Ultrasound of the Abdomen Part II Retroperitoneum Part A Holdorf Ultrasound of the Abdomen Part II

Outline Anatomy Curs of the diaphragm Peritoneum Retroperitoneum Abdominal Aorta Inferior Vena Cava Azygos/Hemiazygos Veins Ascending Lumbar veins Retroperitoneal fibrosis

Crus of the diaphragm The diaphragmatic crura begin as musculo- tendinous fibers arising form the lumbar vertebra and travel along the anterior lumbar vertebrae to insert into the diaphragm. The right cru is broader and longer than the left crus. The right is anteriolateral to the IVC and posteriomedial to the right adrenal and right lobe of the liver. The left cur is lateral to the aorta.

The crus of the diaphragm is located: Anterior to the aorta Superior to the celiac axis Posterior to the inferior vena cava The crus of the diaphragm can be imaged in transverse and longitudinal planes. The curs is located medial and posterior to tall structures except the aorta.

Technique Scanning the retroperitoneum involves scanning the Kidneys, aorta, IVC, pancreas, and pelvic areas. This is usually a general overview scan and not organ specific, unless pathology is discovered in an organ. A 3.5 MHz sector, vector or curvilinear transducer is used although a lower frequency transducer may be needed on larger patients or to image deeper structures. Linear array transducers can be used to evaluate large masses and superficial areas. Longitudinal and transverse scans are performed with the patient in supine and decubitus positions. Scanning will include using the transducer to press bowel gas out of the way to see underlying structures. To reduce bowel gas, patients should be NPO for at least 6- 8 hours.

Laboratory Values Hematocrit levels and red blood cell (RBC) counts will drop with hemorrhage and hematomas. White blood cell counts (WBC) will increase with leukemia, malignancies, infection and abscesses. WBC counts will decrease with Hodgkin’s and non-Hodgkin’s lymphoma. Epinephrine and nonepinephrine will increase with pheochromcytomoas. Cortisol levels can increase in Cushing’s syndrome and decrease in Addison’s disease.  

Masses Adenopathy The lymphatic system consists of small vessels and functioning nodes whose function is to return excess water, electrolytes and colloids to the bloodstream. Normal lymph nodes are too small to see with ultrasound. Enlargement of lymph nodes (Adenopathy) are visible and require careful scanning along the aorta and IVC. The normal distance between the SMA and aorta may be increased, mesenteric and visceral vessels may be displaced, and the aorta may be lifted off the spine when lymph nodes are enlarged. Adenopathy may be regional or extensive.

Enlargement may be due to infection or malignant disease Enlargement may be due to infection or malignant disease. Malignant Adenopathy is commonly caused by metastases or by lymphoma. The most common primary is adenocarcinoma of the GI tract. Lymphatic drainage of the gonads are to the high pre-aortic nodes; therefore ovarian and testicular malignancies may be the cause of upper abdominal lymph Adenopathy.   Sonographically, enlarged lymph nodes are seen in the abdomen as oblong masses of uniform, low level echoes. Superficial lymph nodes are oval or round masses. Enlarged lymph nodes from an infectious process usually have echogenic centers, resembling small kidneys. Arterial and venous blood flow to and from the lymph nodes can be visualized, especially in superficial lymph nodes. Malignant lymph nodes are usually homogenous in appearance.

Lymph Node locations

Enlarged groin Lymph node

Highly vascular malignant lymph node of the neck

Abnormal axillary lymph node with central echogenic fatty hilum

Primary neoplasms are extremely rare and include liposarcoma, leiomyosarcomas. Benign masses include lipomas and fibromas. Some of these tumors can grow quite large before being detected.

Retroperitoneal fibrosis or Ormond's disease is a disease featuring the proliferation of fibrous tissue in the retroperitoneum, the compartment of the body containing the kidneys, aorta, renal tract, and various other structures.

Retroperitoneal Fibrosis is usually idiopathic in origin but may be the result of infections, enteritis (inflammation of the small intestine), or seen in patients on medications for migraines. It can also be associated with leaking abdominal aortic aneurysms. Sonographically, it appears as hypoechoic tissue anterior, posterior or lateral to the aorta or IVC and may look similar to Adenopathy, although it usually does not displace the aorta form the spine and has smoother margins. Since this process extends laterally to the ureters, it may cause Hydronephrosis.  

RETRO-PERITONEAL FIBROSIS

Retroperitoneal Fibrosis Retroperitoneal fibrosis, also known as Ormond’s disease, or inflammatory aneurysm, is a dense fibrous tissue proliferation confined to the para- vertebral region. The fibrosis rarely extends superior to the level of Lkk-2 and may extend inferiorly to the dome of the bladder. Generally, it is centered at the aortic bifurcation. Sonographically, the appearance is usually a hypoechoic midline mass. It is associated with bilateral ureteral obstruction as it envelopes structures rather than displacing them. A large percentage of cases are idiopathic. Other causes include: malignancies various drugs and chemicals Crohn’s disease Sclerosing cholangitis Radiation therapy Chemotherapy Aortic aneurysms

Retro Fibrosis

Hematomas Bleeding may occur into the retroperitoneum, called a hemoperitoneum, as a result of trauma, surgery, leaking or ruptured aortic aneurysms or malignancy. Free fluid or organized collections may be seen on the ultrasound exam. Patients with a leaking aneurysm may present with back pain, flank pain and decreasing hematocrit. Sonographically, complex fluid collections may be observed in the flanks. Suspected leaking aneurysms are a medical emergency and may be a sign of impending aortic rupture.

