Castleman disease (CD) is generally regarded as a benign condition, it is more frequent in women with a median age at diagnosis in the third or fourth decade. Clinically, CD is classified as unicentric CD (UCD) and multicentric CD (MCD) based on anatomical distribution. Unicentric CD tends to be asymptomatic or present with mild symptoms. Multicentric CD can be severely or life-threatening.Recently, a novel clinical classification was mentioned,patients who have more limited lymph node involvement and are referred to as having “regional” or “oligocentric” CD [1].
According to histopathological characteristics, CD can be classified as a hyaline vascular, plasma cell, or mixed type, and the incidence rate is 72%, 18%,and 10%, respectively [2]. UCD affects multiple lymph nodes throughout the body, over 70% of patients with UCD present with the disease in the thorax, with the majority of the cases seen in the mediastinum [3]. Here, we reported an unusual case of UCD located in the lower extremity, an extremely rare site of the disease.
To the best of our knowledge, only a few cases of lower extremity CD have been reported in English literature [2, 4, 5]. Pathological findings for previously reported cases have included hyaline vascular CD and mixed cellularity CD. In the present case, pathologically demonstrated plasmacytic cell type CD, a finding which is rarely reported in the popliteal fossa.
Since the clinical signs and symptoms of UCD are often nonspecific, making them easy to miss or misdiagnose. Lesions in the popliteal fossa require careful evaluation because a number of non-neoplastic and neoplastic lesions can mimic this entity, diagnosing CD without pathological findings is difficult.Generally, the unenhanced CT/MRI scan of CD shows a nonspecific lobulated soft tissue mass, a well-defined border and clearly delineated from adjacent structures, associated with an intact envelope of the lesion.The characteristic image shows that CD is homogeneous enhancement of the lesion, usually without necrolysis liquefaction or hemorrhage, and the hypervascularity soft tissue tumor are associated with the proliferation of small and medium-sized blood vessels in the tissue of the lesion [5]. Although the relatively rare plasmacytic cell type UCD should demonstrate less intense enhancement, however, given the intense lymph node enhancement seen in plasmacytic cell type UCD, it is intuitive that plasmacytic cell type UCD would also avidly enhance [3]. Radiological differential diagnosis of solitary hypervascularity soft tissue tumor includes vascular tumors, extrapleural solitary fibrous tumors, lymphoma, soft tissue sarcoma and metastatic tumor [2].
The guidelines suggest that UCD should be managed in the first-line setting with surgery in both children and adults. Complete surgical excision will usually eliminate any systemic symptomatology and laboratory abnormalities,if present [6]. In cases of unresectable disease, aggressive local therapy with radiation should be considered for patients with symptoms or as consolidation after systemic therapy. Asymptomatic patients may be suitable for observation [7]. Oligocentric CD should be managed more like UCD [1].
This report also has some limitations. First,there was no systemic imaging was performed to look for multicenticity, but notably there were no physical findings suggestive of multicentricity.Second, UCD is virtually always HHV-8 − , but rare positive cases have been reported [6], unfortunately, no relevant viral testing was performed in this case.
In conclusion, we have described a rare case plasmacytic cell type of UCD located in the popliteal fossa which might help to enrich the clinical spectrum of this rare site and unique subtype of UCD. This case illustrates that CD should be considered in the differential diagnosis of every hypervascularity soft tissue tumor in any anatomic location, especially when they occur in the region of lymph node distribution.
