computed tomographic evaluation of the retroperitoneum in infants and children

JOURNAL OF COMPUTED TOMOGRAPHY 1983;7:63-75

COMPUTED TOMOGRAPHIC EVALUATION OF THE RETROPERITONEUM IN INFANTS AND CHILDNEN

PHILIP STANLEY

With many retroperitoneal diseases in infancy and childhood, computed tomography will give infor- mation unavailable by any other single imaging technique. This maxim applies particularly to the adrenal, where the bercolating nature of neuroblastoma with its propensity toward spinal involvement is exquisitely shown with computed tomography. Renal neoplasms and trauma can be illustrated ef- fectively with computed tomography, as can pancreatic disease and spinal and paraspinal inflammatory and neoplastic disease. In addition to diagnostic studies, computed tomography may be used as guidance for invasive procedures.

KEY WORDS:

Computed tomography; Adrenal; Kidney; Spine; Tumor; Inflammation; Trauma

INTRODUCTION

It is for suspected disease in the retroperitoneum that abdominal computed tomography is most frequently performed at Childrens Hospital of Los An- geles. The retroperitoneum can be conveniently defined as the space lying between the posterior parietal peritoneum and the fascia transversalis. This area can be further divided into three spaces whose anatomical boundaries are often visible on axial tomography. The anterior pararenal space lies between the posterior parietal peritoneum and the anterior renal fascia (Zuckerkandl’s fascia]. It con-

The Department of Radiology, Childrens Hospital of Los An- geles, Los Angeles, California

Address reprint requests to: Philip Stanley, M.D., Department of Radiology, Childrens Hospital of Los Angeles, P. 0. Box 54700, Los Angeles, California 90054.

Received August 5, 1982; accepted August 5, 1982. C 1983 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017 0149-936x/83/010063-13$3.00

tains the pancreas and retroperitoneal portions of the descending duodenum and asuending and descending colon. The perirenal space is between the anterior and posterior renal fascia, containing as it does the kidneys and adrenals. If the space on either side is extended to the midline, the major vascular structures are included. The posterior pararenal space is between the posterior renal fascia (Gerota’s fascia] and the fascia transversalis. It con- tains no important organs.

On account of the anatomic orientation of the retroperitoneal organs and separating fascial planes and vascular structures, this region is particularly suitable for display by axial computed tomography (CT) -

Neoplastic disease of the kidney or adrenal is the most common indication for CT, fiollowed by suspected malignant lymphadenopatby. Trauma and inflammatory disease account for a lesser number of examinations.

The following sections describe the technique for demonstrating retroperitoneal disease, along with various examples of pathology contained therein.

SEDATION

Patient movement causes severe degradation of the computed tomographic image even with an ultrafast machine. In children under 6 years of age, sedation is given unless there is a proven higtory of quietness and cooperation during the examination. Nothing is given orally for 4 hours before the examination ex- cept for essential medicines which may be taken with a small amount of water. For children under 2 years of age, chloral hydrate is given orally 30-45 minutes before the examination; this can be followed by orally administered contrast medium. (The dose is 50 mg/kg of chloral hydrate with a maximum of 2 g. For a particularly anxious child, this may be increased to 75 mg/kg.) We have had no

64 STANLEY THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 7. NO. 1

problems with aspiration of regurgitated gastric contents with this dosage. In older children, between 2 and 6 years of age, demerol-phenergan- thorazine mixture (DPT) is given by intramuscular injection. The dose of the mixture (demerol 25 mg/ ml, phenergan 6.25 mg/ml, and thorazine 6.25 mg/ ml) is 1 ml/lOkg with a maximum of 2 ml. This should not be repeated. If the child becomes very drowsy and swallowing is impaired, then oral contrast medium is not given. When a child is under heavy sedation, an electrocardiographic monitor is used, and the child is continuously observed either directly through a lead glass observation panel or through closed circuit television. For a very active child on whom it is essential to obtain a scan, intravenous Valium (0.2 mg/kg maximum dosage) is carefully and patiently titrated intravenously. The dosage of sedation and its effectiveness is recorded for each patient in a book so that it may be modified if necessary on subsequent visits. It should be re- membered that this is a diagnostic examination that should have low morbidity and no mortality. Do not add to the morbidity by overenthusiastic or hurried sedation. Everyone who works in the CT room should have experience in basic resuscitative procedures.

hour before the examination. If a pelvic mass is sus- petted and the oral contrast medium has not reached the rectum, then dilute contrast solution, of the same strength as the oral agent, can be given rectally in the form of a small enema.

