Kollisionstumor

Colonic

Collision Tumour as a cause of Intussusception. Red arrows signaling the leading point (tumour)

Renal

collision tumours: three additional case reports. Abdominal computed tomography scan showing a Bosniak 4 cystic lesion (white star) and a fleshy lesion (white line) of right kidney in Case 1 (A), a right mid-renal lesion with fat and tissular components in Case 2 (B) and a left kidney mass in Case 3 (C)

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A tumor-to-tumor metastasis, also known as a collision tumor, is a rare metastatic process in which a primary malignant tumor ('donor') metastasizes to another tumor ('recipient'), most commonly a benign tumor such as a meningioma.

Epidemiology

Tumor-to-tumor metastasis is considered very rare, with one recent 2012 review uncovering only 84 cases in a literature search .

Clinical presentation

Clinical presentation is highly variable depending on the primary donor tumor and the tumor to which it is metastasizing to .

Pathology

The most common recipient of these metastases are meningiomas with the most common donor tumors being breast and lung cancers, however many different donor (e.g. renal cell carcinoma, prostate cancer) and recipient tumors (e.g. renal cell carcinoma, thymoma, uterine leiomyoma) have been reported .

Meningiomas are the most common recipient tumor and although the reasons for why this is so remain unclear, it has been postulated that they have many characteristics that promote tumor growth, such as slow growth rate, hypervascularity, high collagen, and high lipid content .

Radiographic features

Similar to clinical presentation, radiographic features are highly variable and often CT and MRI alone are not sufficient to confidently make the diagnosis of tumor-to-tumor metastasis .

As meningiomas are the most common recipient tumor, they are most commonly described radiographically in the literature . In general, unusual radiographic characteristics and unexpectedly rapid growth in a meningioma may be prompts to consider this rare diagnosis .

CT

Appearance is variable, with the metastasis within a meningioma appearing as either hyperdense over the meningioma, or hypodense if it has a necrotic component .

MRI

Again highly variable, MRI reveals signal characteristics that are unusual for a meningioma . MR spectroscopy and MR perfusion may be additionally utilized to detect further characteristics atypical for meningioma .

Treatment and prognosis

Treatment involves resection, which is often necessary for diagnosis anyway, and management of the primary tumor . Prognosis is that of the metastasized primary malignancy.