Clinical History:
The patient is a 20-year-old male graduate student with a right
axillary "lymph node". (Images 8A-8C)
Cytologic Findings:
The cytologic smears are cellular and comprised of
mostly dyscohesive, bland-appearing spindle-shaped cells with round to ovoid nuclei, inconspicuous to
small nucleoli, and variable amounts of tapering cytoplasm (Images A and C). A few small clusters of
cells are also present (Image B). The overall cytologic features resemble benign fibroblasts.
Figure 8A - Cellular aspirate smear comprised of mostly discohesive, bland-appearing spindle-shaped cells. (Diff-Quik stain, low power)
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Figure 8B - Individual spindle-shaped cells have round to oval nuclei, inconspicuous nucleoli, and variable amounts of tapering cytoplasm. A few cell clusters are present. (Diff-Quik stain, high power)
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Figure 8C - Spindle-shaped cells as seen in Image 8B. These cells resemble bland fibroblasts. (Papanicolaou stain, medium power)
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Clinical Follow-up:
FNAB was initially interpreted as nodular fasciitis
with the following comment: "Close clinical follow-up is recommended and re-biopsy if mass fails to
resolve and/or shows evidence of progression." The patient was informed of the need for follow-up by a
sports medicine orthopedist and released from Student Health. Unfortunately, our orthopedic oncologist
was leaving to go out of town and was not able to consult on the patient. Approximately 2 years later,
he returned to UNC hospitals and underwent surgery for an anterior cruciate ligament repair of the left
knee. No complaints regarding the initial mass or physical examination of the right shoulder/axilla was
documented. A year later he returned to UNC with complaint of limitation of movement of the right
shoulder. An MRI scan revealed a large soft tissue mass, 8 x 10 cm, involving the right shoulder and
axilla. He was taken to the OR for open biopsy, ultimately followed by surgical resection and radiation
therapy. He is currently 1.5 years from the initial surgical resection without evidence of local
recurrence or metastasis.
Discussion: Plexiform fibrohistiocytic tumor
Plexiform fibrohistiocytic
tumor (PFHT) is a rare, low grade sarcoma usually arising in infants and children and less commonly
affecting adults. The tumor occurs in females more often than males. At the time of diagnosis, most
patients complain of a small (<3 cm), painless soft tissue mass localized to the dermis and/or
subcutaneous fat. The upper extremities, especially the hands and wrists, are involved in up to 2/3 of
cases followed by, in decreasing order of frequency, the lower extremities and trunk.1-2 PFHT
is very rare in the head and neck region.
PFHT has a very distinctive biphasic histologic appearance, being comprised of variably sized
histiocytic nodules admixed with infiltrative fibroblastic fascicles, creating a plexiform arrangement.
The histiocytic nodules are typically well demarcated from the spindle cell component and consist of
clusters of mononuclear cells and randomly distributed, osteoclast-type giant cells. The fibroblastic
component often closely resembles a cellular fibromatosis or nodular fasciitis with a uniform spindle
cell population arranged in fascicles and vague storiform patterns, accompanied by variable amounts of
collagen deposition. In any given tumor, the proportion of both components is variable, ranging from
cases dominated by the histiocytic nodules (fibrohistiocytic subtype), fibroblastic fascicles
(fibroblastic subtype), or equal proportions of both components (mixed subtype).2 Nuclear
pleomorphism and cellular atypia are minimal; mitotic activity rarely exceeds 3 mitotic figures/10 high
power fields. Variable numbers of extravasated red blood cells and lymphoid aggregates may be observed.
The cytologic features of PFHT have rarely been described.3 Smears are typically highly
cellular and comprised of mostly dyscohesive, bland-appearing spindle-shaped cells with round to ovoid
nuclei, inconspicuous to small nucleoli, and variable amounts of tapering cytoplasm. Histiocytes and
lymphocytes may be present. Variable numbers of osteoclast-type giant cells are seen. The cytologic
features are indistinguishable from other myofibroblastic lesions, especially nodular fasciitis or more
cellular forms of fibromatosis. It is highly unlikely that the diagnosis of primary PFHT tumor can be
rendered on cytologic material alone.
Immunohistochemical cytoplasmic staining for vimentin and CD68 is often observed in both the
osteoclast-type giant cells and mononuclear cells within the histiocytic clusters in PFHT. The spindle
cells within the fibroblastic fascicles commonly express smooth muscle actin and actin, reflecting
myofibroblastic differentiation. Desmin and S-100 protein are uniformly negative.4, 5
Overall, immunohistochemistry is non-specific and not helpful in establishing the diagnosis.No
reproducible cytogenetic abnormalities have been documented inPFHT.
PFHT should be regarded as a low grade sarcoma. Wide local excision with negative margins is
recommended. Local recurrence rates range from 12-40%, but regional (lymph node) and systemic metastases
occur in less than 5% of patients.1-2, 4 There are no clinical or pathologic features
predictive of prognosis.
Since the case was initially thought to represent nodular fasciitis, I should briefly mention this
differential diagnosis. Regarding nodular fasciitis, spontaneous regression following even incomplete
excision or FNAB is the rule rather than the exception.6 In my practice, once the diagnosis of
nodular fasciitis is rendered on FNAB, I generally recommend close clinical follow-up and re-biopsy if
the lesion continues to grow or fails to resolve in at least 2 months. It is very important that
follow-up involves an experienced orthopedic oncologic surgeon, as other surgeons may lack an adequate
understanding of the limitations of FNAB. At UNC, ALL orthopedic patients with benign and malignant
lesions are currently followed by our orthopedic oncologic surgeon. As a result of this case, this is
now policy within our orthopedic department.
References
- Enzinger FM, Zhang R. Plexiform fibrohistiocytic tumor presenting in children and young adults: an
analysis of 65 cases. Am J Surg Pathol 1988;12:818-826.
- Remstein ED, Arndt CAS, Nascimento AG. Plexiform fibrohistiocytic tumor: clinicopathologic analysis
of 22 cases. Am J Surg Pathol 1999;22:662-670.
- Angervall L, Kindblom LG, Lindholm K, et al. Plexiform fibrohistiocytic tumor: report of a case
involving preoperative aspiration cytology and immunohistochemical and ultrastructural analysis of
surgical specimens. Pathol Res Pract 1992;188:350-356.
- Hollowood K, Holley MP, Fletcher CDM. Plexiform fibrohistiocytic tumour: clinicopathological,
immunohistochemical and ultrastructural analysis in favour of myofibroblastic lesion.
Histopathology1991;19:503-513.
- Zelger B, Weinlich G, Steiner H, et al. Dermal and subcutaneous variants of plexiform
fibrohistiocytic tumor. Am J Surg Pathol 1997;21:235-241.
- Stanley MW, Skoog L, Tani EM, Horwitz CA. Nodular fasciitis: spontaneous resolution following
diagnosis by fine-needle aspiration. Diagn Cytopathol 1993;9:322-324.
