Solitary plasmacytoma of the skull base: A case report and literature review

Abstract

Plasmacytoma of the skull base is a rare entity. We present a case of sphenoid plasmacytoma in a 51‐year‐old woman who had nasal obstruction, intermittent epistaxis, headaches, decreasing visual acuity, and diplopia. Computed Tomography (CT) scan and magnetic resonance imaging (MRI) showed a large heterogeneous, expansile lesion measuring 75 mm × 54 mm, centered on the sphenoidal bone and the clivus. Biopsy confirmed the diagnosis of solitary plasmacytoma after ruling out systemic spread by the initial assessment. The patient was successfully managed by external beam radiotherapy and a complete response was obtained after 12 months of follow-up.

Introduction

The prevalence of plasma cell neoplasms, which make up to 2% of all human malignancies, is about 3.5/100,000 each year [1,2]. Without evidence of a systemic plasma cell proliferation, the solitary plasmacytoma (SP) is defined by a localized concentration of neoplastic monoclonal plasma cells. It's an uncommon tumor that accounts for less than 10% of all plasma cell neoplasms [3].

SP is defined by a histologically confirmed single lesion, a negative skeletal examination, and no evidence of tumor in the bone marrow [4] (Table 1). Its prognosis is conditioned by the tendency to convert to multiple myeloma (MM). MM, a malignant diffuse plasmacytosis, is thought to represent an endpoint in disease progression for patients with an isolated SP.

Table 1.

Diagnostic criteria for SP, as recommended by the international Myeloma Working Group [4]. The diagnosis of SP is based on the exclusion of systemic plasma cell disorders.

Plasma cell disorder	Diagnostic criteria
Solitary bone plasmocytoma, or solitary extramedullary plasmocytoma	1. Biopsy-proven solitary destructive lesion of bone or soft tissue mass of clonal plasma cells. 2. Absence of clonal plasma cells in bone marrow biopsy and aspirate. 3. Normal skeletal survey and magnetic resonance imaging (or computed tomography) of spine and pelvis (except for the primary solitary lesion) 4. If available positron emission tomography/computed tomography showing solitary lesion. 5. Absence of end-organ damage such as hypercalcemia, renal insufficiency, anemia, or bone lesions (CRAB) attributed to a plasma cell proliferative disorder
Solitary plasmocytoma with minimal marrow involvement	As above but: 6. Clonal bone marrow plasma cells detected but quantified to be <10%

SPs are classified into 2 distinct forms, solitary plasmacytoma of the bone (SBP) and extramedullary plasmacytoma (EMP) regarding to location. Most commonly, SP affects the axial skeleton's vertebrae and skull [3]. The EMP is most commonly seen in the head and neck, particularly in the nasal cavity and nasopharynx [3,5,6].

SP of the skull base is an extremely rare tumor, with only a few cases documented to date in the literature [3,7]. Its treatment of choice is radiotherapy as malignant plasma cells show high radiosensitivity levels [8].

We present here a case of SP of the skull base managed by radiotherapy.

Clinical presentation

A 51-year-old female presented with a 1-year history of nasal obstruction, intermittent epistaxis, headaches, decreasing visual acuity, diplopia. There was no nausea, vomiting, or seizure during the evolution of the symptoms. On physical examination showed left eye strabismus secondary to palsy of the sixth cranial nerve. There was no sensory or motor deficit in his upper and lower limbs. The rest of the clinical examination was unremarkable.

We subsequently proceeded with computed tomography (CT) scan and magnetic resonance imaging (MRI); which reported a large heterogeneous, expansile lesion measuring 75 mm × 54 mm, centered on the sphenoidal bone and the clivus, pressing against the optic nerve and the internal carotid artery, involving the nasal cavity and the nasopharynx, with the erosion of adjacent bones (Figs. 1 and 2).

Fig. 1.

Axial and Sagittal CT images showing a large heterogeneous lesion (arrows) centered on the sphenoidal bone and the clivus involving the nasal cavity and the nasopharynx, with the erosion of adjacent bones.

Fig. 2.

