Direct intracranial invasion of eccrine spiradenocarcinoma of the scalp: a case report and literature review

Eccrine spiradenocarcinoma (SC), also known as malignant eccrine spiradenoma, is a rare malignant cutaneous adnexal neoplasm arising from long-standing benign spiradenoma [1]. A history of trauma to preexisting spiradenoma has been reported [1]. A connection to Brooke-Spiegler Syndrome, an autosomal-dominant genetic disorder phenotypically characterized by multiple skin tumors such as spiradenomas, cylindromas, trichoepitheliomas and tumors of the parotid gland, is also suspected [1, 2]. In 1971, Dabska provided the first description of a case of malignant transformation of eccrine spiradenoma [3]. The most common locations are the extremities, although reports have also described occurrences on the face, scalp and chest. According to a review of the literature, median patient age is 60 years (range, 8–92 years) and the sex distribution is balanced [2]. The most common symptoms are accelerated growth, pain, and ulceration, typically present for more than 2 years. Metastatic spread to lung, bone, lymph nodes, liver, kidney, and breast has been documented [2, 4]. SC with distant metastasis progresses aggressively and the prognosis is dismal [4]. SC commonly shows the key histopathological features of spiradenoma, comprising dermal basaloid islands with multiple cuticle-lined ducts sprinkled with lymphocytes, although specific diagnostic markers have yet to be identified. Morphological grading is reportedly associated with the clinical course. The only recommended treatment is wide local excision with tumor-free margins. The efficacies of adjuvant chemotherapy or radiotherapy have yet to be established.

Malignant skin tumors rarely show direct intracranial invasion. However, once the intracranial structure is infiltrated, wide local excision with sufficient margins can become unavailable, particularly when the venous sinuses are involved. Radical treatment can thus become difficult without effective adjuvant therapy. Here, we report an extremely rare case of scalp eccrine SC that showed direct intracranial invasion, repeated recurrences after surgery, and the effectiveness of adjuvant high-precision external beam radiotherapy (EBRT), which does not appear to have been reported previously.

Eccrine SC is a rare malignant cutaneous adnexal neoplasm arising from benign spiradenoma of the eccrine sweat gland [1]. Staiger reported that in SC cases, recurrence-free survival, tumor recurrence and death were seen in 37.2% (45/121), 17.4% (21/121) and 10.2% (13/121), respectively, with a median follow-up of 24 months [2]. Metastatic spread to multiple organs has been documented. The overall prognosis of eccrine SC is poor. In a meta-analysis of eccrine SCs, 24 patients harboring distant metastasis showed a median survival of 16 months with limited efficacy from adjuvant chemotherapy and/or EBRT, while 35 cases without distant metastasis treated with local resection achieved a disease-free survival rate of 100% within a mean follow-up of 33 months [4]. An aggressive surgical approach for SC is therefore supported in the absence of metastasis.

Five cases of eccrine SC of the scalp have been reported previously (Table 1) [5‐9]. All cases were primarily treated with excision and skin grafting. Three showed no recurrence or distant metastasis [7‐9]. One developed metastasis to the neck, causing compression of the sixth cervical vertebral body [6]. Another showed local recurrence and metastases to the lung, liver and pelvis, which were treated with chemotherapy in the form of epirubicin, cisplatin and capecitabine, but showing no regression [5]. Those two cases had involved relatively large primary lesions.

The present report describes the first case of scalp SC with intracranial extension, as the five cases described above showed no intracranial extension. To the best of our knowledge, only one case report has described eccrine SC with direct intracranial extension [10]. That case involved a large exophytic tumor on the face invading the middle cranial fossa. Craniotomy and debulking of the tumor were performed, then the patient was transferred to a palliative care team and died 5 weeks after diagnosis.

Our search of the literature identified 20 cases of scalp sweat gland tumors with intracranial invasion (Table 2) [10‐28]. These consisted of four benign tumors and 16 malignant tumors. Hidradenocarcinoma was the most common pathology, with 5 cases, and only one case was SC. Tumors were attached to the SSS in 7 cases, sigmoid sinus in 2 cases, confluence of sinuses in 1 case and transverse sinus in 1 case. The venous sinuses were preserved in all cases. In most cases, primary treatment was surgical resection. Eleven cases received radiotherapy (prescribed dose range, 20–60 Gy) including four cases that were administered chemotherapy, and one case that received an unspecified “adjuvant therapy”. None of tumor size, depth of extension, venous sinus involvement or adjuvant therapy were associated with recurrence in this limited number of cases. Nine cases developed local and/or distant recurrence. Even two non-malignant cases showed local recurrence, as did the present case, implying the necessity of careful follow-up.

In malignant skin tumors, wide local excision with 1-cm, tumor-free, circumferential and deep margins is recommended for primary treatment [4]. However, resection with the margins could be difficult in cases where the tumor shows intracranial invasion. In the present case, repeated tumor recurrence was seen after multiple surgical resections. Tumor-free margins were secured only in the scalp and skull. Tumor detachment from the SSS followed by electrocoagulation proved insufficient for tumor control. However, sacrifice of the venous sinuses, particularly the SSS, is expected to cause brain swelling, infarction, hemorrhage and even life-threatening conditions [29, 30]. If the venous sinus had been spared tumor involvement, dural resection with the tumor could have been performed to obtain a tumor-free margin.

Although radiotherapy is generally not recommended as the primary therapy for sweat gland carcinomas, due to their radioresistance [31], five cases of SC treated by radiotherapy have been reported [32‐36]. Rebegea reported a case of SC in the femoral region with lymphatic metastasis treated using wide local excision and lymph node dissection, followed by 50 Gy of radiotherapy to the tumor cavity and inguinal lymphatic nodes, and six courses of chemotherapy comprising carboplatin and paclitaxel, resulting in postoperative recurrence-free survival of 3 years [32]. Tay reported a case of eccrine SC in the lower leg with lymphatic metastasis treated by wide local excision and lymph node dissection, followed by radiotherapy of 59.4 Gy to the tumor bed and 45 Gy to the inguinal and pelvic lymph nodes. Local recurrence occurred 9 months after completion of this treatment [33]. In the other three cases, details of radiation dose and outcomes were not reported [34‐36].

In the case reported here, image-guided high-precision EBRT with the SIB-VMAT technique to deliver higher dose to the gross tumor was administered after the third surgery and tumor remission was attained within 3 months. No other reports have described the efficacy of photon EBRT. The SIB-VMAT prolonged the time to recurrence from 12 months (after the second surgery) to 20 months (after the third surgery). Notably, recurrence after the EBRT was limited to around the SSS, where unresectable tumor had been left, even though the tumor was seen to show broad attachment to the dura at the third operation. Immediate adjuvant EBRT after maximal resections like the first or second surgeries might have yielded longer, better tumor control [37], which was not performed in the present case. The fourth operation and second EBRT were palliative treatments and follow-up examinations were not conducted.

We have reported a rare case of scalp SC with direct intracranial invasion. Radical resection with tumor-free margins represents the mainstay of treatment, but involvement of the venous sinuses makes this method unfeasible. High-precision EBRT with sufficient tumor dose in combination with maximal resection preserving the venous sinuses could be a treatment option for longer tumor control.