Differential Diagnosis and Strategy

Solitary Focus

Common diagnoses. Focal adenosis, adenoma/fibroadenoma, papilloma.

Rare diagnoses. Lobulus, ductal carcinoma in situ (DCIS), invasive carcinoma, intramammary lymph node, phyllodes tumor.

Strategy. See Table 18.1.

A solitary focus on breast MRI should preferably be followed up after 6 months. The risk of this lesion being malignant is somewhat higher than that of multiple foci. Should this focus be a malignant lesion, the expected lesion size after 6 months is maximally 5–6 mm. The initial performance of an MRI-guided vacuum-assisted biopsy (VAB) can and should be avoided.

TABLE 18.1 Diagnostic work-up strategy for solitary focus

Strategy: No correlative finding on mammography or breast ultrasound
Mx/US BI-RADS1	MRI follow-up^a (Figs. 18.1, 18.2, 18.3).
Strategy: Correlative finding on mammography and/or breast ultrasound^b
Mx/US BI-RADS2	Mx or US follow-up^a
Mx/US BI-RADS3	Mx or US follow-up^a
Mx/US BI-RADS 4	Percutaneous biopsy (US-CB or Mx-VAB)
Mx/US BI-RADS 5	Percutaneous biopsy (US-CB or Mx-VAB)

^a Follow-up interval usually 6 months.

^b Small lesions often not found on second-look US.

Mx: x-ray mammography.

US: ultrasonography.

US-CB: US-guided core biopsy.

Mx-VAB: stereotactic vacuum-assisted biopsy.

Fig. 18.1a, b Solitary focus. No change at follow-up breast MRI examination 6 months after detection.

a Subtraction slice image: initial detection of solitary focus in the right breast (arrow).

b Subtraction slice image (follow-up 6 months later): no progression (arrow).

Fig. 18.2a, b Solitary focus. Size increase at follow-up breast MRI examination 6 months after detection.

a Subtraction slice image: initial detection of solitary focus in the left breast (arrow).

b Subtraction slice image (follow-up 6 months later): progression with focus size increase from 3 mm to 5 mm in diameter (arrow).

Histology: fibroadenoma (B2).

Fig. 18.3a, b Solitary focus. Size increase at follow-up breast MRI examination 6 months after detection.

a Subtraction slice image: initial detection of solitary focus in the left breast (arrow).

b Subtraction slice image (follow-up 6 months later): progression with focus size increase from 3 mm to 6 mm in diameter (arrow).

Histology: invasive ductal carcinoma (B5b).

Multiple Foci

Common diagnoses. Lobuli (physiological enhancement), adenosis, adenomas/fibroadenomas.

Rare diagnoses. Papillomas, DCIS, invasive carcinoma (one of the multiple foci), multiple carcinomas, intramammary metastases.

Strategy. See Table 18.2.

Multiple foci on breast MRI should preferably be followed up in the normal early breast cancer detection interval of 1 year. Should one of these foci be a malignant lesion, the expected lesion size after 12 months is maximally 8–10 mm. The initial performance of an MRI-guided VAB is not expedient because “one will always biopsy the wrong focus.”

TABLE 18.2 Diagnostic work-up strategy for multiple foci

Strategy: No correlative finding on mammography or breast ultrasound
Mx/US BI-RADS1	Examination at routine intervals (Figs. 18.4, 18.5, 18.6).
Strategy: Correlative finding on mammography and/or breast ultrasound
Mx/US BI-RADS2	Examination at routine intervals
Mx/US BI-RADS3	Mx or US follow-up^a
Mx/US BI-RADS 4	Percutaneous biopsy (US-CB or Mx-VAB)
Mx/US BI-RADS 5	Percutaneous biopsy (US-CB or Mx-VAB)