INTRAVENOUS CONTRAST MEDIUM

Unless the patient is allergic to the agent, intravenous contrast medium is always given; for some examinations, particularly if liver metastases are not suspected, only a postenhancement scan is required. This is especially so with follow-up examinations, e.g., neuroblastomas, lymphadenopathies, and abscesses. Intravenous contrast medium will opacify the kidneys, ureters, and bladder. If given as a bolus, the major vascular structures (e.g., aorta and main branches and inferior vena cava) will be opacified and enhancement of hypervascular tumors will be apparent. In addition, contrast medium will increase accentuation between the tumor and host tissue (e.g., Wilms’ tumor). It should be noted that hepatic metastases may be hypodense on preenhancement studies but isodense after the use of contrast medium. It is for this reason that both pre- and postenhancement studies are performed in patients with suspected liver metastatic disease. Two milliliters of 60% contrast per kilogram of body weight given intravenously with a maximum of 100 ml. If the child is an inpatient, an intravenous line with a 1% or 21-gauge butterfly needle is placed on the ward before coming to the CT area so that the agitation of venepuncture does not disturb the child during scanning. For outpatients, the pro- cedure nurse sets up the intravenous line before the scout film is taken. If vascular structures and tumor vascularity are to be evaluated, then half the contrast medium is given as a bolus, the scanning is started, and the remainder is infused slowly. It is inadvisable to give contrast medium into a lower limb vein, as the high level of medium in the inferior vena cava causes excessive scatter, which de- grades the image.

ORAL CONTRAST AGENTS

If at all possible, oral contrast medium is always given before abdominal scanning. Nonopacified loops of bowel may be confused with masses, lymphadenopathy, and normal structures. The se- cret to satisfactory bowel opacification is to give plenty of dilute contrast medium well ahead of the examination. The contrast medium is a 3% solution of Gastrografin or Hypaque diluted and made more palatable with orange juice or punch. It is an error to make the solution too strong. High-density scatter streaking will obscure the adjacent structures. For this reason also it is important that the bowel is clear of barium residue before the scan is performed. (Surgical clips can be equally as destructive to the scan.) If there is excessive scatter from a contrast fluid level-air interface in the stomach, then this artifact can be reduced by scanning in a right lateral decubitus position (see below).

For children under 1 year of age, 50-60 ml of contrast medium is given, increasing to 250 ml by 6 years, and up to 600 ml by 12 years of age and over. For pathology within the upper abdomen, the contrast medium is given 1 hour before the scan; for the lower abdomen, 2-3 hours beforehand, and for suspected pelvic disease, the contrast medium is given 3-4 hours before the study with a repeat dose an

INTRATHECAL CONTRAST

In those patients in whom the plain films or other imaging studies suggest paravertebral pathology, or when the disease has a known propensity towards vertebral or intraspinal spread, the examination is performed with intrathecal metrizamide. This is often combined with examination of the cerebrospi- nal fluid for malignant cells, which is part of the protocol before starting chemotherapy with many tumors, especially neuroblastomas. As a premedi-

FEBRUARY 1983 RETROPERITONEUM 65

cation not only to sedate the patient, but also to pre- vent seizures that have occasionally been reported with metrizamide, phenobarbitone is given before the study (5 mg/kg to a maximum of 130 mg). In older children, the phenobarbitone is given intravenously. For infants, it may be given as an elixir. A limited myelogram is performed through the level of suspected involvement by using metrizamide at a concentration of 220 mg I/ml. In the newborn, l- 1.5 ml of metrizamide is given, increasing to 12 ml for children 10 years old or older. The patient is scanned 2-3 hours later when the contrast medium is more dilute. An alternative is to use a smaller volume of more dilute metrizamide (180 mg I/ml) with immediate scanning without a preceding routine myelogram.

SCANNING TECHNIQUE The transverse or axial plane is used routinely and, if necessary, sagittal and coronal reconstruction can be performed later from the computed data. With a small child, it is possible to perform direct sagittal scans with a wide gantry; if the child can sit up in the gantry; direct coronal scans may be performed. Images in the sagittal and coronal planes, although not routinely obtained for diagnosis, are most useful to the radiation therapist in portal planning and iso- dose determination.

The patient is restricted if necessary by a wrap- around blanket of a ‘Velcro’ tape harness and placed in the scanner. Most patients are scanned in a supine position, but if there is suspected lymphadenopathy, the prone position may be used to com- press the bowel against the spine, thus accentuating the retroperitoneal nodes. A right lateral decubitus position is occasionally used to minimize the contrast flare from the stomach. The operator selects the field of view and radiographic factors. If coop- erative, most children can suspend respiration for the duration of the scan, which varies between 2 and 9.6 seconds, depending on the scanner. With sedation, quiet respiration during the scan causes very little image degradation.