Cerebral MRI axial, sagittal and coronal T1-T2 weighted demonstrating a lobulated contour of sphenoidal process with heterogeneous tissue signal (arrows).

An endonasal endoscopic and multiple biopsy specimens of the mass was done. Histopathological examination revealed monoclonal infiltration of plasma cells. The nuclei are provided with a rounded shape with fine chromatin, and the cytoplasm was eosinophil in most cells (Fig. 3). Immunohistochemistry analysis showed CD-138 and anti-Lambda light chain antibodies positive staining, whereas the cells were negative for Cytokeratin, CD5, CD20, CD68 and PAX5 antibodies (Fig. 4). These morphological and immunohistochemical features confirmed the diagnosis of plasmacytoma.

Fig. 3.

Histology section (view of hematoxylin and eosin) showing diffuse sheets predominantly mature plasma cells.

Fig. 4.

Immunohistochemical staining showing strong positivity to lambda restriction CD138.

A comprehensive workup to rule out MM was made: skeletal examination, bone marrow biopsy, serum protein immunoelectrophoresis (SPEP), serum quantitative immunoglobulins levels, calcium, albumin, renal function test, and beta-2 microglobulin. The results were within normal ranges. Bence Jones protein in the 24-hour urine sample was negative.

Therefore, the diagnosis of SP of the sphenoid bone was confirmed. The patient was then referred to the radiation oncology department. She received external beam radiotherapy to a total dose of 40 Grays (Gy) in 20 fractions (2 Gy per fraction, daily, 5 fractions per week) to the planning target volume, by 3-dimensional conformal RT techniques, using multiple fields to maintain irradiation doses of surrounding normal tissues below their respective tolerance threshold (Fig. 5). RT took 28 days and was globally well tolerated. With excellent local control after 12 months.

Fig. 5.

Dosimetric planification of RT in axial (left) and sagittal (right) views, with the therapeutic isodose area (in green) covering the planning target volume (in red).

Discussion

SPolitary plasmacytoma is a rare plasma cell tumor that develops monoclonal immunoglobulin and is characterized by the proliferation of monoclonal plasma cells. The 2 forms of the disease, solitary bone plasmacytoma (SBP) and extramedullary plasmacytoma (EMP), are distinguishable by sites of origin. SBP primarily affects the axial skeleton, especially the vertebrae. Plasmacytoma is a rare tumor that originates from the skull base [3].

SPs of the skull base can be divided into anterior lesions (nasopharyngeal) and central lesions (sphenoid, clivus, petrous apex). The skull base site that is most frequently affected—representing 18% of all head and neck cases—is the nasopharynx. Less frequently seen are sphenoidal, clivus, and petrosal apical presentations [9]. Only 13 cases of SP of the Sphenoid bone have been reported in the English literature, our case is the 14th one (Table. 2).

Table 2.

Summary of 13 patients with sphenoid and clival SP, reported in the literature.

Author	Sex	Age	Site	Symptoms	Treatment	Evolution (Months)
Ampil et al. [10]	M	63	Sphenoid sinus	Headaches, diplopia	Transsphenoidal cytoreductive + CT adjuvant + XRT 54Gy	LC (3)
Siyag et al. [11]	M	41	Sphenoid+Clivus	Headaches, diplopia, strabismus	XRT 50 Gy	LC (3)
Sharifi et al. [12]	F	62	Sphenoid	Ptosis, headaches	Transsphenoidal cytoreductive+XRT	LC (6)
Miller et al. [13]	M	47	Sphenoid sinus	Headaches	XRT 64 GY	LC (62)
Marais et al. [14]	M	64	Sphenoid sinus	Headaches, diplopia	XRT 44 Gy	LC (18)
Bindal et al. [15]	F	51	Sphenoid+clivus	Diplopia	craniotomy transsphenoidal + XRT 50 Gy	LC (96)
Lakhdar et al. [16]	F	62	Sphenoid	Headaches, diplopia, anosmia	XRT	LC (12)
Mandagere et al. [17]	F	53	Sphenoid	Headaches, blurry vision	XRT 50 Gy	LC (84)
Akhaddar et al. [18]	M	83	Sphenoid	Headaches, diplopia	XRT+CT	PMM (NA)
Ping Loong et al. [19]	F	43	Sphenoid	Headaches, diplopia	XRT 50Gy	NA
Wein et al. [20]	M	48	Sphenoid sinus+clivus	Headaches, epistaxis	XRT+CT	PMM (1)
Park et al. [21]	M	32	Sphenoid	Diplopia	Transsphenoidal resection+XRT 40 Gy	LC (8)
Losa et al. [22]	F	50	Sphenoid sinus	Diplopia	Transsphenoidal cytoreductive+XRT 50Gy	LC (NA)

