Year : 2004 | Volume
: 14 | Issue : 3 | Page : 273--278
Varied appearances of extragonadal germ cell tumors on radiographs and CT : A pictorial essay
RB Dubey, AN Hegde, YP Sachdev
A/75/747-MIG Colony, Bandra (E), Mumbai-400051, India
A N Hegde
A/75/747-MIG Colony, Bandra (E), Mumbai-400051
|How to cite this article:|
Dubey R B, Hegde A N, Sachdev Y P. Varied appearances of extragonadal germ cell tumors on radiographs and CT : A pictorial essay.Indian J Radiol Imaging 2004;14:273-278
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Dubey R B, Hegde A N, Sachdev Y P. Varied appearances of extragonadal germ cell tumors on radiographs and CT : A pictorial essay. Indian J Radiol Imaging [serial online] 2004 [cited 2020 Jan 19 ];14:273-278
Available from: http://www.ijri.org/text.asp?2004/14/3/273/28602
Extragonadal germ cell tumors (EGCTs) as the name suggests are those germ cell tumors found at sites other than the gonads. They pose a challenge to the radiologist as diagnosis of these tumors demands a sound knowledge of their embryology and their pathological characteristics.
EGCTs are derived from totipotent germ cells which develop in yolk sac. These cells then migrate along the midline to the region of developing embryonic gonads[Figure 1]. If they are trapped or deviated from path of descent they remain there and then may undergo malignant change to develop into extragonadal germ cell tumors. Hence, they may be found anywhere at or near the midline of the body, for example in the mediastinum, brain, retroperitoneum, spine and sacrococcygeal region.
Owing to their origin from totipotent germ cells they contain mixture of tissues derived from all three germ cell layers. Dermoid cyst contains mainly ectodermal tissues while solid teratoma usually contains tissues of ectodermal, mesodermal and endodermal origin 
A plain radiograph is an initial investigation in the radiological work up of these tumors. However, for an alert radiologist it may prove to be diagnostic! CT provides the exact anatomical location, relations to surrounding structures, the extent and helps in characterizing these tumors. Benign/malignant nature of these tumors are well characterized by CT. The fat/calcium/ cystic contents of some of these tumors are well depicted by CT scans.
Additional role of CT in performing CT guided biopsies/FNAC of lesions is well known.
With this background, a few cases of EGCTs from various anatomical regions have been reviewed.
Wide spectrums of the germ cell tumors occur in the brain. Of these, germinomas and teratomas are commonly encountered.
These are tumors of multipotent cells that recapitulate normal organogenesis. They contain tissues that represent a mixture of two or more germ layers. These tumors are more common in males. Teratomas are tumors of young children .
On CT scans, they appear as well defined rounded heterogeneous lesions with areas of CSF, fat, calcification and soft tissues.
On MR, these tumors appear heterogenous depending on their internal contents. Fluid appears as low signal on T1 weighted images and as high signal on T2WI. Fat would give a high signal on T1WI and calcium gives a low signal on T1WI and T2WI.
They account for 2/3rd of germ cell tumors and for about 40% of all pineal region neoplasms .
There is a strong male predominance.The peak age of presentation is in the second decade . Pineal and suprasellar regions are common sites
Precontrast CT shows slightly hyperdense mass. On administration of intravenous contrast, uniform and strong enhancement of the mass is seen.
Diffuse subarachnoid and ependymal spread is also common. Because they are uncapsulated the germinomas may also invade the thalamus and adjacent structures  [Figure 3 and 4].
These tumors show intense uniform enhancement on post contrast T1WI on MR and is useful to assess tumor spread.
Choriocarcinomas, Endodermal sinus tumors and Embryonal cell carcinomas are rare germ cell tumors with nonspecific imaging findings. Patients with these tumors may have elevated levels of Alpha-fetoprotein or Beta Human Chorionic gonadotropin or both in their sera.