The normal technique at this institution is to perform l-cm thickness slices at l-cm intervals in children below 10 years of age and 1.5-cm intervals above this age, depending upon the nature of the underlying pathology. With suspected adrenal hyperplasia, 5-mm sections are taken at 5-mm intervals. Not only is the retroperitoneal area examined, but with tumors, the liver and chest are included.

Window dimensions and display format are important when examining the retroperitoneum. The usual viewing window width is 300-500 units, the

lower value being used when there are limited contrast differences. At this level, however, the image tends to be grainy. With more inherent contrast, high values are used; for spinal viewing, widths of 1000 units are preferred, particularly if metrizamide has been introduced. Often it is visually more ac- ceptable to reverse the black and white display with spinal viewing. The window level is adjusted on the monitor to give the right degree of penetration.

PATHOLOGY Kidney Computed tomography is used extensively in the diagnosis of pediatric renal disease. The most frequent indication is demonstration of renal tumors, followed by trauma, inflammatory disease, and occasionally, with renal calcification, renal obstruction, and cystic disease. The complications associ- ated with renal transplantation may also be visualized by this modality. The resolution of the scanner is insufficient at the present time ‘to allow demonstration of discrete vascular lesions by computed tomography.

Tumors

wnMs’.-The most frequent renal tumor seen in the pediatric population is Wilms’ tumor. Com- puted tomography confirms the presence of the tumor and shows its extent within the kidney, as well as any involvement of adjacent structures. Spread into the renal vein and inferior vena cava is demonstrated along with nodal and hgpatic metastases. A second mass within the opposite kidney will be apparent, and inclusion of the chest is the best method to demonstrate pulmonary metastases. An- atomic variants, e.g., horseshoe kidney-which may not be visualized by other imaging techniques but have an important bearing on therapy-will also be shown by computed tomography:. Not only is CT the best way initially to demonstrate the size and extent of a Wilms’ tumor, but it is most useful for follow-up studies, demonstrating shrinkage by chemotherapy of an initially unresectable mass, and for following up the renal fossa to detect recurrence after surgery.

The introduction of CT has altered the approach to the diagnosis of renal masses. If a solid renal mass is discovered on ultrasonography, a computed tomogram is performed, both before and after intravenous contrast medium enhancement. At the end of the examination, a single film of the abdomen is taken, the equivalent of an intravenous urogram,

66 STANLEY 1 ‘HE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 7, NO. 1

FIGURE 1. There is a large intrarenal tumor of diminished density on the right side compared with the enhancing kidney remnant, which is displaced medially. Histology revealed a Wilms’ tumor.

which has now been almost completely replaced by computed tomography in the initial diagnosis of renal tumors.

On a CT scan, a Wilms’ tumor is of lower density compared with normal kidney, and the difference is accentuated by intravenous contrast medium enhancement (Figure 1). Large tumors, especially if treated with chemotherapy or radiation, often contain areas of further diminished density within the tumor indicative of tumor necrosis [l] (Figure 2). Calcification within the tumor may occur, but it is rare [2], The tumor is usually well defined, having a pseudocapsule. As to be expected, there is defor-

FIGURE 2. There are rounded areas of diminished density within a large lower polar left Wilms’ tumor. These areas were found to represent necrosis at surgery.

mity and obstruction of the underlying collecting system. Blood clots may be visualized within the renal pelvis. There may be no visualization of the collecting system of the kidney because the venous drainage is blocked by a tumor. In this situation, there is enlargement of the renal vein and inferior vena cava with a large filling defect of the same density as the primary renal tumor (Figure 3). Oc- casionally, this filling defect will be surrounded by contrast medium if the cava is incompletely blocked. With complete obstruction paravertebral and abdominal wall collaterals may be visible. A

FIGURE 3. [A) There is enlargement of the inferior vena cava (I) with tumor completely replacing the lumen. A Wilms’ tumor is occupying much of the right kidney, with a large anterior extension (T). (B) After chemotherapy, the inferior vena cava is of normal caliber and does not contain tumor. There is a small residual tumor “scar” on the anterior margin of the right kidney. The lower pole of the spleen is partially obscuring the left kidney. Fur- ther sections showed no abnormality in this kidney.


bolus of intravenous contrast medium will often vi- sualize the renal, celiac, and superior mesenteric arteries and the aorta. These may all be displaced by an extensive tumor.

