eMedicine Specialties > Radiology > Multisystem

Tuberous Sclerosis: Imaging

Author: Bennett Greenspan, MD, Instructor of Radiology, Mallinckrodt Institute of Radiology, Washington University School of Medicine
Coauthor(s): L Keith Jordan, MD, Consulting Staff, Radiology Associates PA; Charles M Glasier, MD, Professor, Departments of Radiology and Pediatrics, University of Arkansas for Medical Sciences; Chief, Magnetic Resonance Imaging, Vice-Chief, Pediatric Radiology, Arkansas Children's Hospital
Contributor Information and Disclosures

Updated: May 8, 2009

Radiography

Findings

Abnormal radiologic findings are important in diagnosing this disease and include CNS lesions of cortical hamartomas, white-matter abnormalities, and subependymal nodules (ie, hamartomas).

Most findings detectable on plain radiographs are musculoskeletal or thoracic. One half of the patients with tuberous sclerosis have musculoskeletal lesions. Changes include osteoporosis and cystic defects in the metacarpals, metatarsals, and/or phalanges. Erosions of the tufts of the distal phalanges, the result of ungual angiofibromas, may be observed. A periosteal reaction is observed in tubular bone; some authors characterize this reaction as having an undulating appearance. Heterogeneous sclerosis can affect the entire axial skeleton. Multiple bone islands with an apparent natural propensity for the diploic space may be observed. Macrodactyly and expansile-enhanced bone density that is restricted to a single rib are described. Plain skull films often reveal sclerosis or widening of the diploic space, which is related to the administration of phenytoin.

Chest radiographs rarely can depict evidence of interstitial fibrosis or honeycombing. Occasionally, the appearance of the chest is compatible with its appearance in lymphangioleiomyomatosis (LAM). The connection between tuberous sclerosis and LAM is unclear. Pneumothorax is an infrequent complication in interstitial fibrosis and LAM. Approximately one fourth of patients can have cardiac rhabdomyomas, which places these patients at risk for congestive heart failure.

Renal angiomyolipomas occur in 50-90% of patients but only rarely contain enough adipose tissue to be observed on plain radiographs. Findings on excretory urograms or retrograde pyelograms can vary widely, depending on the number and size of cysts or angiomyolipomas. These findings include bilateral renal enlargement or distortion of the collecting systems caused by cysts or angiomyolipomas. Hamartomatous polyps can be present in the colon. Gastric polyposis also can occur; this can be depicted on barium studies.

Specificity with respect to plain radiographic findings in patients with tuberous sclerosis is problematic because many of these lesions occur in other conditions; however, conventional radiographic findings often support the diagnosis of tuberous sclerosis.

Degree of Confidence

Occasionally, plain radiographs depict lucencies caused by fat in the angiomyolipoma; this finding can suggest the diagnosis of tuberous sclerosis. Distortion of the renal collecting system as a result of multiple cystic lesions may be indistinguishable from findings in autosomal dominant polycystic kidney disease.

False Positives/Negatives

Findings on excretory urograms and retrograde pyelograms can include bilateral renal enlargement or distortion of the collecting system; these can mimic the findings in autosomal-dominant polycystic kidney disease.

Computed Tomography

Findings

Overall, CT reveals intracranial abnormalities in 85% of patients with tuberous sclerosis. Frequently, CT can depict extracranial manifestations of tuberous sclerosis.

CT readily depicts calcified cortical tubers and calcified subependymal nodules; the frequency of their calcification increases with patient age. According to one author, more than 80% of the lesions can become calcified. Cortical tubers are often seen as low-attenuating peripheral lesions on CT scans; these are more easily identified with MRI.

Subependymal nodules are found mostly along the lateral ventricles. They may appear as localized projections into the ventricular cavity. These nodules may enhance after the intravenous administration of contrast material, although contrast enhancement is more difficult to recognize on CT scans than on other images, particularly in calcified lesions. Contrast enhancement does not imply malignant transformation.

