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1 Division of Diagnostic Radiology, National Cancer Center Hospital and Research
Institute, 5-1-1, Tsukiji, Chuo-Ku, 104-0045 Tokyo, Japan.
2 Division of Pathology, National Cancer Center Hospital and Research Institute,
Chuo-Ku, 104-0045 Tokyo, Japan.
3 Division of Radiation Oncology, National Cancer Center Hospital and Research
Institute, Chuo-Ku, 104-0045 Tokyo, Japan.
Received January 24, 2003;
accepted after revision March 27, 2003.
Address correspondence to U. Tateishi.
Abstract
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MATERIALS AND METHODS. Records of 445 pathologically confirmed retinoblastomas were retrospectively reviewed. Thirty-four patients with recurrent retinoblastomas and 15 patients with second primary neoplasms who underwent CT and MRI were evaluated by two radiologists with agreement by consensus.
RESULTS. Invasive patterns of recurrent tumors included type A, intraocular tumor (n = 13); type B, intraorbital tumor with spread into the optic nerve shown as enlargement and marked enhancement of the optic nerve on contrast-enhanced CT or MRI (n = 6); and type C, tumor extending to the lateral aspect of the orbit and invading the brain via the sphenoidal bone (n = 2). Thirty-eight percent of patients with recurrent tumors had distant metastases (n = 7) or leptomeningeal metastases (n = 6). Leptomeningeal metastases were found only in recurrent tumors. Second primary neoplasms included osteosarcoma (n = 5), rhabdomyosarcoma (n = 5), meningioma (n = 4), and other tumors (n = 3). A significant difference was seen between the patients' ages at the time of diagnosis of recurrent tumors and second primary neoplasms (p < 0.0001). Extraorbital tumors were found more frequently among second primary neoplasms than among recurrent tumors (p < 0.001).
CONCLUSION. Both recurrent tumors and second primary neoplasms in patients with retinoblastoma often show characteristic imaging features. The tumor distribution on CT and MRI may help in differentiating recurrent tumors and second primary neoplasms.
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The incidence of second primary neoplasms after retinoblastoma increases with the length of time from initial diagnosis, with a cumulative incidence of 8.4% 18 years after diagnosis [10]. However, a short latency has been found among patients with recurrent tumors, and the incidence may be overestimated because of difficulties in distinguishing second primary neoplasms from recurrent tumors. Second primary neoplasms often show both high-grade and undifferentiated features on microscopic observation, making them difficult to diagnose and distinguish from the small, undifferentiated round cell tumors that are characteristic of recurrent retinoblastomas [14-21]. Although the CT and MRI findings of patients with retinoblastoma are established, there have been only a few descriptions of second primary neoplasms in patients with retinoblastoma [22]. In our study, we retrospectively reviewed and described CT and MRI findings in recurrent tumors and second primary neoplasms in patients with retinoblastoma.
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Of the 49 patients evaluated, data regarding age at diagnosis; sex; family history; histologic subtype; location; latent period; and all initial treatment for primary tumors including enucleation, chemotherapy, radiation therapy, and treatment of recurrent tumors and second primary neoplasms were documented. Patients with recurrent tumors or second primary neoplasms received combined modality therapy consisting of surgical resection or biopsy, followed by combination chemotherapy either in standard doses or in escalating doses with autologous bone marrow or peripheral blood stem cell transplantation, with or without radiation therapy. The latent period was calculated from the time of initial diagnosis to the time of diagnosis of recurrent tumors or second primary neoplasms. All tumors in the field of radiation were so classified if they appeared to be originating in the eyelids, orbits, paranasal sinuses, temporal bones, or soft tissues overlying the temporal bone region.
CT and MRI examinations were reviewed by two radiologists with agreement by consensus. The images of 49 patients included both CT and MRI (n = 27), only CT (n = 3), or only MRI (n = 19). Unenhanced CT scans were obtained in 30 patients, and contrast-enhanced CT scans were obtained in 24 patients with the use of IV iodinated contrast material. Section thickness ranged between 5 and 10 mm. CT scans were evaluated for predominant attenuation; homogeneity or heterogeneity; and the presence of calcification, bone destruction, surrounding edema, and tumor enhancement.
MRI was performed using 1.5-T systems. Using the spin-echo technique, we obtained T1-weighted images (TR range/TE range, 400-660/12-15) in the axial and coronal planes. T2-weighted spin-echo or fast spin-echo images (3000-5700/80-118) were then obtained in the axial and coronal planes. Whole-brain images were obtained with a field of view of 30-40 cm, an image matrix of 128 x 256, and a slice thickness of 5-10 mm. Locations were judged by the type of margin, extent of tissue involvement, internal architecture, presence of invasion to surrounding tissue, size, and signal characteristics on T1- and T2- weighted images. Tumor size was determined by the largest diameter in the axial plane of CT scans or MRIs. Locations were correlated with the radiation field in all patients. Signal characteristics were described as hypointense, isointense, or hyperintense relative to the surrounding structures: muscle or white matter. MRIs obtained after the IV administration of a gadolinium chelate with T1-weighting (n = 30) were evaluated for the degree and type of enhancement.