Nodal involvement is difficult to assess in children. If extensive, it should be visible on a CT scan, but subtle enlargement can be missed. A very large tumor will displace the stomach and bowel away if arising from the left kidney; on the right side, a large tumor will extend into the right lobe of the liver. Several patients have been referred to this institution with an incorrect diagnosis of a primary hepatic tumor in the right lobe whereas lower sections have demonstrated that the tumor arose from the kidney (Figure 4). Also, a Wilms’ tumor may ex-

FIGURE 4. (A) This section through the upper liver discloses a large mass with a necrotic center initially diagnosed as a primary liver tumor at an outside institution. (B) Lower sections with intravenous contrast show defor- mity of the right collecting system with an intrarenal mass extending anteriorly with a large extrarenal component. This was a large Wilms’ tumor extending high into the right lobe of the liver.

tend into the chest via the retroperitoneal space. The origin of these extensive tumors may be difficult to establish at times, although there is often localized calyceal obstruction or displacement typical of an intrarenal mass (Figure 5). A tumor this extensive cannot be completely removed: by surgery, and it may be difficult with other large but not so extensive tumors to assess operability. A’ large tumor extending into the liver may have a thin, but surgically important plane of separation; a large left- sided tumor, even crossing over the midline, may also be successfully removed. Involvement of the inferior vena cava and right atrium’calls for special surgical techniques for complete removal of the tumor. Very rarely, the primary tumor may extend into the spinal canal destroying bone, obliterating the epidural fat, and displacing the spinal cord. In our institution, this is more common with metastatic Wilms’ tumor in the thoracic spine.

A tumor in the opposite kidney usually has the same density characteristics as thesother kidney tumor, but not always (Figure 6). Artieriography is often employed in this situation if l~ocal surgical ex- cision of the tumors is to be undertaken.

As part of the initial evaluation, the chest and liver are scanned although in our experience pulmonary metastases are uncommon, and liver metastases very rare at the time of presentation.

LYMPHOMA. Some experience has been gained with CT in pediatric renal lymphoma [l]. The disease is usually bilateral with diffuse involvement and ill-defined margins (Figure 7). In addition, there may be enlargement of adjacent lymph nodes and hilar lymphadenopathy. It should be noted that, however, based on CT alone it may be difficult to separate a discrete lymphomatous mass from a Wilms’ tumor.

ANGIOMYOLIPOMA. Renal involvement by tuberous sclerosis may be manifested in two ways: the presence of discrete tumors (angiomyolipomas) and cystic disease, both of which may be detected by CT. Angiomyolipomas are seen as masses with lucent centers of fatty density with multiple flecks of calcium [3]; the cysts are often small; lying within the renal cortex or adjacent to it. It should be noted that small angiomyolipomas may be missed on CT. In a patient with apparent unilateral disease and hematuria, in whom surgery is contemplated, the other kidney should be studied arteriographically.

OTHER RENAL TUMORS AND TUMdRLIKE CONDITIONS.

Metastatic disease to the kidney is rare but may

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FIGURE 5. (A) There is a large pleural based mass en- croaching on the right lung displacing the mediastinum to the left. (B) A high nonenhanced abdominal scan shows right sided hydronephrosis with an anterior intrarenal mass (M). (C) A lower section reveals a lower pole mass with some areas of tumor necrosis. Surgery con- firmed the presence of an extensive Wilms’ tumor.

FIGURE 6. There are bilateral Wilms’ tumors seen on this scan performed after contrast medium enhancement. The tumor on the right side is occupying the midsection and that on the left, the posterior half. There are areas of necrosis on the left after chemotherapy.

simulate a primary renal tumor although, in one patient with metastatic osteogenic sarcoma, the metastatic deposit was of greater density than the host kidney (Figure 8). Nephroblastomatosis will show bilaterally enlarged kidneys on CT scans with slightly lobulated outlines and a nonenhancing peripheral rind of tissue.

Trauma. Computed tomography has an important place in the diagnosis of renal trauma. For mi- nor trauma with microscopic hematuria, a limited intravenous urogram is sufficient. However, with major and nonpenetrating trauma-especially if there is suspected liver and spleen damage-CT is the method of choice for initial evaluation once the patient’s condition has been stabilized. In this situation it is unnecessary to perform a preenhancement study. A single plain film of the abdomen after the CT scan with contrast-medium enhancement is helpful not only in complementing the scan findings, but also in demonstrating the ureters in full length with a view of the bladder. (With improved “scout” view, this latter film may not be necessary.)

The most serious consequences of trauma are avulsion of the renal pedicle or complete thrombo- sis of the renal artery. When either of these catastro- phes occur, the kidney will be visible, but it will not enhance. If there is very poor contrast-medium enhancement with filling of spidery calyces but no other evidence of renal damage, then a dissection of the renal artery is suspected and arteriography is undertaken.