In 10-15% of patients, subependymal nodules may transform into giant cell astrocytomas. These tumors are benign and usually occur at or near the foramen of Monro. These lesions typically appear inhomogeneous and usually have an inhomogeneous enhancement pattern after the intravenous administration of contrast material. They frequently are calcified, usually enlarge over time, and commonly cause obstructive hydrocephalus.

Angiomyolipomas often have low attenuation values if they contain sufficient fat, but they are indistinguishable from other renal tumors if they contain little or no lipid. Varying amounts of nonlipid tissue and hemorrhage can be visualized on CT scans of angiomyolipomas. Generally, calcification is not seen in angiomyolipomas.

Cystic lesions commonly occur in this disease, and they are well characterized at CT. However, cystic lesions are indistinguishable from simple cysts, including those with well-defined walls, and they have attenuation similar to that of fluid and mural calcification. Multiple cysts can distort the renal collecting system; with this finding alone, tuberous sclerosis is indistinguishable from polycystic kidney disease.

CT reveals the cystic and interstitial changes in the lungs of patients with tuberous sclerosis. Abnormal findings include interstitial thickening, alveolar destruction, and honeycomb lung; these are pathologically indistinguishable from those in lymphangioleiomyomatosis (LAM). Some authors consider LAM to be a forme fruste of tuberous sclerosis.

Degree of Confidence

The cortical tubers seen on CT may be somewhat nonspecific if they are not calcified. The lesions can be isoattenuating on CT scans and therefore escape detection.

In the neonate, periventricular calcifications are usually secondary to toxoplasmosis, other agents (syphilis, varicella-zoster, parvovirus B19), rubella, cytomegalovirus, and herpes simplex (TORCH) infection rather than tuberous sclerosis.

The appearance of cystic lesions in tuberous sclerosis can be indistinguishable from that of simple cysts or polycystic kidney disease; however, the presence of 1 or more simple cysts in tuberous sclerosis without angiomyolipomas is rare.

False Positives/Negatives

In tuberous sclerosis, renal cysts are identical to simple cysts on CT scans. The presence of multiple cysts can distort the renal collecting system, and they can be indistinguishable from those of polycystic kidney disease, including those with smooth walls. These cysts also have attenuation levels in the range of that of fluid and mural calcification.

Angiomyolipomas with minimal or no fat can mimic other lesions on CT scans including renal cell carcinoma which can occur in patients with tuberous sclerosis.

Magnetic Resonance Imaging

Findings

MRI is the imaging modality of choice for evaluating intracranial lesions of tuberous sclerosis. Cortical tubers, or hamartomas, are the most characteristic lesions of tuberous sclerosis; they are detected on MRIs in 95% of patients. The appearance of cortical tubers on MRIs varies with patient age. In neonates and young children, the cortical tubers and subependymal nodules are hyperintense on T1-weighted images and hypointense on T2-weighted images. In older children and adults, the cortical and subependymal lesions are isointense or hypointense on T1-weighted images. They are hyperintense relative to gray matter, as well as white matter, on T2-weighted images, depending on the presence of calcification.^8,9,10

Enhancement of cortical and subcortical lesions is uncommon and occurs in fewer than 5% of the cases. When enhancement is present, it does not suggest neoplasia. Enhancement of subependymal nodules is common, and it is better visualized on MRIs than on CT scans.

MRIs depict several distinct patterns of white matter lesions, including straight or curvilinear radial cerebral bands, wedge-shaped abnormalities, nonspecific conglomerate lesions, and cerebellar radial bands. White matter lesions in older children and adults typically are isointense or hypointense on T1-weighted images compared with white matter and hyperintense on T2-weighted images compared with gray matter and white matter. A small percentage of white matter lesions enhance after the administration of contrast material.

Subependymal nodules are detected in 95% of patients. Subependymal giant cell astrocytomas appear inhomogeneous, with intense enhancement after the administration of contrast material. The fat in angiomyolipomas usually can be recognized; however, MRI has no specific advantage in its depiction compared with CT.

Degree of Confidence

The inability of MRI to definitively depict calcification does not undermine its diagnostic accuracy because MRI can delineate cortical tubers, white-matter lesions, subependymal nodules, and subependymal giant cell astrocytomas.