PERITONEUM The peritoneum is the serous membrane that forms the lining of the abdominal cavity and covers most of the abdominal organs. It consists of two layers: Parietal peritoneum (outer layer)-lines the abdominal wall Visceral peritoneum (inner layer)-covers the abdominal organs. The space between the two layers is the peritoneal cavity. The peritoneal cavity contains two separate compartments:

Peritoneum

Psoas Muscles

Quadratus Lumborum Muscles

Large lymph nodes- causing displacement of the abdominal organs

Malignant lymph nodes w/Liver metasteses

Malignant lymph nodes

Hematomas Abdominal Aorta rupture

The diaphragm PE or Ascites?

Lesser Sac-space that is situated between the liver, pancreas and stomach. The entrance to the lesser sac is the epiploic foramen (area just above the pancreas).   Greater sac- this is the rest of the peritoneal cavity. When you are imaging ascites with Floating bowel, this is the greater sac area.

Inter-peritoneal structures Stomach Jejunum 1st part of the duodenum Appendix Spleen Cecum Transverse colon Rectum (part of) Liver Uterus Fallopian tubes/Ovaries

The stomach to the rectum

Kidneys and adrenal glands lie within the peri-renal space and are separated from the pararenal spaces by the anterior and posterior renal fascia (Gerota’s Fascia).

The following structures are located in the retroperitoneum: Kidneys Adrenal Glands Ascending and Descending Colon 2nd, 3rd, and 4th parts of the duodenum Pancreas Aorta and IVC Ureters Renal vessels Superior mesenteric vessels Gonadal vessels Lymphatics Prostate

Abdominal Aorta The aorta enters the abdominal cavity in a posterior location. It becomes progressively more anterior as it travels caudally. The IVC, in contrast, maintains a more horizontal course throughout the retroperitoneum.

Celiac Axis The celiac axis is the first major branch as the aorta descends through the diaphragm. It is only 2-3 cm long and is located superior to the pancreas. It branches into three arteries Common hepatic artery Left Gastric Artery Splenic artery (the longest of the three) The celiac axis terminates with the bifurcation of the common hepatic artery and the splenic artery (Sea Gull or dove sign) The left gastric artery is usually not visible, however occasionally can be seen extending cranially from the celiac axis. As the common hepatic artery courses toward the liver, it bifurcates into the proper hepatic artery and the gastro- duodenal artery (GDA).

Celiac Axis/trunk

Superior Mesenteric Artery The superior mesenteric artery branches off the aorta about 1 cm inferior to the celiac axis. It parallels the aorta and is seen posterior/inferior to the body of the pancreas. SMA Doppler waveforms: Fasting state- high resistance Postprandial – low resistance-increased velocity NOTE: The celiac should always be low resistant

SMA

SMA

Renal Arteries The renal arteries arise from the lateral walls of the aorta just below the origin of the SMA. The right renal artery passes posterior to the IVC to enter the renal hilum. The left renal artery is shorter as the aorta lies to the left of the midline.

Renal Arteries

Gonadal Arteries The right and left Gonadal arteries arise from the distal aorta and are rarely imaged.

Cartoon of the Gonadal Arteries

Inferior Mesenteric Artery The IMA arises from the anterior aspect of the distal aorta and is rarely imaged.

IMA

Inferior Vena Cava The IVC lies to the right of the aorta and posterior to the pancreatic head and liver. The IVC dilates with cardiac failure and fluid overload. The most common tumor in the IVC is renal-cell carcinoma. Thrombus of the IVC is most commonly caused by Budd-Chari Syndrome. The IVC is easily displaced. The following are reasons for IVC displacement. Liver mass (Medial and lower) Right renal artery aneurysm (anterior) Lymphadenopathy (has tendency to accumulate posteriorly – displace anteriorly Tortuous aorta (right) Right renal /adrenal mass (anterior and medially) Retroperitoneal Tumor

IVC with Hepatic veins

IVC filters IVC filters are used to prevent the ascent of lower extremity vein thrombus. The most common filter is the Greenfield Filter. Proper location for an IVC filter is inferior to the renal veins.

IVC Filter Placement just below the renal veins

Hepatic Veins There are three hepatic veins: right, middle and left, which drain into the IVC.

Hepatic Veins

Renal veins The right renal vein is short, draining directly into the IVC. The left renal vein is longer, passing between the SMA and aorta as it travels from the left kidney to the IVC. The NUTCRACKER SYNDOME is the engorgement of the left renal vein due to its compression by the SMA and aorta.

Renal Veins

Gonadal Veins The right Gonadal vein drains into the IVC. The left Gonadal vein drains into the left renal vein.

Gonadal veins

Azygos/Hemiazygos Veins The Azygos and Hemiazygos veins provide an alternate pathway for venous return in the case of caval obstruction. They connect the proximal abdominal IVC to the superior vena cava and unless dilated, are normally not visualized. The Azygos vein is located on the right. The Hemiazygos vein is located on the left.

Ascending lumbar veins The ascending lumbar veins are branches of the common iliac veins. They are the abdominal counterparts of the Azygos-hemiazygos system. These veins travel in a path lateral to the spine and posterior to the psoas muscle.

Ascending lumbar veins