For evaluation of recurrent tumors in patients with retinoblastoma, we categorized growth patterns into three types for assessing recurrent retinoblastoma: intraocular tumor (type A), intraorbital tumor with local spread into the optic nerve (type B), and tumor extending to the lateral aspect of the orbit and invading the brain via the sphenoidal bone (type C).
CT and MRI findings were assessed in both recurrent tumors and each histologic type of second primary neoplasms. We also assessed CT and MRI findings to assist in the differentiation of recurrent tumors and second primary neoplasms.
The data obtained related to disease status regarding retinoblastoma and the second primary neoplasms in all patients. Current status was documented by follow-up examination, and follow-up was calculated in months from the date of initial diagnosis to the most recent follow-up. Differences between subgroups were analyzed for correlations with the chi-square test, Fisher's exact probability test, or Spearman's rank correlation coefficient test. The interobserver variation of the extent of various abnormalities was evaluated with the Spearman's rank correlation coefficient test. A p value of less than 0.05 was considered a statistically significant difference.
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Imaging Features in Recurrent Tumors
Sixty-two percent of patients with recurrent tumors had local lesions.
Invasive patterns (Fig. 1) of
recurrent tumors identified on CT or MRI included type A, intraocular tumor
(n = 13, 38%) (Fig.
2); type B, intraorbital tumor with spread into the optic nerve
shown as enlargement and marked enhancement of the optic nerve on
contrast-enhanced CT or MRI (n = 6, 18%)
(Fig. 3); and type C, tumor
extending to the lateral aspect of the orbit and invading the brain via the
sphenoidal bone (n = 2, 6%) (Fig.
4). Peripherally located intralesional calcification was found in
type A (n = 13, 100%) and type B (n = 2, 33%) tumors on
unenhanced CT. In addition, no calcification was found in type C tumors.
Tumors appeared hypo- to isointense in relation to normal temporal muscle on
T1-weighted images and of moderately high signal intensity on T2-weighted
images in all patients who underwent MRI. All localized lesions were depicted
as heterogeneously enhanced masses with a slightly irregular surface on
contrast-enhanced CT or MRI.
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Thirty-eight percent of patients with recurrent tumors had distant metastases (n = 7) or leptomeningeal metastases (n = 6) (Fig. 5). Multiple brain metastases were found in three patients. Although the signal characteristics on T1- and T2-weighted images were nonspecific, lesions showed heterogeneous enhancement on contrast-enhanced CT or MRI. One patient developed skull metastasis that was seen as focal bone destruction on unenhanced CT and a moderately enhanced mass on contrast-enhanced MRI.
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Imaging Features in Second Primary Neoplasms
Seventeen second primary neoplasms included various histologic types of
tumors. Malignant tumors consisted of osteosarcoma (n = 5),
rhabdomyosarcoma (n = 5), malignant fibrous histiocytoma (n
= 1), and meibomian gland carcinoma (n = 1), whereas benign tumors
were meningioma (n = 4) (Table
2).
Osteosarcoma was one of the frequent histologic subtypes (29%). Tumors originated from previously irradiated regions, including the intraorbit (n = 2), temporal bone (n = 1), and ethmoid bone (n = 1). One patient developed a tumor in the distal femur outside the irradiated field. Unenhanced CT scans revealed irregular masses in the orbit, temporal bone, or ethmoid bone with calcification (n = 4, 80%) (Fig. 6). Two tumors showed severe bone destruction on unenhanced CT. Contrast-enhanced CT and MRI showed heterogenous enhancement with perifocal edema (n = 5, 100%). Fluid-fluid levels, suggestive of hemorrhage, were identified in two tumors on T2-weighted images. Calcification identified on unenhanced CT corresponded in part to areas of signal voids or low signal intensity on both T1- and T2-weighted images.
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All rhabdomyosarcomas arose in the region previously irradiated, including five tumors that developed in the temporal muscle within the irradiated field and one that involved the contralateral temporal muscle, which may have received a radiation dose of 50-60% of that in the irradiated field. Unenhanced CT revealed well-defined masses with ovoid contours situated in the temporal muscle (n = 5, 100%). Five patients underwent both contrast-enhanced CT and MRI; of these, three tumors (60%) showed heterogeneous and slight enhancement relative to the adjacent muscle (Fig. 7). Fluid-fluid levels were found in one tumor on both T1- and T2-weighted images. Signal characteristics on T1- and T2-weighted images were nonspecific in the other four tumors.
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A 16-year-old girl with hereditary retinoblastoma developed malignant fibrous histiocytoma in the orbit, with severe destruction of bone identified on unenhanced CT (Fig. 8). The tumor showed nonspecific signal characteristics on T1- and T2-weighted images, but marked enhancement was found on contrast-enhanced CT scans and MRIs. A 20-year-old woman developed a well-defined mass in the eyelid that was seen on unenhanced CT and diagnosed as a meibomian gland carcinoma after a latent period of 121 months. The tumor showed nonspecific signal characteristics on both T1- and T2-weighted images, but areas of marked enhancement were found on contrast-enhanced MRIs (Figs. 9A, and 9B).