Ultrasonography

Findings

Hamartoma of the kidney, which has the histologic features of an angiomyolipoma, is one of the primary manifestations of renal involvement. Hamartomas contain varying amounts of mature adipose tissue, smooth muscle, and blood vessels and usually develop in young adults and enlarge slowly. Usually, hamartomas are asymptomatic; however, they can cause flank pain, hematuria, or an abdominal mass, which may be palpable. Hamartomas usually are multiple and bilateral. Malignant degeneration of hamartomas into renal cell carcinoma can occur, but this change appears to be rare. On sonograms, the lesions are highly echogenic because of their high fat content. A finding of multiple angiomyolipomas with a high fat content is highly suggestive of tuberous sclerosis.

Angiomyolipomas can bleed and cause renal parenchymal hemorrhage, as well as subcapsular or retroperitoneal hemorrhage. Renal cysts are another primary manifestation of renal involvement. Cysts almost always are multiple; typically, they are bilateral. On sonograms, cysts are anechoic and may be indistinguishable from findings in autosomal dominant polycystic kidney disease. The kidneys may be enlarged.

Degree of Confidence

Multiple angiomyolipomas in patients of either sex or an angiomyolipoma in a male patient is suggestive of tuberous sclerosis and indicates the need for further workup. Sporadic angiomyolipomas can be unrelated to tuberous sclerosis. These usually are solitary and occur in middle-aged women.

Angiomyolipomas usually are intensely hyperechoic on sonograms, but they may be difficult to distinguish from renal cell carcinoma, which also can be hyperechoic. Rarely, a renal cell carcinoma may contain some fat.

False Positives/Negatives

Cystic lesions of tuberous sclerosis may mimic simple renal cysts, as well as the cysts of autosomal-dominant polycystic kidney disease.

Nuclear Imaging

Findings

Nuclear medicine studies may have a minor role in the assessment of this condition. In patients who have intractable seizures, epileptogenic foci may originate from a single tuber. Single-photon emission CT (SPECT) imaging of the brain is useful during the ictal phase of seizures to detect the hyperperfusion of a seizure focus; this information can be valuable because surgery can be an option.

Positron emission tomography (PET) imaging may also be helpful in patients with seizures. PET imaging with F-18-fluorodeoxyglucose can localize tubers, which appear hypometabolic. Experimental studies using C-11 alpha methyl tryptophan (AMT) may become useful. In early studies, tubers acting as seizure foci appear hyperintense on a C-11 AMT PET images.

Renal scintigraphy demonstrates multiple hypoperfused and hypofunctioning lesions, such as cysts or angiomyolipomas; however, these findings are nonspecific.

Angiography

Findings

Angiography is dominant in the characterization of vascular derangements associated with tuberous sclerosis. Some authors believe that progressive degenerative changes or compromise of the media results in aneurysms. Thoracic and abdominal aneurysms can develop in patients as young as 10 years. Intracranial aneurysms also can be present, and one source proposes that these should be included as a nonprimary diagnostic feature of tuberous sclerosis.

Generally, angiography is not necessary to evaluate the kidney. However, if performed, angiography may demonstrate hypervascularity, neovascularity, and small arterial aneurysms in the angiomyolipomas. Cystic lesions are avascular. Findings believed to be suggestive of angiomyolipomas include pseudoaneurysms and a lack of arteriovenous (AV) shunting. AV shunting is common in renal cell carcinoma.

Percutaneous embolization may be helpful in controlling intratumoral hemorrhage from renal angiomyolipomas, especially if multiple lesions are present; in this situation, surgery may be difficult or impossible to perform.

Degree of Confidence

Angiographic findings of hypervascularity, neovascularity, and small artery aneurysms also can be observed in renal cell carcinoma. These entities may be difficult to distinguish on angiograms. The presence of AV shunting may help distinguish the entities because AV shunting is common in renal cell carcinoma but rarely, if ever, observed in angiomyolipomas of tuberous sclerosis.

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