Germ cell tumors are the second most common cause of anterior mediastinal mass in children and the most common cause of fat containing lesion.
The commonest germ cell tumors in the mediastinum are dermoid cyst and teratoma (which may be benign or malignant).
This group of tumors also includes choriocarcinomas, embryonal cell carcinomas, Endodermal sinus tumors and seminomas.
Benign cystic teratoma and dermoid cyst
Benign cystic teratomas are more common than the malignant forms and are seen in all age groups particularly in adolescents and young adults with females slightly out numbering males. On CT scans benign cystic teratoma and dermoid cyst have similar appearances.
On plain films, appearance is that of a round or oval soft tissue mass which usually projects to only one side of the anterior mediastinum.[Figure 5]
CT is usually sensitive for detecting calcifications in the wall and fat collections within the cyst. The density within the cyst may be that of fat, water or soft tissue .A fat fluid level and amorphous bone or teeth occasionally can be seen in these tumors.[Figure 6]
Malignant Germ Cell tumors
These tumors are commoner in males. They secrete substances like human chorionic gonadotropin and alpha-fetoprotein, which can be used as markers to diagnosis and to monitor the tumor.
A malignant germ cell tumor appears as a lobulated soft tissue mass, which projects on both sides of the anterior mediastinum [Figure 7] and [Figure 8]
On CT they typically appear as heterogeneous soft tissue density masses containing low density areas of necrosis. Rarely they contain calcification .[Figure 9]
Intradural dermoids tumors are considered one of the congenital midline cystic tumors. They account for nearly 20% of intradural tumors seen during the first year of life. The lumbar spine is the commonest site .
CT myelography will show the exact location of the mass, whether it is extradural or intradural.
On CT, dermoids have a variable imaging appearance but usually resemble fat. They are well defined round to oval lesions situated in the bony spinal canal with low-density areas containing fat and fluid. Calcified areas may also be seen within these tumors [Figure 12] and [Figure 13].
Displacement and compression of the thecal sac can be studied and reconstruction in sagittal or coronal planes is possible.[Figure 14]
MRI is extremely useful to determine the exact location of the tumor in relation to spinal cord and also to assess its effect on spinal cord and nerve roots.
They are tumors of childhood, more common in girls. These lesions may present with a predominantly internal or external component on the basis of which they are classified into four types-
Type 1: External
Type 2: Predominantly external with a small portion that extends into the pelvis
Type 3: Predominantly intrapelvic
Type 4: Completely intrapelvic with no extrapelvic component.
They may be benign or malignant.
In general, predominantly fluid filled teratomas are benign, whereas teratomas containing predominantly solid components are more likely to be malignant.
Calcium is more commonly seen in benign lesions. Malignant lesions metastasize to the chest.
CT demonstrates bony destruction when there is involvement of sacrum and coccyx. Cystic component is well demonstrated by CT and the solid component shows enhancement on contrast enhanced scans.
Retroperitoneal teratomas are usually diagnosed before the patients are 6 months old although occasionally patients will not be recognized until they become adults .
CT scan may show calcification, osseous elements and fatty components. A fat fluid level, hair balls and dermoid plugs have been noted by various authors ,,. Presence of fluid density areas fat fluid levels and calcification help to differentiate these tumors from other fat containing tumors.[Figure 16], [Figure 17] and [Figure 18]
These benign tumors may be complicated by infection, torsion or rupture. Incidence of malignancy is less than 1%. Loss of the normal fat plane around the tumor may be an early indicator of malignant change.
Dermoid cysts of the orbital wall occur most often in the first decade of life when they present with physical signs of proptosis or progressive swelling of upper eyelid or focal fullness in the medial or lateral aspect of the eye.
On CT, dermoid cysts have well defined margins, appear cystic with the attenuation values in their center ranging from that of CSF to that of fat. The wall is noted to enhance, where as the central portion remains the same in density.[Figure 19]
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