germ cells19,20.
Pseudocysts
They are called pseudocysts because they do not have capsule21. They correspond to about 75% of parasitic cysts of the spleen. They are secondary to trauma, infection or infarction, trauma being the most common etiological factor. Most are solitary and asymptomatic.
They are believed to be the final stage of organization of an intra-splenic hematoma16,21,22. A remote history of trauma to the upper left quadrant can be often verified.
Macroscopically, they are mostly smaller than true cysts and may contain internal debris. Microscopically, these cysts are composed of dense fibrous tissue, often calcified, with no epithelial lining. They contain a mixture of blood and debris in their interior14.
The appearance on imaging studies is similar to that of true cysts, with density varying with the amount of protein and fibrin existing in the interior22. Some may rupture spontaneously, 70% of ruptures occurring during the two weeks after trauma and 90% within the first month. The interval between trauma and rupture is called "latent period"23. Some pseudocysts increase in size spontaneously or after novel local traumas.
Vascular Cysts
Peliosis
Peliosis is a rare disease characterized by multiple blood-filled cysts located inside the parenchyma of solid organs, mainly in the liver. Exclusively splenic peliosis is a very rare phenomenon. The disease is more common in men24 26.
Although patients are usually asymptomatic, peliosis may become a potentially lethal condition, given that spontaneous rupture of the organ may occur27. If the diagnosis is confirmed, further investigations should be considered to detect the presence of disease in other organs28.
It was initially thought that peliosis occurred exclusively in the organs belonging to the mononuclear phagocytic system, i.e., liver, spleen, bone marrow and lymph nodes28. However, other organs like lungs, kidneys and parathyroid glands may also foster it24. Many etiologic agents have been associated with the occurrence of peliosis28 30, such as toxins (including chronic alcoholism), corticosteroids, oral contraceptives, tamoxifen, azathioprine and androgens.
HIV-positive patients may have opportunistic infectious diseases as an etiological factor31,32. Infectious agents such as hepatitis B or C viruses, Staphylococcus aureus and tuberculosis may be highlighted28-33. Multiple myeloma, Waldenstrom's macroglobulinemia and other malignancies such as Hodgkin's disease, hepatoma and seminoma were also related to the etiology of this disease30,33.
The identification of peliosis can usually be done macroscopically at operation or during radiological investigation. The surface of the spleen may be nodular26; numerous cysts with their cavities filled with blood are found at sectioning of the specimen25. Arteries occasionally protrude into the lumen of the cysts. This may contribute to the lethality of the disease. On CT it is seen as a hypodense cyst, causing no mass effect.
Physicians should be alert to the spontaneous rupture of the spleen, especially in the case of anticoagulation or thrombolysis. In literature there is no indication of surgical exploration of patients in whom the diagnosis was incidental splenic peliosis. Patients should be encouraged to refrain from practicing high-risk activities, such as contact sports. It seems prudent to avoid oral contraceptives. In case of visceral rupture emergency splenectomy should be performed27.
Cystic neoplasms: Hemangioma, Lymphangioma, Lymphoma and Metastases
Lymphoma
Primary splenic lymphoma represents 1-2% of linfomas1,2,4. About 60 cases have been reported till 19834.
Angioma
The most common type of splenic cystic neoplasm is the blood vessel (hemangioma) or lymph vessel (lymphangioma) angioma. Splenic hemangiomas may be capillaries or cavernous34, where the capillaries are mostly composed of blood vessels that are in accordance with the normal caliber of the capillary and cavernous hemangiomas are composed of larger caliber blood vessels35. Lymphangiomas of the spleen are often cavernous36,37. The angiomas are considered congenital, as they are usually present at birth35,36.
The cystic tumors (eg, cystadenomas) are derived from epithelial cells, usually glandular38.
In the case of hemangiomas, the cystic cavity may contain blood. The wall covering consists of endothelium, i.e., the normal lining of the vessels of origin, which was demonstrated by positive immunohistochemical staining with antibodies against factor 8 (endothelial antigen) and by negative staining with antibodies against keratin (epithelial and mesothelial antigen)38.
Metastases
Splenic metastases of solid tumors occur in the terminal phase of the illness, so they seldom have an indication for resection. Tumors arising from the ovaries, lung, breast, stomach, skin and colon may affect the spleen39. The number of cases of isolated splenic metastasis is less than 25 in the world literature.
The lesions may be solid or cystic; on ultrasound, they show varying degrees of echogenicity, but are generally hypoechogenic40. On Computed Tomography (CT) they typically appear hypodense. On Magnetic Resonance Imaging (MRI) they are predominantly hypointense on T1-weighted, and hyperintense in T2-weighted, images. MRI is more accurate for the diagnosis of splenic metastases with necrotic or hemorrhagic contents, which will display heterogeneous images40.
Differential Diagnosis
When a nodule is detected in the upper left quadrant of the abdomen, it is necessary to exclude diseases associated with splenomegaly as mononucleosis, hemolytic anemia, chronic leukemia, collagen diseases and liver diseases that cause portal hypertension41.
Imaging tests
It is difficult to distinguish between true and false cysts both radiologically and histologically.
A plain abdominal radiograph may reveal a mass, which may be calcified, in the left upper quadrant.
Ultrasound can differentiate solid and cystic lesions in most cases. Typically, in ultrasound, the splenic cyst appears as a homogeneous, anechoic mass with thin walls. Septations, irregular walls, or a heterogeneous pattern of internal echogenicity, with debris or hemorrhage and peripheral hyperechoic foci with posterior acoustic shadowing due to calcifications in the wall, can be seen in a complex cyst. Calcifications are useful for differentiating cysts from other causes of splenomegaly4,9,11. An epidermoid cyst has a complex pattern with irregularity and thickening of the posterior wall caused by epithelial trabeculae with peripheral and internal echoes in the interior due to the presence of blood clots11,42.
The spleen is usually heterogeneous on TC, especially during the contrast phase. It is postulated that the reason for this heterogeneity is due to the histological features of the vascular system of the organ, with different rates of blood flow in the red pulp43. One must exercise caution to avoid misinterpretation of this heterogeneity.
Cystic lesions on CT are spherical, well-defined, with attenuation equivalent to that of water, with a thin or imperceptible capsule42 (Figure 1). In one series, cyst wall trabeculation or peripheral septations were found in 86% of true cysts and in 17% of false cysts43. There was also wall calcification in 14% of true cysts and in 50% of false ones42.
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