Testicular Carcinoma

Todd M. Blodgett, MD

Alex Ryan, MD

Carl Fuhrman, MD

Key Facts

Terminology

Germ cell tumors (GCT)
Non-germ cell tumors
Gonadal stromal tumors
Interstitial cell tumors
Sex cord tumors

Imaging Findings

CT or MR for initial staging
FDG PET/CT: Therapeutic response; restaging
For seminoma, sensitivity/specificity of FDG PET are 100% and 80%, of CT are 74% and 70%
FDG PET demonstrates PPV and NPV of 91% and 62% in differentiating tumor from non-tumor lesions in patients with non-seminomatous GCT
FDG PET is the modality of choice to determine therapeutic response/restaging in malignant germ cell tumors
Ultrasonography to localize mass and determine internal structure

Top Differential Diagnoses

Epidermoid Cyst
Lymphoma, Leukemia, Metastases
Focal Orchitis

Diagnostic Checklist

US for primary diagnosis
CT or MR for initial staging
FDG PET/CT for therapeutic response/restaging
Testicular neoplasms may not be FDG avid
- May lead to false negative PET; always correlate with CT

Graphic shows a large heterogeneous testicular mass

, compatible with testicular carcinoma.

Axial CECT shows a near water density mass in the right scrotum

, a nonspecific finding that was diagnosed as testicular carcinoma.

TERMINOLOGY

Abbreviations and Synonyms

Germ cell tumors (GCT): 95% of testicular carcinomas
Non-germ cell tumors also referred to as
- Gonadal stromal tumors
- Interstitial cell tumors
- Sex cord tumors

Definitions

Germ cell tumors (GCT): Malignancy arising from germ cell elements
- Seminomas
- Teratoma/teratocarcinoma (embryonal cell)
- Choriocarcinoma
Non-germ cell tumors: Neoplasm arising from non-germ cell elements
- Leydig cell tumors (LCT): From interstitial cells
- Sertoli cell tumors (SCT): From sustentacular cells lining seminiferous tubules
- Granulosa cell tumors: Rare, benign tumors
- Gonadoblastomas: Contain both stromal and germ cell elements

IMAGING FINDINGS

General Features

Best diagnostic clue: Palpable, intratesticular, homogeneous or mixed consistency hypoechoic mass on US
Location
- Germ cell tumors
  - Local: Testis, epididymis, spermatic cord
  - Regional: Retroperitoneal lymph nodes
  - Distant: Supradiaphragmatic nodes or visceral sites
  - Most common site of recurrence is retroperitoneum
- Non-germ cell tumors: 90% local (benign), 10% metastasize
- Rarely bilateral
Size: > 5 cm indicates high stage disease
Morphology
- Germ cell tumors: Solid mass with internal heterogeneity
- Non-germ cell tumors: Round, lobulated, well-circumscribed mass
  - Teratoma and choriocarcinoma often demonstrate calcification, necrosis, hemorrhage, and cystic elements

Imaging Recommendations

Best imaging tool
- Ultrasonography to localize mass and determine internal structure
- CT or MR for initial staging
  - For stage I, GCT CXR may be used at diagnosis and for follow-up
- FDG PET/CT: Restaging and response to therapy
Protocol advice
- High frequency linear array US including both testes

CT Findings

CT indicated for staging of metastasis in retroperitoneum, lymph nodes, and mediastinum/lungs
- Insensitive for undiagnosed testicular lesions
- Especially useful when metastatic disease in thorax is suspected
Lymphoma and metastatic testicular cancer may have similar appearance
- Obtain tissue sample from abnormal testicle
Lymph nodes
- Typical locations for malignant involvement include left renal hilus and retrocaval area
- Low attenuation, poorly enhancing nodes in these regions suspicious even when small
Residual low attenuation masses after treatment
- Lesions > 3 cm 4 weeks after chemotherapy have 30% chance of harboring viable tumor
- Surgical resection recommended > 3 cm
Recurrence most common in retroperitoneum; CT may identify “growing teratoma” syndrome

Nuclear Medicine Findings

Initial diagnosis
- Limited data on FDG PET evaluation of malignant non-germ cell tumors is available
- Sensitivity/specificity for seminoma
  - FDG PET: 100% and 80%
  - CT: 74% and 70%
- SUV > 3 used as cutoff for suspicion of malignancy in primary testicular tumor
Staging
- For initial staging of testicular germ cell tumors, FDG PET offers no statistical advantage over CT
- FDG PET demonstrates positive predictive value (PPV) and negative predictive value (NPV) of 91% and 62% in differentiating tumor from non-tumor lesions in patients with non-seminomatous GCT
  - Negative FDG PET studies may not exclude presence of disease (due largely to presence of teratoma)
  - Residual masses with negative FDG PET usually still require surgical resection
  - Additional FDG PET exams are without benefit in cases of elevated tumor markers and tumor progression diagnosed by CT
- FDG PET useful for identifying stage IIA in clinical stage I non-seminomatous GCT patients
Restaging
- Anterior mediastinum: Normal thymic uptake may be mistaken for disease recurrence
- Tumor marker elevation in the absence of CT changes should prompt PET scan for possibility of salvage surgery
- Overall, FDG PET is the best predictor of viable seminoma in residual masses after chemotherapy
  - Also useful in non-seminomatous GCT patients
  - Masses with residual malignancy may appear negative on PET 10-14 days after chemotherapy (“stunned” tumor)
- Post-therapy non-seminomatous GCT
  - Difficult to differentiate mature teratoma from necrosis or scar
  - Both entities have low FDG uptake
  - Non-standard dynamic imaging: Kinetic parameter for FDG transport in mature teratoma higher than those for necrosis/scar
- Longitudinal follow-up required for late relapse patients, even with negative FDG PET scan
- In complicated multiple-relapse seminoma patients, use of FDG PET has been shown to change decision on therapy in 57% of cases
Response to therapy
- FDG PET is the modality of choice for determining therapeutic response/restaging in malignant germ cell tumors
  - Best predictor of viable residual seminoma in post-chemotherapy masses
- Negative FDG PET excludes presence of viable tumor for lesions > 3 cm
  - Sensitivity 80%, specificity 100%, PPV 100%, NPV 96%
  - Compares to 74%, 70%, 34%, 92% for CT
  - Lesions < 3 cm: Sensitivity/specificity 25% and 100%
- FDG PET predicts response to therapy of germ cell tumors
  - Mean SUV of nonresponders: 2.7
  - Mean SUV of responders: 1.8
  - PPV/NPV of FDG PET in patients with raised tumor markers and negative CT: 92% and 50%
  - PPV/NPV for patients with residual mass: 96% and 90%