The important renal trauma lesion of parenchy-


FIGURE 7. (A) The scan performed after contrast-medium enhancement reveals a large tumor mass of diminished density replacing and expanding the upper pole of the right kidney. In addition, there is a diffuse involvement of the left kidney. This is an example of bilateral renal lymphoma. (B) A scan after contrast-medium enhancement at the level of the renal hilus showing an ill- defined mass of reduced density within the left kidney. The patient has disseminated lymphoma. (Not the same patient as in A.)

ma1 damage, which may involve the collecting system, can easily be shown with CT [4]. A break in the renal substance is readily demonstrated along with a subcapsular collection (Figure 9). Maceration of the kidney will be shown as fragments of kidney split apart with blood and contrast-medium-laden urine interspersed. A urinoma will be obvious as a collection of fluid outside the collecting system the density of which will increase with subsequent scans.

In addition to showing the extent of the trauma to the affected kidney, CT will demonstrate the other kidney as well as the liver and spleen.

Inflammatory disease. Computed tomography is an excellent modality for demonstrating renal car- buncles and perirenal inflammatory disease, but it has little or no part in the diagnosis of chronic pye- lonephritis although characteristic images have been reported. [5] With a renal abslcess, there is an area of diminished density that may be moderately well defined, and there may be some displacement of the collecting system. Peripheral enhancement with an irregular inner margin may be seen after a bolus of intravenous contrast medium. Usually there are characteristic clinical feaitures to support the radiologic diagnosis of a renal abscess. Com- puted tomography may be used ati a guideline for percutaneous drainage of an abscess.

FIGURE 8. (A) On this scan without contrast-medium enhancement, there is a tumor of increased density occupying the posterolateral aspect of the right kidney. (B) This subscapular mass is now highlighted by the adjacent, enhanced kidney. This tumor was metastatic osteogenic sarcoma.

io STANLEY THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 7, NO. I

Adrenal

Computed tomography is the imaging method par excellence for visualizing adrenal disease. Com- puted tomography is used most frequently to diag- nose adrenal tumors, but hyperplasia, abscesses, and hematomas may all be evaluated with this modality.

FIGURE 9. A scan after contrast-medium enhancement in this trauma victim reveals a renal parenchymal break anteriorly (asterisk) with a perirenal collection of fluid (arrows). Conservative therapy was successfully pursued.

Renal Calcification. The presence of calcification and its exact site within or adjacent to the kidney can be easily demonstrated by a few judiciously placed CT sections [5].

Renal Obstruction and Cystic Disease. Com- puted tomography has a very limited role in the primary diagnosis of obstructive hydronephrosis, although obstruction may be seen on scans performed for another purpose, e.g., a large pelvic mass. Ultra- sonography and radionuclide renograms are the most helpful studies with uncomplicated severe renal obstruction.

Although characteristic features of infantile poly- cystic disease have been described with CT [5], intravenous urography and ultrasound are equally as efficacious, and they are easier and cheaper to perform. With multicystic disease, ultrasonography and renal radionuclide scans are simpler and do not require an injection of intravenous contrast medium to make the diagnosis.

Kidney Transplant. Computerized tomography has no part in the routine investigation of live, re- lated, potential renal donors, but may be useful in demonstrating the nature and extent of fluid collec- tions around a transplanted kidney. Usually the first investigation in the latter situation is ultrasonography. Computed tomography is not useful in di- agnosing rejection or renal artery stenosis, the former requiring isotope scans and the latter, angi- ography.

Tumors

NEUROBLASTOMA. The very origin and method of spread of this tumor lends itself to exquisitely diagnostic studies with CT. The examination is modified slightly, depending upon the patient’s age and findings on other imaging modalities. Below 6 months of age, metastatic liver involvement is to be expected along with the primary tumor. If the plain film or other imaging modalities show evidence of paravertebral disease, then metrizamide is introduced into the lumbar space before a scan is performed (see above].

Neuroblastomas have certain characteristic features on CT scans. Calcification-which is usually nodular and may be in multiple sites within the tumor-is visible in about 95% of patients (Figure 10). The tumor tends to invade and permeate through adjacent structures. The ipsilateral kidney is displaced downward and laterally, and the hilus is often invaded. The aorta is frequently elevated from the spine, being surrounded by tumor and separated from the inferior vena cava. (These vascular struc-

FIGURE 10. A scan without contrast-medium enhancement revealing a large neuroblastoma compressing the liver and displacing the stomach anteriorly. There are areas of nodular calcification within the tumor.