CT, chemotherapy; F, female; LC, local control; M, male; NA, not available; PMM, progression to multiple myeloma; XRT, radiotherapy.

Pathologic evidence of a monoclonal plasma cell infiltrate in soft tissue or a lytic bone lesion, as well as a lack of systemic involvement, is required for an isolated plasmacytoma to be diagnosed. A skeletal examination, a bone marrow biopsy, as well as tests of the serum and urine, are necessary for diagnosis confirmation of SP.

In 2014, the International Myeloma Working Group consensus have updated the definition of SP with several additional diagnostic criteria [4]. These criteria are (1) solitary lesion of bone or soft tissue with evidence of clonal plasma cells (2) histologically normal marrow aspirate and trephine biopsy, (3) normal results of skeletal survey including radiology of long bones, (4) No anemia, hypercalcemia or renal dysfunction due to plasma dyscrasia (Table 1). Our patient fits all the above-mentioned criteria.

SPs of the skull base are usually clinically significant because of the involvement of cranial nerves. Typically, the symptoms that lead to a diagnosis are related to a functional disturbance brought on by the mass's expansion. The clinical presentation mainly consists of headaches, diplopia, and visual deficit. Neuropathy and other neurologic symptoms are caused by direct compression or involvement of the cranial nerves. The sixth cranial nerve (abducens nerve) palsy is the most common symptom [8,23] (Table 2).

CT and MRI both have the potential to provide useful information in the diagnosis of SP of the skull base, however, it should be noted that there are no specific neuroimaging aspects specifically related to these tumors; MRI T1-weighted images can show an hyposignal mass with clear enhancement after gadolinium injection, and hypersignal mass in T2-weighted images [24,25]. The radiological differential diagnosis includes meningiomas, chordomas, invasive pituitary adenomas, metastatic carcinomas, and nasopharyngeal carcinomas [8,23,26].

Radiotherapy is the treatment of choice for the solitary plasmacytoma of the skull-base as it is a radiosensitive and radiocurable tumor [2,27]. Besides, surgery is suggested to obtain tissue for diagnosis, small localized lesions, and residual disease [8]. The optimal dose of radiation for SP is not well established. Doses of 40 to 45 Gy are common in practice [28]. Mendenhal et al. [29] suggested a minimum dose of 40 Gy to obtain good local control. Our patient received a total dose of 40 Gy in 20 daily fractions of 2 Gy, with excellent local control after 12 months. Adjuvant chemotherapy for solitary bone plasmacytoma has not been shown to improve progression-free survival nor progression to multiple myeloma [28].

The prognosis of bone SP remains dominated by the risk of multiple myeloma. Within a median of 2 years, 50% to 60% of patients with SP develop multiple myeloma, which is the systemic failure of this entity [30]. Therefore, surveillance must be closely continued after treatment, based on clinical examination, X-ray, SPEP, and the medullogram to detect any progression to MM. The development of MM is strongly predicted by the location of the plasmacytoma of the skull base, and the progression rate is over 50%, with a 10-year survival rate of only 16% [2].

Conclusion

SP of the sphenoid is rare. In localized tumor, the symptoms are usually non‐specific. When the tumor extends locally, visual loss, diplopia, and facial pain can be present. RT remains the treatment modality of choice achieving good rates of local control. However, long term follow up is necessary to detect any conversion to MM.

Patient consent

The patient was informed of the procedures for publication of this clinical case and gave clear consent

Author contribution

All authors were involved in the completion of this work.