Teaching Case

We present the case of a 59-year-old female patient who had a tumour in the palm of her hand after several months of evolution. The mass was painless, showing slow growth during the last month.

An ultrasound was performed, revealing a subcutaneous tumour of 3 cm maximum diameter, with a cystic appearance but heterogeneous content and a proximal solid pole measuring 1 cm (Figure 1a). The solid pole showed Doppler signal and low-flow arterial spectral waves (Figure 1b). The MRI depicted a heterogeneous lesion with a hypertense fluid component on both T1WI and T2WI (Figures 2a and 2b), and a solid component characterised by gadolinium enhancement (Figures 2c and 2d).

A biopsy of the solid portion was performed with a histological diagnosis of poroid hidradenoma (Figure 3).

Poroid hidradenoma (PH) is a variant of the eccrine poroma, which belongs to the group of poroid neoplasms described in 1990 by Abenoza and Ackerman [1]. The age of the patients ranges from 13 to 86 years, with a peak in the sixth or seventh decade of life and a discrete predilection for the female sex [2], as in our case. It usually appears clinically as a solitary nodule, commonly on the head, limbs, trunk, and neck [3].

Regarding the image characteristics of the PH on ultrasound, it has been described as a predominantly cystic lesion with a mural node [2]. In our case, there was an intense vascular network, as evidenced by Doppler US. On MRI, it has also been described as a cystic lesion with a solid pole that can show contrast enhancement. As in our case, the cystic portion may appear hyperintense on T1WI; this characteristic has been described as likely related to blood content as a result of microscopic haemorrhage [4].

There is controversy about the origin of PH, which is believed to arise from the sweat glands of either eccrine or apocrine origin. They are heterogeneous tumours that contain variable amounts of functional sweat glands, which may explain the variable characteristics in radiologic studies [4].

A malignant variant has also been described, so a histological study is necessary for histological confirmation [5]. Histologically, PH is characterised by well-delimited tumours consisting of solid portions and large cystic spaces without epidermal connection. Tumour cells consist of small monomorphic poroid cells and large cuticular cells, a defining characteristic of PH [3].

Complete surgical removal of HP is the treatment of choice, emphasising the importance of histological examination of the removed tissue to confirm the complete removal. The prognosis is excellent, given its benign nature and its low recurrence rate after proper surgical removal [3,4].

Conclusion

Poroid hidradenoma (PH) should be considered in the differential diagnosis of a surface mass in the hand. The correlation of magnetic resonance and ultrasound imaging with histopathological analysis helps to confirm the diagnosis and guide the appropriate treatment.

Written informed patient consent for publication has been obtained.