FIGURE 11. A scan, performed after a bolus injection of contrast medium shows a large neuroblastoma with a variegated appearance due to areas of increased vascularity intermingled with necrosis within the tumor. The aorta [arrow) is elevated by retrocrural disease. Metrizamide is present in the spinal canal.

tures will be visible on bolus contrast studies [Fig- ure 111). In addition, the celiac axis and superior mesenteric arteries may be encased by tumor. The diaphragmatic crura are often thickened and displaced anteriorly by retrocrural nodes (Figure 12). Neuroblastomas tend to invade the spinal canal through the intervertebral foramen. Computed tomography with intrathecal metrizamide is the only established method of demonstrating bony destruc- tion along with extra- and intraspinal involvement in a single examination [6]. In those patients in

FIGURE 12. Partially calcified neuroblastoma is present beneath the elevated, thickened crura.

whom metrizamide has not been used, it may still be possible to detect intraspinal involvement by showing displacement or obliteration of the fat surrounding the spinal cord [7,8].

On preenhancement films, the noncalcified ele- ments of the tumor are less dense than the adjacent kidney. After bolus injection of intr@venous contrast medium, large tumors often have 1a variegated appearance with areas of increased vascularity interspersed with islands of diminished density (Fig- ure 11).

Local spread to paraaortic nodeis will be shown on CT as well as invasion of the liver either by adjacent tumor or by multiple metastases in the youn- ger patients (Figure 13).

After removal of the primary tumor, or with treatment by radiation and chemotherapy, CT is an excellent modality for subsequent examinations. In addition to scanning the abdomen, the chest is also included if preliminary scout f&s indicate the possibility of intrathoracic paravertebral disease.

PHEOCHROMOCYTOMA. This is a rare tumor in childhood, but it is an important, treatable cause of hypertension. At Childrens Hospit of Los Angeles, CT has changed the radiologic evaluation of children with urinary and peripheral blood evidence of a pheochromocytoma, which has yet to be localized anatomically. If the biochemical studies suggest an adrenal location, then CT is first performed. If an extraadrenal site is suggested (by high norepineph- rine levels], venous sampling is first performed to localize the tumor more closely, hollowed by a CT

FIGURE 13. Multiple hepatic metastaees are present from a calcified neuroblastoma on the left side in this s-month- old girl. In addition, there are two enlarged retrocrural nodes.

72 STANLEY THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 7, NO. I

scan of the area indicated by venous blood analysis. Arteriography is most unlikely to detect a tumor missed by CT, but is useful before surgery in demonstrating important arterial anatomy with large masses.

About 5% of pheochromocytomas will show areas of calcification due to old hemorrhages or necrosis [9]. There is frequently an enhancing circumferential shell about the tumor [lo] (Figure 14). The tumor is most frequently in the adrenal area, but it may arise anywhere along the sympathetic chain. With multiple endocrine syndromes, type II and III, bilateral tumors are found and may be malignant [9]. Venous invasion is unusual with malignant pheochromocytomas, but it can be shown by CT which will also demonstrate hepatic, lymph node, and lung metastases [ll].

ADRENAL CORTICAL HYPERFUNCTION. With hypercortisolism, CT will distinguish between a primary adrenal cause and pituitary-dependent disease. With normal or symmetric hyperplasia of the adrenals, the hypercortisolism is due to overproduction of adrenocorticotrophic hormone by the pituitary, usually a microadenoma [9]. The pituitary should also be examined by CT in preparation for a trans- sphenoidal surgical approach. Rarely, macronodu- lar hyperplasia may be present due to pituitary hyperfunction. A unilateral adrenal mass indicates a primary adrenal cause. A small tumor (less than 5 cm) is compatible with an adenoma; a larger mass suggests a carcinoma. Venous invasion with a carcinoma may be seen on a CT scan.

FIGURE 14. A study, performed after contrast-medium enhancement, which discloses a rounded mass lying inferior to the lower pole of the left kidney. There is circumferential enhancement in this surgically proven pheochromocytoma.

Hyperaldosteronism (Conn’s syndrome) is rare in children. Because an adenoma may be small and below the resolving power of CT, venous sampling and venography may be required to distinguish between a solitary tumor and hyperplasia [9].

ADRENAL HRMATOMA AND ABSCESS. Adrenal hema- toma in the newborn, which may later become sec- ondarily infected, can easily be shown by CT. How- ever, it is usually investigated with intravenous urography and ultrasound, which together with the typical clinical features and normal urinary vanilyl mandelic acid levels enable the correct diagnosis to be made. The natural regression of the hema- toma can be satisfactorily documented with ultrasound.

Pancreas Pancreatic disease, relatively common in adults, is rare in children. Even so, CT will show primary tumors and metastatic disease around the pancreatic head, calcific pancreatitis, fat and iron replacement, and the effects of trauma-particularly pseudocyst formation.