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All meningiomas originated from the previously irradiated skull base. Tumors showed hyperattenuation on unenhanced CT (n = 4), and marked enhancement was found in all cases on contrast-enhanced CT and MRI (Fig. 10). Punctate calcification was found in one case; this tumor was associated with secondary hyperplastic change of the adjacent bone. Signal characteristics were nonspecific on T1- and T2-weighted images. However, perifocal edema was found in three cases in the adjacent white matter on T2-weighted images.
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Differentiation Between Recurrent Tumors and Second Primary
Neoplasms
Peripherally located intralesional calcification was found in all type A
and in 33% of type B tumors on unenhanced CT. However, this finding was
similar to that of osteosarcoma arising in the orbit. Three invasive patterns
of recurrent tumors were identified on CT or MRI, whereas only two patients
with second primary tumors showed these patterns. However, this configuration
of invasive patterns did not assist in the differentiation of recurrent tumors
and second primary neoplasms (Table
3). Brain metastases and leptomeningeal metastases were found only
in recurrent tumors. A statistically significant difference was found in
intra- and extraorbital location of tumors between recurrent tumors and second
primary neoplasms (Table
4).
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CT and MRI can show tumor extension by three types of growth patterns in primary retinoblastoma: the endophytic type, in which the tumor projects anteriorly and grows into the vitreous; the exophytic type, in which the tumor arises intraretinally and subsequently grows into the subretinal space; and the diffuse infiltrating type, in which tumor growth in the retina appears as a plaquelike mass [14-16]. Our results also suggested that three growth patterns might exist in recurrent retinoblastoma, and that CT and MRI can detect tumor extension: intraocular tumor (type A), intraorbital tumor with local spread into the optic nerve (type B), and tumor extending to the lateral aspect of the orbit and invading the brain via the sphenoidal bone (type C).
Different types of second primary neoplasms have also been documented in previous studies, with most of the second primary neoplasms being soft-tissue sarcomas, followed by melanomas, brain tumors, leukemias, and other epithelial tumors [1-9]. In our study, the most common types of second primary neoplasms in patients with retinoblastoma were osteosarcoma and rhabdomyosarcoma.
Osteosarcoma is one of the most frequent second primary neoplasms originating from a previously irradiated region. Calcification within the tumor that depends on the amount of mineralization is observed on CT. Four of our patients showed central calcification within the mass on unenhanced CT. An important feature to diagnose osteosarcoma on CT may be central calcification within the mass situated in the irradiated field, including the intraorbit, temporal bone, and ethmoid bone. Extraskeletal osteosarcoma presents nonspecific signal characteristics on MRI: a mass with mixed low signal intensity on T1-weighted images and mixed but predominantly high signal intensity on T2-weighted images [23-25]. Fluid-fluid levels, suggestive of hemorrhage, were identified in two of our patients on T2-weighted images; this finding was consistent with a previous report [23].
Rhabdomyosarcoma also presents with rather nonspecific CT and MRI findings, but some characteristic findings were discovered in our patients. All rhabdomyosarcomas arose within the region previously irradiated. As a rule, rhabdomyosarcomas in the head and neck region grow rapidly, often in an infiltrative and destructive manner [26, 27]. However, all of our patients presented with well-defined masses with ovoid contours situated in the temporal muscle on both CT and MRI. The MRI signal characteristics and enhancement patterns identified on both contrast-enhanced CT and MRI were nonspecific. Few characteristic imaging findings reflect the degree of cellularity; the relative amounts of collagen; and the presence and extent of secondary changes such as hemorrhage, necrosis, and ulceration.
The initial therapy for primary tumors has been enucleation of the most severely affected eye and irradiation of the contralateral eye to preserve vision. Patients with hereditary retinoblastoma may have an increased susceptibility to the induction of second primary neoplasms by radiation [28].
Radiation increases the total risk in addition to the already high
incidence because more second primary tumors develop in the irradiated field
than outside the irradiated field
[2]. Sarcomas can be
categorized as radiation-induced if they meet the following criteria: tumor
must develop within the boundaries of a previously irradiated area, a
relatively long asymptomatic latent period (
4 years) must have elapsed,
the tumor must have a different histology from the original lesion, and the
tumor must be histologically confirmed
[28]. Most of our cases of
second primary neoplasms arose in the irradiated field. However, some tumors
occurred with relatively short latency and outside the irradiation field.
Similar findings have suggested that nearly all second primary neoplasms occur
among hereditary retinoblastoma tumors, and that many second primary tumors
occur outside the irradiation field, with some among nonirradiated tumors
[2,
28]. Second primary neoplasms
in patients with retinoblastoma may occur both as a result of, and
independently of, radiation therapy. However, the follow-up period and the
number of patients with second primary neoplasms in our study are not
sufficient for conclusive analysis. Further follow-up study is necessary to
evaluate the relationship between irradiation and the occurrence of second
primary neoplasms in patients with retinoblastoma.
In conclusion, several kinds of imaging features were present both in recurrent tumors and in second primary neoplasms in patients with retinoblastoma. The tumor distribution on CT and MRI may help in differentiating recurrent tumors and second primary neoplasms.
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