Applied Radiology

In their 1996 article, Kirzner and Rosiello describe the "hump and dip" sign as a benign sonographic feature recognized in the majority of fibroadenomas.1 The sign consists of "a small, focal, smooth-contour bulge immediately contiguous with a small sulcus." Their article describes the presence of this sign in 77 of 136 (56.6%) biopsy-proven fibroadenomas while being absent in 150 documented carcinomas. The authors concluded that the "hump and dip" appearance is a reliable feature of fibroadenoma that may be used to avoid biopsy. However, we describe two cases of breast carcinoma which, on ultrasound imaging, demonstrate the "hump and dip" sign.

Patient 1

A 40-year-old premenopausal woman presented with a palpable mass in her right breast. Mammography showed the mass as measuring approximately 2 cm in diameter in the outer breast, with margins largely obscured by adjacent fibroglandular tissue. Ultrasound (5 MHz to 10 MHz linear array transducer) showed the lesion to be solid and well defined, with an echogenic capsule around only a small portion of the mass. The mass was oval and elongated in the direction of tissue planes, mildly heterogeneous in echotexture, and slightly hypoechoic to fat. The mass also displayed a lobulation, or "hump", adjacent to a gentle sulcus. Mildly enhanced sound through transmission was noted (figure 1). Fine needle aspiration of the mass showed ductal carcinoma with extracellular mucinous material. The patient was treated with total mastectomy and axillary dissection. Pathologically, the lesion had a gelatinous surface and lobulated borders on gross inspection. Microscopically, the tumor was composed of abundant extracellular mucin and numerous nests of well-differentiated malignant ductal cells floating within the mucin (figure 2). The interface between the tumor and the adjacent breast stroma was smooth, with tumor nodules indenting but not invading adjacent breast tissue. Multiple separate tumor nodules were present elsewhere within the breast. The histologic diagnosis was well-differentiated invasive mucinous carcinoma. One axillary lymph node contained a micrometastasis.

Patient 2

A 44-year-old premenopausal woman discovered a mass in her left breast that was discrete and moveable on physical examination. Mammography showed a rounded mass of 2 cm in diameter in the lateral aspect of the woman's left breast. The margins of the mass were mildly lobulated and partially obscured, with portions of the visualized margins appearing defined (figure 3). Ultrasound (7 MHz linear array transducer) showed a solid, well-defined lesion which was mildly heterogeneous in echotexture and slightly hypoechoic to fat. A clear lobulation followed by a sulcus was evident. There was no thin echogenic rim visible surrounding the mass. Mildly enhanced sound through transmission was noted (figure 4). Fine needle aspiration revealed carcinoma, which was treated by segmental mastectomy and axillary dissection. On gross inspection, the mass was variegated, with well-defined margins. Microscopically, the edges of the tumor were rounded, lobulated, and protruded into the adjacent fibrous-adipose stroma. The growth pattern demonstrated lobules of uniform-appearing malignant cells (figure 5). The lesion was diagnosed as invasive ductal carcinoma with neuroendocrine differentiation. One axillary lymph node contained a micrometastasis.

Discussion

The role of breast ultrasound has evolved in recent years from distinguishing simple cysts from solid lesions to the more detailed evaluation of solid lesions. Ultrasound also is increasingly used for guidance in aspiration and biopsy procedures. This expansion of applications has been possible due to the introduction of improved technology with digital imaging and broadband high-frequency automatically-focused transducers, which has resulted in marked improvement in near-field resolution. Sonographic characterization of breast lesions has been studied in an attempt to improve the specificity of mammography.2,3 In doing so, it is hoped that the number of biopsies for benign lesions can be reduced, conserving healthcare resources and eliminating the physical and emotional impact of biopsy for carefully selected patients.

Evaluation of the margins of a breast mass, both mammographically and sonographically, is of critical importance in determining the level of suspicion for malignancy. There is significant overlap in the imaging appearance of benign and malignant lesions-cancers can be entirely well-circumscribed and benign lesions may have spiculated margins. No single sonographic feature of a mass margin has been accepted as excluding malignancy with a sufficient negative predictive value to justify imaging follow-up rather than biopsy.

Stavros et al2 describe a spectrum of findings used for the sonographic evaluation of breast masses. Based on their methodology, if a lesion has even a single malignant characteristic (spiculation, angular margins, marked hypoechogenicity, shadowing, calcification, duct extension, branch pattern, microlobulation), it is excluded from the benign classification. If there are no malignant features and one of three combinations of benign features is

present (intense and uniform hyperechogenicity, ellipsoid shape plus a thin echogenic capsule, or two to three gentle lobulations plus a thin, echogenic capsule), the lesion is categorized as benign. Lesions that lack both benign and malignant features are considered indeterminate.2 For benign sonographic findings, the authors report a negative predictive value of 99.5% in a large series.

Based on the criteria of Stavros et al, the mass found in our first patient, while having no malignant sonographic features, would have been categorized as indeterminate and would have been biopsied, due to the absence of an echogenic capsule around the entire lesion. The mass found in the second patient also would have been considered indeterminate-the lesion was round, not ellipsoid, there was no echogenic capsule, and the lobulation cannot be considered gentle. One may argue that the sulcus in many lesions with the "hump and dip" appearance would exclude them from classification in the benign category because the lobulation is not sufficiently gentle. There is obvious subjectivity in deciding how a mass should be categorized; at some undetermined point a lobulation is no longer "gentle" and a deep sulcus becomes an angular margin. The report by Stavros et al is the strongest evidence to date that, with experience and documented results, high quality equipment, careful scanning, and a mechanism to ensure patient follow-up, ultrasound can be used to place some patients with solid masses into a follow-up program rather than having them undergo biopsy. These patients need to be carefully selected, and should be fully evaluated clinically and mammographically, as well as sonographically.4 In both of our patients, the masses were newly palpated and of sufficient concern on physical examination and imaging studies; a follow-up program, rather than biopsy, was never under consideration. For other masses with the "hump and dip" appearance, the management may not be as clear.

In attempting to improve the specificity of breast imaging, there is the risk of delaying the diagnosis of malignancy. Ultrasound will likely play an increasing role in reducing the number of benign breast biopsies performed. However, additional prospective studies are needed. The acceptance of sonographic studies for the differentiation of benign from malignant lesions is likely to be based on the presence or absence of a constellation of imaging findings, rather than a single characteristic. In our description of two examples of the sonographic "hump and dip" sign in patients with carcinoma, we find this margin characteristic is not specific for fibroadenoma and should not be used as justification for imaging follow-up rather than biopsy. AR

References

1. Kirzner HL, Rosiello DC: The "hump and dip" sign: An interesting US appearance of fibroadenomas in the breast. Applied Radiology 25(2):24-26, 1996.

2. Stavros AT, Thickman D, Rapp CL, et al: Solid breast nodules: Use of sonography to distinguish between benign and malignant lesions. Radiology 196:123-134, 1995.

3. Sickles EA, Filly R, Callen P: Benign breast lesions: Ultrasound detection and diagnosis. Radiology 151:467-470, 1994.

4. Jackson VP: Management of solid breast nodules: What is the role of sonography? (editorial) Radiology 196:14-15, 1995.

Dr. Raslavicus, Dr. March, Dr. Bur and Dr. Reed are with Baystate Medical Center in Springfield, MA.