Primary pancreatic tumors that may be hormonally active are unusual in children. If large enough, the tumor will be visible on a CT scan and may contain calcium (Figure 15). If the tumor is hormonally active, the route of investigation follows that established for adults by Doppman et al. [9]. Metastatic disease to the lymph nodes around the pancreatic

FIGURE 15. There is a large mass in the head of the pancreas with an area of central lucency and an adjacent nodule of calcification. This proved to be a non-p-cell adenoma.

FEBRUARY 1983 RETROPERITONEIJM 73

FIGURE 16. A large mass of nodes in the region of the pancreatic head is present in this teenager with multifo- cal hepatocellular carcinoma.

head is easily demonstrated by CT (Figure 16). Dila- tation of the biliary system secondary to obstruction should be obvious on the scan.

Primary colonic masses may invade the pancreatic head. If they are mucous secreting, floccu- lent calcification may be detected by CT (Figure 17).

Fatty replacement or infiltration of the pancreas is seen in cystic fibrosis [12] and in metaphyseal chondrodysplasia with pancreatic insufficiency and neutropenia (Schwachman syndrome). This can be beautifully shown on CT, as can deposits of calcium in calcific pancreatitis and iron in thalassemic chil-

FIGURE 17. A large mass with speckled calcification lies anterior to the right kidney. This is an extensive mucus- secreting carcinoma of the colon with hepatic metastases.

FIGURE 18. This 18-month-old chilcl with a histologi- cally proven rhabdomyosarcoma has + large retroperitoneal mass with pathological calcification and invasion of the hilus of the left kidney. This appearance is identical to that seen in neuroblastoma.

dren receiving multiple blood transfusions [ 131. Pseudocyst formation usually seen after trau-

matic pancreatitis can be demonstlrated by CT, but it is probably best diagnosed and followed up by ultrasound [ 11.

Other Retroperitoneal Tumors

Retroperitoneal rhabdomyosarcomas can have identical features to neuroblastomas exicept that involvement of the spine and contents occurs less fre-

FIGURE 19. There is a large cystic qass adjacent to the enhanced left kidney with a more solid component extending anteriorly. There are enlarg4d preaortic nodes. This rhabdomyosarcoma extended intb the chest.

74 STANLEY THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 7, NO. 1

Blood Vessels

FIGURE 20. A scan after injection of contrast medium shows a partially enhancing mass surrounding the right colon. This was found to be a hemangioma at surgery.

Aneurysms of the abdominal aorta and complications thereof are readily detected by CT in adults, but there have been few descriptions of CT of pediatric aortic disease, admittedly a rare occurrence [l&15]. However, abnormalities of the venous system are more frequent. A tumor or blood clot within the inferior vena cava can be easily demonstrated with CT, particularly if calcified. Anatomic variants, with azygous or hemiazygous continuation of the inferior vena cava and duplication of the inferior vena cava, may be detected and can simulate lymphadenopathy unless contrast-medium-enhancement studies are performed. With portal hypertension, dilatation and tortuosity of the splenic, superior mesenteric, and portal vein, along with retroperitoneal collaterals may be visible.

quently. The tumor will encircle and displace major blood vessels, invade the renal hilus, and displace the kidneys laterally (Figure 18). Calcification may be present along with heterogeneous enhancement after administration of intravenous contrast medium. Occasionally, rhabdomyosarcomas may have a low-density cystic component that can be easily evacuated at surgery (Figure 19).

There are rare benign retroperitoneal tumors which can be demonstrated by CT. Lymphangiomas and hemangiomas may surround the bowel and have large contrast-medium-enhancing spaces within them (Figure 20).

Lymphadenopathy

In adults, CT is an extremely efficient method of de- tecting lymphadenopathy, and measurements have been established giving the upper dimensions of normal lymph nodes. This diagnostic ease is not seen with pediatric patients because of the lack of fat that separates individual nodes in the adult. Also, loops of unopacified bowel may simulate lymphadenopathy [ 71. Even so, lymphadenopathy may be confidently diagnosed in some patients (Fig- ure 19). Prone as well as supine scanning is some- times helpful. Because many treatment protocols require a staging laparotomy for lymphomas, inde- pendent of the results of abdominal imaging, only limited attention has been paid to the initial detec- tion of lymph node disease. However, it is a field that requires further investigation.

FIGURE 21. (A) A scan without contrast-medium enhancement show swelling of a poorly defined right psoas muscle. (B) Section through the pelvis revealing swelling of the iliacus muscle with a moderately well defined lucency [asterisk] compatible with an abscess. Blood cul- tures revealed staphylococcus aureus.


Vertebral and Paraspinal Disease

Tumors and inflammatory disease arising from the vertebral bodies or paraspinal musculature may project into the retroperitoneal space. The axial plane of CT is ideally suited to demonstrate the origin, nature, and scope of the disease. Psoas abscesses will show as muscle swelling with ill-defined margins (Figure Zl), and will later have lucent centers with circumferential areas of contrast-medium enhancement [16]; in long-standing cases, calcification will be present. Malignant primary bone tumors arising from the spine are rare in children, but at Childrens Hospital of Los Angeles we have experience with a sacral Ewing’s sarcoma invading the retroperitoneal space.

Undescended Testis

Computed tomography has been employed in the localization of the testis in children with cryptor- chism [17]. In view of the irradiation involved in CT with scans at l-cm intervals from the kidneys to the groin, ultrasound is the first investigation, followed by a retrograde gonadal venogram (single film technique). Only if these two investigations are noncontributory would CT be performed.

INTERVENTIONAL COMPUTED TOMOGRAPHY WITH RETROPERITONEAL DISEASE

Over the past Z-3 years, there has been an explo- sion of interventional procedures performed on retroperitoneal structures. The procedures may be divided into (a] biopsies, and (b) drainage procedures. The latter may be for abscesses, hematomas, or urine from an obstructed renal pelvis (percutaneous nephrostomy). Many of the masses and fluid collec- tions are visible ultrasonically, and the initial needling can be guided by portable ultrasound in the special procedures radiographic suite. In those sit- uations in which the area cannot be localized by ultrasound, CT is employed. With tissue biopsies, the examination is performed completely in the CT area. With drainage procedures, the patient is trans- ferred to a fluoroscopy suite for a catheter-guide wire interchange after the initial needling unless a trocar is used that does not require fluoroscopy.

REFERENCES 1. Berger PE. Chapter title. In computerized tomography in gas-

trointestinal imaging in pediatrics. Franken EA (ed): Phila- delphia; Harper and Row; 1982.

2. Kuhn JP, Berger PE. Computed tomographic imaging of abdominal abnormalities in infancy and childhood. Pediatr Ann 1980;9:200-9.

3. Hansen GC, Hoffman RB, Sample WF, Becker R. Computed tomography diagnosis of renal angiomyolipoma. Radiology 1978;128:789-791,

4. Kuhn JP. Berger PE. Computed tomography in the evaluation of blunt abdominal trauma in children. Radio1 Clin North Am 1981;19:503-26.

5. Kuhn JP, Berger PE. Computed tomogtaphy of the kidney in infancy and childhood. Radio1 Clin North Am 1981; 19:445-61.

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Resjo IM, Harwood Nash DC, Fitz CR, et al. C.T. metrizamide myelography for intraspinal and paraspinal neoplasms in infants and children. Am J Roentgen01 1979;132:367-72.

Kuhns LR. CT. of the retroperitoneum in children. Radio1 Clin North Am 1981;19:495-501.

Brasch RC, Korobkin M, Gooding CA. Computed body tomography in children: evaluation of 45 patients. Am J Roent- genol 1978;131:2i-5. Doppman JL. Computed tomography of the endocrine glands. Categorical course on computed tomography. The American Roentgen Ray Society Meeting, May 1982. Laursen K, Damgaard-Pederson K. CT. for pheochromocytoma diagnosis. Am J Roentgen01 1980;134:277-80. Dunnick NR, Doppman JL, Geelhoed GW. Intravenous extension of endocrine tumors. Am J Roentgen01 1980;135: 471-6.

Cunningham DG, Churchill RJ, Reynes CJ. Computed tomography in the evaluation of liver disease in cystic fibrosis patients. J Comput Assist Tomogr 1980;4:151-4.

I”. Long JA, Doppman JL, Nienhuis AW, et al.: Computed tomographic analysis of P-thalassemic syndromes with hemo- chromatosis. J Comput Assist Tomogr 1980;4:159-65.

14. Boldt DW, Reilly BJ: Computed tomolgraphy of abdominal mass lesions in children. Radiology 1977;124:371-8.

15. Siegel MJ, Balfe DM, McClennan BL, Levitt RG: Clinical util- ity of CT. in pediatric retroperitoneal disease. Am J Roent- genol i982;i3a:loli-7.

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CONTINUING MEDICAL EDUCATION QUESTIONS

True or false:

1. Computed tomography is the methlod of choice for the evaluation of renal transplant complications.

2. Computed tomography is the best method to investi- gate retroperitoneal neuroblastoma.

3. Unopacified loops of bowel may simulate lymphadenopathy.

computed tomographic evaluation of the retroperitoneum in infants and children

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